12 April 1963

NBy 37636

u. S. NAVY

W ..3'-(;, ,//~\1//

MODEL STUDIES OF THE VLF PAC ANTENNA~

ENOL (1) TO BUSHIPS SER 69.4E-349~1. e--r

HNCD

A JOINT VENTURE

Los Angeles, California

5VLF - COMMFACPAC~~o l,.4-z: (__>

Q C:)<CA

c=e---I~

HollTIes & Narver, Inc.Continental Electronic s Manufacturing COlTIpany

DECO Electronics, Inc.

/., '

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CONTENTS

Page

1. Introduction ..•.•..••.•••••..•.•• , . • . . . . . . . . . • . . . . . . . . 1-1

2. Test Procedures .2. 1 Model Range .••.•••.•....•.•.•.••••••.•..••...•.2.2 Equipment .............................•........

2.2. 1 Effective Height Measurements .•.......•...2.2.2 Static Capacitance Measurements •.•......•2.2.3 Base Impedance Measurements .2.2.4 Current Distribution Measurements .•••.••.•2.2.5 Field Distribution Measuremeilts .......•...2.2. 6 Corona Study .•...•...........•...........

2.3 Scale Model Factors ...•............•.•....••...••2.4 Calibration .................•....................

2-·12-12-12-12-42-6

2-82-102-112-11

3.

4."

o n uResonant Frequency Tests ..................•..........•.3. 1 Techniques .. '.f'j,' ••••••••••••••••••••••••••••••••••

3.2 Description of Tests .•.••.•.•.•.•.•••.••••.•••....3.3 n :;rest Results ..... '1 •••• "••••••••••••••••••••••••••

Antenna Selec'tion ..............................•.•....4.1 "Cost-Performance Study 0••...

3-13-2

t; 3-2o 3-4 0

4-14-2

lJ

o

ti ;;;6

eQ

c

°

5.

•

Antenna Mci'fiel Study' .........•...0,0 •••••••••••••••••••••

5. 1 Initial Configuration ..•..•.•• :: •.•••.•0•••••••••••••

00 05. 1. 2 Transmitter h-IeTix Building ....•....•..• ! ..o 5 1 3 B h' '~ ..." us lng ~ C!••••••••••••••••••

5.1.4 Downleads ..•.••..••.•..••.•••# •••..•••••

5.2 Evaluation of Initial Cor?figuration b ••.•.•.•••.•••••

5.2.1 Five-Panel (Emergency) Perfo~mance .o!!> 5.2.20 Six-Panelo(Normal) Performance ....•. : ..••

5.2.3 Gradient Distribution ..............•.•....."5~3 Development of Final Configuration •••••••...•••.•.

5",3.1 Revised Transmitter/Helix Building .......•5.3. 2 Revised Top Hat Shape , .5. 3. 3~ Revisecf'l'ower Heights ....•..••.•.•.•.•.••5.3.4 Wind Distortion Study .. ',,: ..:: •....... ~ .....

Summary of PrediCted Performance ., ..........••••....•

iii

5-15-15 -2 IV 0.'

5-2 ~

Ji;

5-75-75-7

5-11 €i

5-13 w

5-15 05-15 0

'!;- 2 05-275-30

eQ. (jo

6- 1

Page

Appendices

A. Model Data,.

A-1........ ....... .......B. Performance Relationships

r. B-1C. Antenna Equivalent Circuit C-1D. Investigation of V,LF Field Distribution D-1E. Photographic Corona Study .. .. .. E-1

"n

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o ILLUST RATIONS

Elevation View of }ongitudianl Panel Cross• Secwon as Modeled - Top Hat I .

o 0 0

Initial Transmitter /Helix Building ...........•.

Downlead Details ... : ...•...•.•..••.•.....•..o

Measured Base Reactance .. 5-Panef Operation'0 " 0o 0

Measured "Base Reactance - 6-Panel Operationg •

OCIradien1j.lf,)istributiPn on Top Hat I Panel •......•• Gradient Distributi~non Downlead - Static~

• C 0. ..onclltlon ............••...................9,.

Revised Transrnitfer/Helix Building .~

g

Ffgure 5..40

.Figure 5-5'0

'0

• Figure 5-6• 00 0

of' 5-719ure00

0 Figure 5-8

o •Figure 5-9

o·0

Figure 5-10

.,

Figure 2-1

Figure 2-2

Figure 2-3

"Figure 2-4

" Figure> 2-5

Figure 3-1

Figure 3 -2o °Figure 3-3

0

Figure 3-4

" ,0

Figure 4-10•

0

Figure 5 -10

Figure 5-2

0 FigJ're 5-3

00

o

Downlead Configurations - Test 1 throu~ 4 • d ••0

Downlead Configurations - Test 5 through 8 • • •0.

" 0

Downlead Configurations - Test 9 through0 12

o °Block Diagram of Equipment for Antenncf CurrentDist;ibution Measurerrlents ..........•.•.....•.

o

Equipment Block Diagroam for Base ImpedanceMeasurements 0••••••••0•••••

o

oTypical Downlead Configuration ShowingPertinent Dimensi)lns of PEt{ Version ..

° 0 0

Equipment Block Diag~m for Static CapacitanceMeasurements .••••..............•.•.•..•.. " •

V LF Model Range .............•......•.•.•...

Equipment Block Diagramjor Effective HeightMeasurements ....•...•....••.•......•••.....

Cost··Performance DatagRelating to Antenna 0

Sel~tion ...........•..........•.•...........

Plan View of Typical Panel ...•..•.•... ~ .o .' 0

Elevation View of Long!tudinal Panel Cross. 0

Section 0... Top Hat I • "0· 0" •••.•.

o

•

°

o

o

o

•• co0

0 f"

" C V

c

Figure 5-11 Measured Base Reactance at Two ReferencePoints .•..... '0' ••••••••••••••••••••••••••••• 5-19

Figure 5-12 Pictorial Schematic of Modeled Tuning/CouplingCircuitry at 28.5 Kc".•.•............•• : .•• : ..• 5-2 '1

,)

Figure 5-13n

Photograph of Modeled Tuning/CouplingCircuitry Viewed from Beneath T /HB .. ',,' •..... 5-22

o

o

o

Figure 5-14 Measured Ba~e Reactance Including Tunihg/Coupling Circuitry .......•.•...•.• " ....•...•.

Figure 5215 0 Elevatio~View of Longitudinal Panel Crosso Section 0_°Top Hat II .

5-23

5-24

o Figure 5-19

o

Figure 5-25

oFigure 5 -260> Q

CI

o

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o

o

o

o

5-31

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5-29

5-26

5-28

5-34

5-32

5-35

5-36

5-42

5-39

~37

5-38

•o

~vi

00o

oG

o@

o

Elevati~n View of L'bngitudinal Panel CrossSection CJ.s Modeled - Top Hat II ..•....•......•.

II 0 u

Elevation ,:view of Longitudinal ciPanel CrossSection"- Top Hat III .... 0•••••••••••••• ? ...•.

o

Elevation View ofoLongitudinal Panel CrossSection as Modeled - Top Hat III o' ••••••••••••0.

Measured Rase Re~ctance at Two Reference 0

Points 0•••••••••••••• '0' •••••••••••••••(0: 0

Plan Vi~w'of Antenna under Maximum WindDistortitiln ........•.•.........•.•.•...•..••.

{j, @ 0 0

Plan View of Panel 1 under Maximum Wind 0

Distorti~n ....•.... ~•..... :";........•........(~

PlaneViewC'llof Panel 2 underrJv1aximum Wind,0)

Distortion .•...•(j!l •••••••••••••••••••••••••••@ (i)

Plan View of Panel 3 under ~~imum Wind• 0. (i) It>

Dlst.orhon ...• ~..... '@ ••••••••••••••••••••••

(gJ ~ @Panel 1 Fan Downlead under Maximum Wind

oDistortion @

Pan~l 2 Fan Downlead under W~d DistortionCOJ \!Ii ~

Panel 3 .I!·ariQ·J.)ownlea~ under~aximum WindI.Distortion .....•..•...•.•...•••.•.•...•...•.

'.'0 0 0Measured Btlse Reactance for Top Hat III 0

under Jv1aximum Wind Distortion ..............•

Figure 5-24

Figure 5-27

°

o

o

Figure 5-20

& 0

C/o,

o

o

Figur~ 5-16

Figure 5-23

Figure 5 .... 18

Figure 5-21

Figure 5 -22

Figure 5-17

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Page

~;-45

5-46

5-47

5-48

5-49.p

5-50 IJ' .(1CO)

5-51@

@

5-52

5-53

6-3@

B-4

Gradient Distribution under Maximum Windon Panel 1 (Wires 1-4) ... 0 ••••••••••••••••••

Gradient Distribution under Maximum Windon Panel 2 (Wires '1-4) ..

Gradient Distribution under Maximum Windon Panel 2 (W~ires 5-8) .....•....•.•.•.....•.

Gradient Distribution under Maximum Windon Panel 1 (Wires 5 -8) ......•..•••.•.•..••..

Figure 5-32 Gradient Distribution under Maximum Windon Panel 3 (Wires 1-4) 00" 0 ••• 0 • 0;:,' 0-: •• 0 ••• 0 •

b '!f:i'

Gradient Distribution under Maximum Windon Panel ~ (WireR 5-8) .....\91 •••• ~J•• 0 0 ., 0 • 0'"

o 0

Gradient Distribution on Critical (No.2 Fan) @

Downlead untier 130 MPH Wif?d 00 •••••••••• 0 ••

'''Gradient Distribution(Q)on®Critical (No~ 2 Fan)Downlead under 110 MPH $ind .•.. 'S\l•• 0 •••• 0 ••

~. @@Gradient Distributiori on eritical (No. 7._ Fan)

(OJ '0) fA) ~

Downle'ad under ~~ MPH Wind 0 •••••••• 0 ••• 0 ••

(0)

Dase Reactance as a Function of Frequency. 0 ••

Basic Equivalent Circuit .

Incremental Section of a Long Conductor @

Showing Cylindrical Co-ordinate System(p, cp, Z)<9J " •••••••••• , •••••••••••••• ~•••• !'.

(!!J @BaRic Equivalent Circuit ................••..•

R~fined Equi~alent Circuit Including Near-Base Capacital?ie@..............•.... ,c9l ••••••

@Derivation of~quivalentCircuit @ ••••

@

@H-Field Distribution inll:he Vicinity of@Transmitter /Helix Building ......•...........

Figure 5-29

Figure 5-31

Figure 5-30

Figure 5-28

Figure 5-33

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Figure 5-34\0, 0;

Figure 5-35

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Figure 5-36(0)

(0)

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Figure B-1

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~~igure C-1

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Figure C-3

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. @FIgure E-1

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E-Field. Distributi0i>i~t~le Vicini~ ifTransmItter /Hehx BUllding ~ .@Antenna Model under Static Condition wit}e64 K E

_l . ,.., (I) '0,v XC Itationo .

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Figure E-2 Antenna Model unde'r Maximum WindDistortion with 30 Kv Excitation ..........•.•. E-5

Figure E-3 No.2 Panel Downlead under MaximumWind Distortion with 30 Kv Excitation E-6

° TABLES

(Q)

©

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Table 2-1

Table 3-1

Table 5-1

TiRlle6-1

TableA-1

Jable A-2

Summary of Calibration Data 0 •••••••••••••••••o

RePsonant Frequency TestResults ........•.....~

Parameters and Perfonnance of InitialConfiguration .........................•....•.

Jummary of Performance ........•.•.•...•....@

Model Data Summary .••...•...•.•............

MeasJ\ed Base Impedance (Referred to Full-Scale ~tenna) .

2-13

3-8

~

5-9

6-2

A-2 @@

A-3

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SYMBOLS (MKS Units or as Specified)'0

Electrical Symbols:

Ei = Incident electric field strength (volts/meter)

E, = Gradient at conductor surface (kv/mm)

o Incident magnetic field strength (amps /meter)(!},

ho Effective height (fcct or meters) @

fa = Resonant freq~ncy (kc)@ @ @

R o Radiation resistance (ohms) @ @@

@ @

§l @ Co = Effective antenna capacitance (f.Lf )

C.. =: Near-base capacitance (f.Lf)

Cs =: Static antenna capacitance (f.Lf) ::: Co + C ..

L o@ @

= Effective antenna inductance (p.h)

@

Antenna Parameters: @

@

K1 '"@ @

~ @ h =:

V. =

@

@

@

@

©

@

@@

@@

@

@

@ @@

@@ @ (;)

@

Base voltage of antenna (volts)

Top hat voltage (kv)

@

Ratio of monitol" base voltage fo the field incident on

the ~odel ::: (V. /Ei )@ @ @

Physical he~ht of thin monopol, used in range calibration

Base voltage of E-field monitor antenw- (volts)

@ . ~@ ~

s

Vt

10 = Antenna base current (amps)

z .. , x .. = Antenna base irnp~dance, reactance (ohms)~ @

bwo = Bandwidth of theoreticallossless antenna (cycles)@

a =@Aspect ratio (tower height/top hat span)@ @

"'@Similitude scalIng factor to be applied to all dimensions@ @

Calibration:@

@

@

Range

@

o 0o o o

o

(0)

1. INTRODUCTION

This report presents information developed in the scale model

study of the high-power, very-Iow-frequency (vlf) transmitting antenna

for the U. S.. Navy V LF Communication Facility, Pacific. The study is

an integral pa'rt of the final design effort under Contract NBy 37636 be-

tween the-U. S. Navy Bureau of Yards and Ducks antI the Juint VtutU!'C

firm of Holmes & Narver, Inc." Continental Electronics Manufacturing

Company, and DECO Electronics, Inc. (HNCD).

The basic configuration of the antenna system under study was

chosen in the Plbeliminary Engineering ]{eport (PER) phase of the project.

Thi.s phase was carried out by the Jomt Venture firm of Developmental

Engineering Corporation (later, DECO Electronics, :rnc.) and Holmes &:o 0 0

Narver, Inc. , undel' Bureau of Yards and Docks Contract NBy 37598.

Supplement 1 of the PER, Sing~~o<!~ie~~u_t1erAntenna_~d VLF An­

tenn Comparison, presented the recommended configuration based on

cost and performance data for a single-element antenna approximately~ ~ a

28 percent larger than the Cut1ef:l.~.-type element. Further studies carried(0)

out under Change Order F' of Contract NBy 37598 provided cost-trade

information relating to the aspect ratio (relation of top hat spans and@ (Q) 0

tower heights) and structural alternatives such as halyard slope, canti­~)

lever length, etc. 0

From c~nsiderations based on the PER, an initial choice of major@ 0 •

antenna dimensio~was ~tablished. The purpos.,.,f the 1t0del study

@ d~cribe~n this report is to present a detailed summary of the electri­

cal(\)~erformance dataoIerived from a 1: 100 scale model of the initial 0

antenna and of the subsequent lTIodifications leading to a Rnal des'gn.(\))

(Q)

.~ ~)

~ ~

0

0

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0 00

CtC

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0

00 0

1-1

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2. TEST PROCEDURES

2. 1 Mode I Range

The model range used in this study is a modified version of the

one used in the PER modeling program. \See Appendix E of PER. )

An increase in the size of the antenna over that of the Appendix E

studies required an extension of the ground plane (as shown in E'igure

2-1). To increase the accuracy of effective height measurements, it

was necessary to install an E-field monitor consisting of a short mono-

pole off the south end of the range. However, because of scheduling

considerations, the resonant frequency tests were performed before

the E-field monitor was calibrated. These earlier testa employed the

H-field monitor used in the PER test series.

2.2 Equipment

Except for the E-field monitor and current distr ibution probe,

the equipment u~ed in this work was identical to that used in the PER

modeling.

2.2. 1 Effective Height Measurements

Figure 2-2 is a block dlagram of the equiplUent used in the

effective height measurements. The figure illustrates the use of the

E-field monitor employed in most of the work. However, some earlyo

work in this stuely used the H-field monitor (RCA type WX-2C Fieldo

Intensity Meter) as described in the PER. Tn using the E,-fielcl moni-

tor, the same receiver·-voltmeter combination was employed to incli-

cate both the incident field (as indicated by the monitor base voltage)

o

o

and the base voltage of the vlf antenna model under test. Both then

•

monitor and the test antennas were terminated in low-input-capacitanceo 0

cathode followers to reduce loading effects. 1n either case, theo

oo

o2-1

" 0

o 10 10 3u 40••

81' - -

69'

DECD 43-21 63~318 D

00 KC SICNAlSTOWARO 1500, 16 0 CWASHIHGTON•••

SCALE

VLF MODEL RANGEFigura 2-1

oo

2-2

DECO 43-21 630318 C

IIL _

IIIIIIII

_ _J

E- FI ELO

PRESSURIZEcr calX FRaN MJNITcrREJU I PMENT ROO~ TO RENOTE j

"' NONITOR· . .?~~~~n · -~~/VlF ANTEN~1

MOcrEl

r-------l

: EQUIPMENT ROOM UNOERo:I NcrOEl ANTENNA IL J

IIII

01

r--­II[

[

4) I

o

o

-~""7)/""'7"~"9""2Z$;-n,,'3'Tf1~

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I

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l(l;lLl

o

Figure 2-2 EQUIPMENT BLOCK DIAGRAM FOR EFFECTIVE HEIGHT MEASUREME~TS

measurement consisted of tuning the receiver (R-j~OI to the local broad­

cast station (WAGE, 1290 kc) and observing a reference voltage on a

vacuum tube voltmeter (Ballantine 300) monitoring the receiver i-f out·­

put during a period of no modulation. Then, the signal generator (CR

1001A) output was substituted for the antenna at the cathode follower

and adju.sted to give the same reference indication in each case. The

actual recorded voltage was indicated by a calibrated rf voltmeter \HP

400H) across the signal generator outpuL

This technique uses the same procedure for measuring both the

incident field and the base voltage of the antenna under test, thus as"

suring the same degree of accuracy in both measurements.

2.2.2 Static Capac itance Measurements

Measurements of static capacitance were accomplishp.d with the

equipment arrangement shown in Figu:t:e 2.-3. Static capacitance is de··

fined as the apparent capacitance at the antenna tenninals as the he·o

quency approaches zero. It is sufficient that the test frequency not beo

greater than a few percent of the resonant frequency for the purpose

of measurEi,ment.oln this case, resonance occurred near 3.0 mc, and

static capacitance was measured at 30 kc (i. e., 1 percent of resonant

frequency). The actual rneasurernent involved a high.-Q, pal'allelreso-

o nant circuit em.ploying a high-Q work coil, and a precision variable

capacitol" (GR 722). The antenna was connected in such a way that its

o capacitance appeared in parallel with this circuit~ The va.riable capac i·-

tor was then adjusted to bring the circuit to resonance as indIcated on

the rf voltlTIeter. The capacitor setting at resonance was recorded.

Then the antenna was removed frorn the circuit and the capacitor again

adjusted to restore resonance. The difference between the two capaCI'

tor settings w~s determined to give the static capacitance of the antenna.

2-4

o

I DECO "-21 """" II .. I

VOLTMi:TER(HP 430H)

\\\\\\

---= /, • '

~CISI"M V.::::lECAPACITOR (GR 722)

-

\-\'\\'\\( COUPLiNG\ \\ CAPACITOR

VLF /lOOElANTENNA

OOWNLEAD

GROUND SCH EEN"""""

30 KC

SIGN AtGENERATOR

(HP 200CO)

• 0

0.,

r·(\J

IU1

Figure 2-3 EQUIPMENT BLOCK DIAGRAM FOR STATiC CAFACITANCE MEASUREMENTSI

It should be noted that the static capacitance measurement does

not indicate the distribution of capacitance within the circuit. It is con­

venient to consider the top hat as the Inain capacitor elenlent. However, a

significant portion (5 to 10 percent) of the static capacitance results from

the downleads and appears to act on the ground side of the antenna induct­

ance. This effect cannot be seen without complete impedance data over

a wide frequency range, including the region around resonance.

2.2.3 Base Impedance Measurements

Base impedance measurements between approximately 1 and 4 mc

were obtained with the equipment shown in Figure 2 -4. The nieasuring

instrunlent used was a radio-frequency inlpedance hringe iGR 1hOnA). A

signal generator (GR 100 fA) provided the drive signal, and a receiver

(R-390) with a voltnleter (Ballantine 300) nlonitoring the i-f output pro­

vided the null indication. Frequency calibration was established by com­

parison with WWV and at intermediate frequencies by use of an electronic

counter (HP 524).

The Ineasurenlent point for base inlpedance was at an opening in

the model Trans mitter /Helix Building floor ju s t below the bushings. A

ghort vertical lead provided the path froIn floor to bushing. Later,

nleasurements were made directly at the bushing entrance point to deter­

nline the inductance of the inserted lead, using the top of the corridor

dividing wall as the ground return ternlinal.

Resonant frequency was established by repeated impedance

meaSurenlents in the region of resonance.

2.2.4 Current Distribution Measurements

The distribution of current over the antenna (top hat and down­

leads) was accornplishecl with the use of a small, electrostatically

2-6

HELIX HO'SE~

"OUNO SCREE~

\\

DECO 43-21 630318 A

, ( ( ( ( {

NI-.J

SIGN AtGENERATOR(GR 1001A)

RF BRIDGE(OR 1606A)

RECEIVER(R-390),

I

l'FVOL THETER

(BALLENTINE 3DO)

Fi gure Z-4 EaUI PMENT BLOCK DIAGRAM FOR· BASE IMPEDANCE MEASUREMENTS II ~

shielded oscillator positioned along the various conductor s as shown in

Figure 2-5. The oscillator probe consisted of a self-contained 1560 kc

crystal-controlled transistor oscillator with a small coupling toroid,

all (except for a small break in the toroid shield) encompassed by an

electrostatic shield. This device, loosely coupled to the antenna con­

ductor under test, was passed along each conductor, and the receiver

(R-390) i·-f output was monitored with an rf voltmeter (HP 400H). Before

and after each conductor test, the probe was coupled to the bus at the

bushing entrace point for a reference reading.

To establish proper operation of the probe oscillator, a short,

thin monopole was constructed, and current distribution rneasurements

were made using the probe. Since the current distribution on such an

antenna is well known (i. e., linear), it is possible to obtain a good

check on the probe performance.

2.2.5 Field Distribution Measurements

In the area over and around the Transmitter /I-Ielix Building

(T /HB), both E·· and rI·-field measurements were made on the antenna

model. These meaS\l1'ements were made with sman probes (loop for

magnetic field, capacitor for electric field) connected through coaxial

cables to a sensitive receiver (Stoddart NM-20B). This type of meas­

urement requires careful orientation and positioning of the sensing

device and adequate shielding to avoid stray pick-up. The receiver

provides an indicatIOn of only relative magnitude, and the data must

be normaliz.ed to a known reference value. Two types of reference,

or calibration, were used;

(a) The magnetic field probe positioned at the conducting sur­

face of the Tr ansmitter /Helix Building (T /HB) or nearby ground screen,

2-8

DECO 43-21 630320 B

CENTER lOWER

INDUCEDCURRENT

I-

V)V)...'"co

PROBE DETAIL

ANTENNA ~ 1.-112"CONDUCTOR

LOOPSHIELO

RFVOLlMElE R

<HP 400 H)

TYPICAL POINT AT WHICHCURRENT <RELATIVE TO BASE)IS TO BE OETERMINEO.REFERENCE POINT ON OOWNLEADBUS ON T/HB ROOF.

Figura 2-5 BLOCK DIAGRAM OF EQUIPMENT FOR ANTENNACURRENT ~ISTRIBUTION MEASUREMENTS

2-9

measures the tangential H-field component. At the surface, this com­

ponent is identically equal to the surface current density. Calibration

consisted of measuring the relative tangential H-field (i. e., surface

current density) at several points a short distance from the bushing

entrance point. Integrating the radial current density around a path

enclosing the bushing entrance yields the total base current. Other

readings were then referenced to this value.

(b) The capacitive E-field probe was calibrated by positioning

a short distance apart two ITletal sheets, large with respect to the 1­

inch probe, and providing rf excitation at the test frequency. For large

plates rlosp.ly spaced, the field is uniforITl over most of the interior and

is equal to the ratio of the iITlpressed voltage to the separation. This

calibration yields a proportionality constant which, when the actual base

current of the antenna ITlodel is measured, allows each relative E-field

reading to be referenced to an absolute value.

2.2.6 Corona Study

Qualitative data on the distribution of charge on the antenna was

obtained by applying high voltage (up to approximately 60 kv), 60-cycle

excitation to the model at night and photographically recording the oc­

currence of corona by ITleans of long exposures. These photographs,

taken at progressively higher voltages, show the critical regions where

corona first appears, and can be correlated with indirect methods of

gradient analysis (i. e. , current distribution). Since the cntical gradient

for corona forrnation is a non-linear function of the radh.ls of curvature,

the direct scaling of corona onset voltage is not possible (see Appendix

E). However, the capability of directly observing the entire antenna

(or a characteristic part such as one panel) at corona onset is highly

useful in confirming the indications of the alternate method.

2-10

2.3 Scale Model Factors

For all of the lllodel work, a scale factor of 1:100 was elllployed.

To convert to full-scale data, the lllodel data is lllultiplied by the appro­

priate scaling factor below:

Parameter Scaling Factor

• Effective Height (and all 100other distances)

• Capacitance 100

$ Inductance 100

$ Frequency 0.01

• Radiation Resistance 1 (at scale frequency)

• Base Impedance 1 (at scale frequency)

To model the ohmic cOlllponent of the resistance, it would be

necessary to scale all conductivities 100 times greater than the full­

scale values. Since this is obviously illlpossible, no attelllpt was made

to use base resistance data frolll the model.

2.4 Calibration

The purpose of the model range is to provide a relatively large,

smooth, highly conducting plane over which the incic1ent radio-frequency

field propagates unperturbed by discontinuities and reflections. In

practice, this can only be approximated because some variations in the

surface characteristics still relllain which cause 8111all variations of the

incident field over the area of interest (i. e., the region around the test

antenna, including the monitor antenna which measures the incident

field). Therefore, it is necessary to perforlll calibration measurements

to determine the relation between the incident field at the monitor and

at the test antenna.

2-11

Effective height measurements were accomplished by comparing

the open-circuit base voltage Vb with the incident field strength E 1 at

the :model:

meters. (2 -1)

Since the incident field at the model is not necessarily equal to

that at the :monitor but in all cases is directly proportIOnal, the effective

height may be expressed as

meters , (2 -2)

where Vm = monitor base voltage, and K1 = range calibration constant.

The determination of the .r:auge calibration constant K 1 in Equation

2-2 was made using several short. thin monopoles of known effective

height. For a thin monopole, the effective height (ho ) is simply related

to the physical height ~ by

he =h/2 (2 -3)

Depending on the thicknes s of the monopole and on the near-base or in­

sulator capacitance, the actual effective height may depart from half the

physical height by as much as several percent. However, by a proper

choice of diameter and base insulator configuration, the difference be­

tween Equation 2-3 and the actual effective height may be reduced to a

fraction of a percent.

For the calibration tests seven monopoles were employed. A

specially tapered 3-meter monopole was constructed to have uniform

capacitance per unit length,as suggested by SchelkunofL 1 In theory,

1 Schelkunoff, S. A •• and H. T. Friis. Antennas, Theory and Practice.New York, Wiley. 1952. P 318, Figure 10.9.

2-12

this element has an effective height equal to exactly half of its physical

height. However, some uncertainty about the near-base capacitance led

to the use of cylindrical monopoles of various lengths all utilizing the

same base configuration. Since the same near-base capacitance was

present in each monopole of this calibration series, an empirical deter­

mination of this parameter was possible through the correlation of the

measured effective height data.

Table 2-1 summarizes the range calibration data. The effective

heights shown are the assumed values of one-half the physical heights.

The ratio of monitor voltage V m to base voltage Vb corrected for near­

base capacitance loading effects is as shown in the table at 1290 kc for

all te st rrlOno pole s.

TABLE 2-1

Summary of Calibration Data

EleITlent Element Effective RangeLength Diameter Height V m /Vb Constant(feet) (inches) (meters) (K1 )

9.85 tapered 1. 5010 .6724 1. 0093

9.85 1/4 1. 5010 .7143 1. 0722

9.00 1-1/ 8 1. 3'716 .7656 1.0501

1£'..00 1-1/8 1. 8290 .5690 1. 040'7

15. 00 1·· 1/ 8 2.2860 .4621 1. 0564

18. 00 1-1/8 2.7432 .3823 1. 048'7

21. 00 1··1/8 3.2004 .32,86 1. 0517---

average constant 1. 0470

2-13

Since the ratio Vb /Vm is theoretically a linear function of the

effective height he, the last five monopoles (1-1/8 inch diameter) were

treated by the least- squares method to fit a line to the data. This

analysis yielded K 1 =: 1. 055. This value was used as the calibration

constant in the 1290-kc measurement of effective height rather than

the average value because more data was available to evaluate the in­

fluence of voltmeter (cathode follower) and near~base capacitance.

2-14

3. RESONANT FREQUENCY TESTS

An analysis of construction costs carried out under the PER

phase indicated that radiation system performance (primarily the

antenna bandwidth) could be improved without increasing the cost by

altering the aspect ratio and the similitude scale factor of the antenna,

Specifically, it was determined that reducing tower heights and in­

creasing top hat spans would result in greater bandwidth for the same

cost. The performance characteristics of various aspect ratios':' and

similitude scale factors':":' were determined from a model study carried

out under Change Order F of the PER.

The model study indicated, ho",."'~ver, that the self-resonant. fre­

quency of the antenna for the near-optimum combinations of aspect

ratio and similitude scale factor was marginally close to the 30-kc

upper operating limit specified for antenna performance. This in­

cluded some reduction in resonant frequency because of residual in­

ductance in the tuning and coupling circuitry at the high end of the

frequency range. Since it was not considered economically feasible

to use series capacitive tuning to provide for operation above natural

resonance, the U. S. Navy directed that this method not be used.

Therefore, other means were sought to extend the operating range

with inductive tuning. The method used to solve this problem was the

reduction of the aggregate downlead inductance by altering the configu­

ration or by employing more parallel conductors.

~:~ Aspect ratio ~ is defined as the ratio uf outer tower height tomaximum top hat span, normalized to the L28-Cutler dimensions.

':":' SiInilitude scale factor s relates all linear dimensions to the1. 28-Cutler design for unity aspect ratio.

3-1

Since the selection of final antenna dimensions had not been con­

cluded, the resonant frequency study was carried out on a 1: 100 scale

model of the 1. 28-Cutler configuration.

3. 1 Techniques

To increase the resonant frequency, several downlead configura­

tions were suggested which would alter the effective radius of the aggre­

gate downlead path (consisting of six identical cages or groups) with the

possibility of reducing the inductance. Since the downlead "bundle" was

roughly 700 feet in diameter and only 900 feet in length, simple analytical

approximations based on long, thin conductors did not produce accurate

quantitative results. However, for such simple structures the induct-

ance is proportional to the logarithm of the length-to-diameter ratio.

Therefore, it was expected that increasing the effective diameter of the

downlead bundle would result in the desired increase in resonant frequency.

However, it became apparent that the structural problems associated with

increasing the center tower-downlead truss separation were formidable.

For this reason several configurations were tested which employed a

variety of truss and hinge point locations as well as various numbers of

downlead conductors.

3.2 Description of Tests

Figure 3-1 is an elevation view of a typical downlead configura­

tion. Since the resonant frequency tests were undertaken at the start of

the final design contract and prior to the determination of the first Trans­

mitter/Helix Building configuration, the Helix Building design of the PER

was used for these tests; this version employed three bushing entrance

points each of which fed two adjacent panels. The dimensions lettered

(A), (B) I and (C) in Figure 3-1 are those which were varied and found to

influence the resonant frequency.

~-2

DECD 43-21 630320 A

~ INSULATOR AND GRADINGRING ASSEMBLY

TO P HAT

DOWNLEAO TRUSSCENTERTOWER

OOWNLEAD RI SER

1~--303'-~11II

HINGE POINT

HEll XBUI LOING

OOWNLEAO RISER AND HINGE-T/HB BUSCONSISTED OF FOUR I-INCH CONDUCTORSSPACED ON A 2.82-FT CiRCLE.

100 0.1. 100 200 300I

SCAlE - FEET

L __F_ig_u_f9_3-_J__TY_P_I_CA_L_DO_W_N_L_EA_D_CO_N_F_IO_U_R_AT,I 0N SHOW I NOPERTINENT DIMENSiONS OF PER VERSiON

3-3

For each downlead configuration, the effective height and static

capacitance as well as the base impedance were measured. Particular

attention was devoted to impedance Ineasurements near resonance.

Figures 3-2, 3-3, and 3-4 show the various downleads tested.

For all types of downleads and all positions of the downlead truss, the

elevation of the downlead truss was maintained approximately constant.

Tests 1 through 6 employed a 4-wire cage for the hinge··point­

to-·helix house bus; Tests 7 through 12 used a copper tube of approxi.­

mately equivalent inductance per unit length. Beginning with Test 9,

a completely new top hat replaced the earlier version which had been

damaged by wind. These changes inl.1·uuuceu very 1nin01 variations in

performance which were not related to the particular downlead cqnfigu-

ration involve d.

3.3 Test Results

Table 3- 1 shows the significant dimensions of the various down··

leads along with the effecti.ve height, E,tatic capacitance, and resonant

frequency. Also included is the unloaded or lossless antenna band­

width (bwo ) at the design frequency (15.5 kc) derived for comparison.

All data given is referred to full scale operation.

Initially, it was proposed that three downlead pulloff points

(1. e., A = 381, 481, and 581 feet in Figure 3-1) would be tested along

with various hinge-point locations. However, in implementing the

tests, it was decided that the intermediate (A = 481 feet) pulloff point

would be tested only after the extreme position (A = 581 feet) proved

effective.

The original goal for the resonant frequency was about 33.3 kc.

This was established by assuming a 10-percent reduction due to residual

3-4

Otto 13-21 U03l9 C

----------~

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/?/")"11S L't'~-__ _ I

--''''-------jI TEST'

381'

TEST 1

Tl$13

TESTl

--- ~BI'

T'"I

i

Figure 3-2 DOWNLEAD CONFIGURATIONS - TEST 1 THROUGH 4

3-5

.!to .H' """. I

l

~ - liRE CAb_

. I t4 ,,.. jt -

200'

l

TEST ~

~-- -----'

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. I t~-~._--J- lOL 1

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II ,"-

I '"' ".j r '''' ~

I

1"," 'II-

II

Ii jII · ' "" c.e, 7> ,_

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TE51.

-,

Figure 3-3 DOWNLEAD CONFIGURATIONS - TEST 5 THROUGH 8

3-6

~-'"!IIj .. . IIU CAIiE ~

II '

I 'I t,_.f( rI. 3D3' ..j

TEST 9

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TABLE 3-1

Resonant Frequency Test Results

A B C .AntennaTest D~wnlead Truss Hinge Hinge Effeotive Static Resonant BandwidthNo.

Vertical ~orizontalRadius Radius Elevation Height Capacitance Frequency at 15.5 kc(feet) (feet) (feet) (feet) (fif) (kc) (cps)

4-Wire Cage 4-Wire Cage 381 303 192 638 .1498 31. 50 36.4

2 4-Wire Cage 4-Wire Cage 381 (No Hinge) 640 .1487 30.75 36. 3

4-Wire Cage 4- \\tire Cage 581 (No Hinge) 638 .1499 32.05 36.3

VJI 4 4-',Vire Cage 4- \Vire Cage 581 505 295 627 · 1519 32.30 35.6

CfJ

5 4-Wire Cage 4-Vnre Cage 581 581 125 600 • 1561 32.18 33.5

6 8- "rire Fan 4 - \Vire Cage 581 320 200 643 .1530 35.10 37.7

7 8-V-.lire Fan Tubing 581 581 200 628 .1543 34.98 36.3

8 4- 'Vire Fan TC\bing 581 581 200 635 · 1531 34.47 36.8

9 Tubing Tubing 381 303 192 6-1,2 .1497 31. 68 36.8

10 s- \\tire Fan Tubing 381 303 192 635 .1514 33.27 36.3

11 4-'Wire Fan Tubing 381 303 192 634 .1506 32.87 36. 1

l1A Same as 11 with hinge pulloff 381 303 192 639 .1505 32.87 36.7halyard

l1B Same as 11 with O. 005 pi 381 303 192 635 .1554 32.87 37.3shunt in Helix Building

12 -I,-Wire Fan Tubing 381 505 200 631 .1521 33.05 36.1

tuning and matching inductance and a minimum upper operating frequency

of 30 kc. The exact effect of the residual inductance depends on tuning

component design, which was not refined at that time. Therefore, the

10 percent margin was tentatively established for this purpose.

The first five tests explored the various positions of the 4-wire

cage downlead (the full-scale version consisted of four 1- inch conductors

positioned at the corners of a 2-foot square). No combination of dimen­

sions in the range considered feasible was found which would yield the

desired resonant frequency. At this point, the cage downlead was dis­

carded in favor of a spread or fan arrangement to further reduce the

downlead inductance. Te st 6 employed an 8-wire fan downlead which

was positioned at the extreme pulloff point (A =.: 581 feet) and resulted

in a resonant frequency of 35.10 kc, well above the 33. 3-kc goal. Test

7 introduced an increase in the hinge-tower separation (B) from 320 to

581 feet; this produced a small reduction in resonant frequency to 34.98

kc. At this time, the structural problems associated wit}, this larger

separation requiring a very large downlead truss and the windloading on

the 8-wire fan dictated that further effort be made to reach a compro­

mise version which would be economically acceptable.

Test 8 explored the possibility of reducing the number of con­

ductors in the fan from 8 to 4. For the same A and B dimensions as the

8-wire fan in Test 7, the 4-wire version yielded a resonant frequency of

34.47 kc, a 0.51 kc reduction.

At this point, the model was damaged by ice and wind to the point

that further work required a complete replacement of the top hat. After

the new top hat was erected a control test (Test 9) was made to show any

changes that had been introduced in the top hat replacement. Compari­

son of Tests 1 and 9 showed essentially no change except for a resonant

3-9

frequency increase of some 0.18 kc over the Test 1 resnlts. However.

Te8t 9 rather than Test 1 was used as a :teferencE' fo'- Te5t8 10 through

12.

Tests 10 and 11 show the result of replacing the PER downlead

(Test 9) with fans of 8 and 4 wires, respectively, with the same A, B,

Rnn C dimensions. This resulted in an increase in the resonant fre

quency to 33.27 kc for the 8-wire fan, and to 32.87 kc ior the 4·-wil'e

fan. This result is marginal for the assumed 10 per cent 1 edl~etiof1 ek,e

to residual inductance, but does indicate the feaEiibility of the fan-·type

downlead as a means of increasing resonant frequency.

Tests 11A and 11B involved two ruinor chailges which weIe JuullIl

to have no measurable influence on resonant frequency. :tn Test 11A,

the hinge-point counterweight halyards and insulators were added. Test

11B introduced a small shunt capacitance;. 005 !.J.f full 8Lale) inside the

Helix Building across the antenna termir"als. Both changes should not

be expected to change the resonant frequency appreciably- since a voltage

node at the antenna base at resonance renders shunt elemeEtr,: Ineffective

at that point.

Test 12 shows the effect of increasing the R dirnension to 505

feet (mabng the downlead slope away from the tower' base) in a ma:.1ncr

suggested by the structural designers. This produced a slight iLclease

in resonant frequency to 33. 05 kc, O. 18 kc above the value for Test 11.

Since Tests 11 and 12 both employed 4··wire downleads, some further

increase could be predicted fOl' the 8-wire fan in tLe Test 12 configura­

tion. Comparing Tests 7 and 8 and Tests 10 and 11 shows an average

increase in r.esonant frequency of 0.45 kc for the 8 oveJ the 4·-wire fan.

Extrapolating Test E. r'esults on this basis yields a predlc1:erl re:;onant

frequency of 33.50 kc for the 8-wire fan in the Test E conIigm ation.

This value safely satisfies the 33.3 kc goal.

3-10

4. ANTENNA SELECT:;ON

The initial configuration of the vlf antenna to be modeled in the

final design phase was developed":' through the consideration of the various

design constraints of cost, pel'formance, reliability, etc., in relation to

analytical data developed in preliminary studie s of structural and elec·­

trical p.i'operties of various alternatives. Specifically, lIluuel ~tLHlie~':"':'

provided information on the variation of electronic perforrnance with

structural variations of the following types:

(a) Size and aspect ratio of the antenna III comparison with the

1. 28 CQtler design.

{bi Downlead configuration.

(c) Halyard slope, tower cantilever, and "B" tower.-height

compensation.

During the development of the final design, the various cost and

performance constraints were continually reviewed to take advantage of

every opportunity to improve performance or to reduce cost as a result

of design trends established in the preliminary phases of planning.

':' Further details on the selection procedures are contained in HNCDletter of '7 february 1962 to GiG, "VLF Pacific Antenna Selection" andan HNCD report "Basis of Selection of VLF' Antenna Configuration,"April 1963.

'i';' Basic antenna studies relating to the 1. 2.8 Cutler design were per ..·formed under Contract j\[By-37598 and presented in the PER. Specificstudies of the effects of halyard slope, cantilever length and B tuwercompensation, together with size and aspect ratio studies, were ac­complished under Change Order F of that contract. The effect of down·lead configul'ation on resonant frequency was explor ed under the earlyphases of Contract NBy .. 37636; the results are presented under Section3 of this report.

4-1

Particularly, it was recognized that the achievement of optimum band­

width was not compatible with the originally specified upper operating

frequency of 30 kc without employing additional capacitive tuning cir­

cuitry. Consequently, by direction of cognizant Navy offices, a revised

minimum upper operating frequency of 28.5 kc was established.

4. 1 Cost-Performance Study

Based on the final phases of the PER and early studies in the

final design program, the modified Cutler design was selected with the

following provisions:

(a) The size of one Cutler-type element was increased by

a factor of 1. 28 to provide adequate bandwidth and power radiating

capability.

(b) Vertical halyards were employed and cantilever lengths

were reduced to 10 feet, requiring an increase of 45 feet in the inter­

mediate tower heights to compensate for the cantilever reductions.

These values depart from corresponding PER conditions of

sloping halyards, 57-foot cantilever, and 57··foot compensation, but

provide roughly equivalent electrical performance.

Considering both structural and electrical aspects, the antenna

recommended for final design was conE-idered to have the greatest

potential of meeting the requirements summarized below:

(a) Antenna bandwidth (100 percent efficiency) not less than

37.5 cycles at the design frequency of 15.5 kc.

(b) Upper operating frequency not less than 28.5 kc.

(c) No tuning capacitors required to meet (b) above.

(d) Estimated cost not to exceed that of the Single Modified

(1:28) Cutler Antenna.

4-2

Figure 4-1 SUInmanzes the data developed for the cost-perfonn­

ance study relating the antenna bandwidth and resonant frequency to the

siz.e, aspect ratio, and cost. The data of Figure 4-1 is typical of the

inter-relations considered in arriving at a final configuration. Since

bandwidth occupies a dominant role in the antenna selec tion, this factor

is emphasized. Considering the bandwidth and cost constraints, the

acceptable combinations of ~ and ~ in Figure 4-1 are seen to lie in the

region above the 37.5 cps line and below the PER cost line. The n,axi·­

murn antenna resonant frequency in this region was about 30.6 kc for the

PER design (4-wire cage downleads), which yields an upper operating

frequency of only about 27.5 kc with the 10 percent tuning and coupling

margin.

Having recogni:<,cd the resonant frequency pr'obleH1 prior to the

start of the final design, the resonant frequency study (Section 3) was

undertaken to develop means of increasing resonant frequency without

degrading other performance aspects. For the modified 1. 28 Cutler

configuration i~ =.~ = 1), the 8-wire fan downlead resulted in an increase

in resonant frequency of approximately 5 percent over the value obtained

with the 4· wire cage downlead in a similar conliguratlOn. Estimates

were made of the effects of the deviation from unity aspect ratio and

scale factor which, together with a 10 percent margin for the tuning­

coupling effect and 1 percent tolerance lim~t, located the 111aximum

operating frequency \28.5 kc) line on F igllre 4-1.

Considering the three constraint lines (cost, bandwidth, maxi­

mum operating frequency) in Figure 4-1, the point for _<:. = 0.925 and

~ = 1.05 determined the antenna configuration recommenueu uy I-INCD.

This choice provides for adequate bandwidth (with no safety margin)

and maximum operating frequency at an estimated cost not greater than

4-3

I. 00

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..........~ .

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28.5 KC ESTIMATED MAXIMUMOPERATINQ FREQUENCY FOR8-.WIRE FAN DOWNLEA~~ j

,10,! COUPLIN!.l!~TO~

.85 .90 .05

DECO 43-21 630413 TH A

~l ------z::-.::.".--

.., _~~ I,":' /---- ~ ';:'Nl'OO'RESONANT1/"0 ..--:: .~. 'l0'~... FREQUENCY WITN 4-W1

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a - ASPECT RATIO

Figure 4-1 COST-PERFORMANCE DATA RELATING TO ANTENNA SELECTION

4-1

that of the PER design. The decision to delete a safety margin to

account for prediction tolerance in the bandwidth parameters was rnade

with the concurrence of cognizant Navy offices. The recomm.endation

was predicated on the inclusion of a bandwidth control element in the

transmitter which could compensate for a minor degradation of antenna

bandwidth with some attendent reduction in efficiency, The recom­

mended configuration was accepted by the Navy and modeling pro­

ceeded on the basis of this selection.

4-5

5. ANTENNA MODEL STUDY

5. 1 Initial Configuration

As a result of the antenna selection study iSec.tion 4), the antenna

configuration initially constructed for further model study in the final

design stage differed from the previously modeled PER design (1. Z8

Cutler) in the following aspects:

(a) The aspect ratio ~ and similitude scale factor ~ were changed

from unity in the PER version to a = 0.925 and s = 1. 05 for the initial

configuration. These changes resulted in towers approximately 25 per­

cent higher and spans approximately 35 percent greater than Cutler.

(b) The tower heights were further increased to maintain the

average height with the non-counterweighted top hat and the corl'esponding

increase in sag.

(c) An 8-wire fan downlead replaced the 4·~wire cage previously

used.

(d) The downlead hinge point was positioned at a 500-foot radius

from the center tower and elevated 186 feet above ground.

(e) A combined Transmitter /HeJix Building replaced the PER

helix building at the base of the center tower. Also, the tower was nested

in a well in the building rather than directly on the roof.

(f) The busses combining the downleads at the Transmitter/Helix

Building were external rather than internal as in the PER design. These

initially entered the building through a single bushing rather than the pre­

vious three.

(g) Initially, the internal circ uitry was not irlstalled in the tuning

and coupling area of the T /HB. A short vertical lead simulating a 10-inch

5-1

bus provided a convenient measuring point at an opening in the rnodel

l' /HB floor.

Figure 5-i shows a plan view of a typical panel of the top hat.

As initially proposed,the panel consisted of four outer conductors (Nos.

i, 2., 7, and 8) of aluminum clad (approximately 7 mils of aluminum)

IloII1.illally i-inch outside dian~eter cablc, whereas the four inner con­

ductors were of i-inch ACSR Ii. e .. with a solid aluminum outer lay).

Also, the outer two conductors of each side were enlarged to 1-1/Z

inch diameter in the region near the intermediate towers. The ACSR

conductors were proposed where structurally feasible in an attempt to

reduce losses. Figure 5-2 shows an elevatLOn view of a longitudinal

panel cross section with an exaggerated vertical scale to emphasize the

sag. For the model version,each catenary was approximated by estab··

lishing two sag points as shown in Figure 5 ·-3. This top hat (designated

Top Hat :I) has a centroid elevation of 900 feet.

5. 1. l Iransmitter /!!:~!~~_l?_~ld~~!2.

In the proposed design, the transmitter and the tunmg/coupling

circuitry wer e housed in the same structur e (1' /1113). This eliminated

an extensive transmission line as well as provided other structural

ecoI1Olnies. Figure 5~4 shows the external features of the l' /HB aH

initially proposed. The center tower was placed in a well approxin~ately

:',5 x 40 feet in the building. The model version of the building was made

of sheet brass and included the tower well and the internal switch rooms

which form a corridor beneath the bushing entrance area.

5. 1. 5 l?ushinl2.

The T/HB shown in Figure 5··4 used only one entrance bushing

instead of three as in the PER verslOn. At the beginning of the study,

5 ·-l

DECO 4~·21 630319 F

r-- 2002.3!1' '.. 2124.15' ;:JI

OUTER PANEL INNER PANEL

.1&8.46' • 1833.89' la3~.S9' 290,26' ,

I I

! t It "6" TOWER I I

U1l

VJ

SYMMETRICAL.

ABOUT 'to

LENGTHS (PLANIOF CONDUCTORS

taB 2117.21

2 a 7 2081.93

3 a 6 /947.73

4 as 1847.24,

IO~I.6· CF 1'1; 0.0.

72.45'

J.",\ .

Fi gu re 5-1

l ~2.. O.Dw ALUM SKIN

50 0 200 400 FTi __ e--I

SCALE

~ "s" TOwe:R

PLAN VIEW OF TYPICAL PANEL

I .. APEX i "c" TOWER

~t COWNt.EAC TRUSS

DECO 43-21 &30319 l

ELEVATION"B" TOWER

1175'

BOO'

1100

11300'

I

I1200' r

CROSS-PANELCATENARY

ELEVATI ~N

"An TOWER996.36'

I

--4-I

I

~ ... 11' i':"'700' ~ DOWNlEAO

• • 2002.35' _I: .. 2124.15' .. j . "

<t •A TOWER ~ B TOWER ~ • C TOWER

U1i..,.

2S0 soo 1000 SO 0 100 200!

_ HOIIZUNTJL SCALE - FrU VEIHICAL SCALE - FUr

I Figure 5-2 ELEVATION VIEW OF LONGITUDINAL PANEL CReSS SECTION - TOP HAT I I

I

DECO "." 03"19 BR I

ELEYATION+ '"c" TOWER1271. 7' I

I

---J.oo",. ~

CENTRO 10 ElEVA TI ON • 900'

t1>00'

I

t- E'LEYATION"B" TOWER1m'

I

i'00'

1200'

ELEVATION"A" TOWER99G.3G'

Itao' Ii. DOWN LEAD TRUSS

I. 2002.35' ... 2124.15' .. IG. ''e'' TOWER Ii. "c" TOWER"q: "f' TOWER

NOTE: FULL SCALE DIMENSiONS SHOWN.MODELED AT 1:100 SCALE.

U1I

U1

.,0 ~oo 1000 ~o 100 200

HO~IZONTAL SCALE· FEET VHT I CAL SCALE • FEET

Figure 5-3 ELEVATION VIEW OF LONGITUDINAL PANEL CROSS SECTIONAS MODELED - TOP HAT I

DECO 43-1 63U22 TH A

SWITCHHOUSING

SWITCHHOUS I NO

CUSHIHG LOCATION

I

III~-- UAHSYITTER ROOM WALLIIIII

L ~77A"-;,,"'v7::{<;:"V7;l~~~"T7';f::<>77{:r::tv7:~~1TT-;C"V7;<:vY7;<';v7";~77':"TT7-n~

rTOWER OPENING

t OF TOWER

III

IIII

-t--'--t-t---t-- {-- - ------- ---­III1IIII

STABLE POINT TIE iUS

1~:-----------208' (2.08') -+--------===:1.. 93' (0.93')-----..j.-- --+-----111' (1.15') I

o 5 10 18 20 2S__.M. 80 100

iSCILE

NOTE: MODEL DIMENSIOHS SHOWN IN PIRENTHESIS

Flaure 5-4 INITIAL TRANSMITTER/HELIX BUILDING

5-6

it was not known whether a single bushing could be 0 btained which could

carry the entire base current, but the advantages of the single-bushing

approach warranted its inclusion in the initial ITlodel. This approach

uses external bus work to cOITlbine the six downleads rather than the

internal bus work used in the PER design. Although this required three

insulated downlead pulloff structures on the roof, it resulted in a reduced

inductance with a correspondingly higher resonant frequency.

5.1.4 Downleads

An 8-wire fan downlead was selected to provide a sufficiently high

resonant frequency froITl the results obtained under the resonant frequency

study (Section 3). Figure 5-5 shows the details of the downlead arrange­

ITlent. The spacing of the top hat conductors, designed to equalize the

charge distribution, was preserved at the top of the fan with a tapering

to uniforITl spacing at the hinge point. At the hinge, the 4-wire cage bus

continues to the T/HB roof area.

5.2 Evaluation of Initial Configuration

Upon conclusion of the antenna selection study, the initial configu­

ration was evaluated on the ITlodel range. This configuration was sub­

jected to a series of ITleasureITlents to deterITline its performance charac­

teristic s. The mea surement program consisted of determining the basic

antenna parameters frOITl which performance under emergency and norITlal

operating conditions were derived. Detailed data is presented in Appen­

dix A.

5.2. 1 Five-Panel (EITlergency) Performance

Prior to the erection of the sixth panel, tests were made to estab­

Ii ~h the performance characteristics of the antenna in a sitnulated eITler­

gency situation with only five panels in operation. It was expected that

5-7

C 64.5'<775')- •• - TY~ -lIr--r-=- 62.9 '(7 56")--1IIr 58'r9'(71~~~;,~ [

I ""1 13.3' 1

~J __~~(159B"!) I~d$1 DOWN LEAD TRuSS

DETAIL "c"

o . :-z......!·C· TOWER ELEVATION 1271' 112.71-)

IlEttlfJ'21 &30WIItIPA

\ \ \\\ II iIII ~"'~.. .,~llilIlU",,- HINGE ·'INT TERMINATION

~7'SPACES~10.52'11116")7.2' 17/8")8.33' ( 1'1

A

INSULATOR AND GRADINGRING ASSEMBLY

3B'(4.56")

43'15.16")

466.6'(4.B' )

462.5'14.75')

-- 900' EL. ----

- 400.77'(4') - - ~ OOWNLEAO TRUSS

-700'(84')-

12' (3116") COPPER TUBE

T/HB

TOWER

-500'(60") - ---~I

_HINGE POINT"

-~f

186'(22.3")

-J

/:lOll

~ '0 100 ?OO

~~CAL[ rtET

NOTE' EQUiVALENT FULL-SCALE DIMENSIONS SHOWN WITH MODEL DIMENSIONS IN PARENTHESIS

Fl2urs 5-5 DOWNLEAD DETAILS

5-8

this would reduce the capacitance and, hence, the power raaiating

capability.

The basic full- scale parameters detenuined together with the

derived characteristics for performance at 15.5 kc with 1 megawatt

radiated power are presented in Table 5-1. Base impedance data over

the entire frequency range, taken at a point at the floor of the T /HB,

is presented in Figure 5-6.

TABLE 5,-1

Parameters

Effective Height (ho )

Static Capacitance (Ca )

Re sonant Frequency (fa)

Performance Characteristic s

5-Pancl

~~erK~~£z.

625 feet

O. 1412 fJ-f

33.05kc

6-PanclNormal

625 feet

O. 1633 IJ.f

32.18 kc

Unloaded Bandwidth (bwo )

Base Reactance (Xb)

Base Voltage (Vo)

Top Hat Voltage (Vt)

Base Current (10 )

Radiation Resistance (Ro )

32.7 cps 37.7 cps

-56.7 ohms -48.3 ohms

144 kv 124 kv

185 kv 161 kv

2559 arnperes 2559 arnperes

O. 153 ohms O. 153 ohrns

The reduction in capacitance from the 6-panel case may be

seen from the data for the 6-panel operation which is also presented

in Table 5-1. For 6-panel operation, the static capacitance is O.1633fJ-f.

The 5-panel situation would be expected to have more than 5/6 or 83.3

5-9

DEOD ~a-21 630~OI 1M C

-80 __ --~ _ I

- -:::~I--' -- ,.. - - - . - . I

t II/~-- ~i~-' , -- ' , ... ~. I-100 -~_____' _ I I

=-=--==1='=-=-'118.8 KCt':--:::- --. 33.oa J!C I

20m~fttOOIE1Oltl:ITrIfIDJ1TI1llUnmm+++H+ H-1:Hii-HI1 jill II :I!/I':'.~ I HI.ITrrrdt:, .1 ~l-R~H nlr11t 111!H,j::

1-,-- TEST 21 MEASURED AT FLOOR OF mEl +Ll';I;.rl:=r= TRANSMITTER/HELIX 8U Ilol NB .. hi! I 'I +,', J :1111 1:"~,,;i~~ FIVE PANEl OPERATION .I ;: II 1JJ'l' I:~1--+-- RESONANT FREQUENCY = 33.01 KC -1 lJ8 II, i ' Ij,

I j 'i I I !"I I '

~I---~I----~'E~:::j'j"±I--tt~[rrmltii~W~m~fflffiOOII~ll~i'!~ill~1-20

I-I I Ir+J-~'~I 'I' lill,11111I--- 1j1·H I,II ,I iL !II

~ _~o~:W=_-=t,=l=t---+_t.-i:1::' ,:=1:::.[=l=+=I=l:t--J..U,tt-+t!.tl=~I:I:t.tj I II III I'[iil!...-- . I-- - . ~i" I III! mCo> 1-----J1.-J..-+-+,__-t-~-_t- II= -- f- _. -- - -~ - ,

~ I-- 1= ~ __ =-=- _ ~ ,/'. _ ' _ ,,- I! II 'I... -60 - - - --., ,. I I ' I,: ~ I

~. ~. ;/v . . , I 1 II ~I I

1-+-.. 1-_+_-+-_-I-+~>"I---1-t-+-+-++-t-+.f-+-t++++f+-H+H++++1 f+I++H+WH+J H j--:. ~JlV -- - . - -.".. I I "I

403020FlEQU ENeY - IIC

-120 t:::t::'::=c-J:::-l=t:t~I~ :::1=l:::::~"Lt:tH~W::l::i:.L·== -.1..:..1.:1:.;--., -Ltl:t-- .tiJ.J:.i.iW='..l.tIJ..:'llliWi ll lllliJlII:ll.tJ1LliIlllllWllJli10

Figure 5-6 MEASURED BASE REACTANCE - 5-PANEL OPERATION

5 - 10

percent of the normal capacitance, since some fringing occurs into the

area occupied by the missing panel. The actual 5-panel value is 86.5

percent of the normal capacitance. Reducing the antenna capacitance

increases the top hat voltage (for equal radiated power) above the 161 kv

design value. Also, the reduction in unloaded bandwidth is apparent.

As shown by Table 5-1, the effective height is not affected by the removal

of a panel.

5.2. Z Six-Panel (Normal) Performance

Following the 5-panel tests, the final panel was installed and all

measurements repeated to establish the performance under a normal

operating situation.

Basic full-scale parameters and derived operating characteristics

for the 6-panel situation are shown in Table 5-1. Base-impedance data

over the operating frequency range is shown in Figure 5.7. referred to

the floor of the T /HB as before.

The resonant frequency shown in Table 5-1 does not include the

expected !eduction due to residual tuning/coupling inductance. For the

estimated 10 percent reduction factor for this effect, the maximum ex­

pected operating frequency is approximately 28.96 kc, slightly above the

28.5 kc upper operating frequency established during the antenna selection

study.

The 6-panel model data confirmed all design predictions for full­

power performance and established the capabilities of the proposed

radiator as a satisfactory approach. Although a wider margin in reso­

nant frequency and bandwidth might have been desirable, these two factors

are inversely related necessitating a rather cri.tical compromise in this

area.

5 -11

......c-

20

~§

0 l=t--

t--

t--~

DECO 43-21 63D401 JI D

-+ H -H+I II il-~!+l-I' lii!!l:!! ~j:]QTEST 22 MEASURED AT HOOR OF lIooEl I '" '"I,. I'J.~""TRANSMITTER/HElIX BUILDING lT1T 'II!:I. 11 ;::11 1l!";:;I,!:SIX PANEL OPERATION . I : i I iii I I il'ilii:lRESONANT FREQUENCY· 32.18 KC - I' Wiil: 111I!! ill l

l!! II Ii!... ··l'· II I I, I" I

~- 1- j , I ! ill !1 -! ~ ~, I

40

F1aure 5-7 MEASURED BASE REACTANCE - 6-PANEL OPERATION

5-12

5.2.3 Gradient Distribution

The distribution of gradient on the antenna conductors was deter··

mined from current distribution studies performed on the modeL Figure

5 - 8 shows the current distribution on the typical static panel under nor­

mal full-power operation (i. e., 1 megawatt radiated) at 15.5 kc as derived

from model data. Details of this technique appear in Section 2.2.4, amI

the theoretical analysis in Appendix B. A photographic study of corona

on the model under 60-cycle excitation appears in Appendix E.

Areas of maximum gradient can be determined from the data pre­

sented in Figure 5··8 for points along the conductors where the slope of

the current as a function of distance along the wire is greatest. The maxi­

mUln gradient occurs on the two innermost (Nos. 4 and 5) conductors just

beyond (outer half) the cross-panel catenary, reaching a maximum value

of 0.74 kv/mm, somewhat below the 0.8 kv/mm design limit. It should

be noted that the outer two conductors on each panel half (Nos. '1 and 2,

7 and 8) are enlarged to 1.·1/2 inch diameter in the region of the inter­

mediate towers. This enlargement, from the 1··inch diameter figure for

the bulk of the top hat, results in tolerable gradient levels which would

otherwise be excessive. For example, the 1-1/2 inch outer conductor

exhibits a lTIaxilTIum gradient of 0.62 kv/mm just beyond the cross-panel

catenary, while a i-inch diameter conductor in this area would operate at

a gradient of 0.94 kv/mm for 1 megawatt radiated at 15.5 kc. This

value exceeds the 0.8 kv/mm rnaximum acceptable value, thereby sup­

porting the requirement for the larger diameter conductor in this area.

The discontinuity in the current distribution along each top hat

conductor at the cross-panel catenary (as shown in Figure 5-8) results

from the diversion of the current from the conductors out along the cate­

nary. Since the catenary is of considerably larger diameter (2-3/16 inch)

5-13

~lJflfAC£ GRADIENT (ESl

K .!!. KWh",1ES ' II <to

50

40

[I'0

L0

'0

40

~

w

~ 30

~20

'0

;0 ~SS KVlMM '

,002~64M';S-;M7

WIRE 48.5

--- .-

1845'

lo.JI9 KV.... "U1.Jlo,o<'19 AAjP$.Orf]

46QQ'

WIRE! a 8

1095'I . , ,..

I1095'

. 1-'CONDUCTOR K\HotOIlUolETER Ui.I'""':"AM?

IN INCHES,

-,00 114 55

1.50 9' 68

1200'

20

10

,o

L

WlRE 287

2080'

Z ll~'

Flaure 5--8 GRADIENT

i,1

,,,

~ ON TOP HAT I PANELDISTRIBUTION

5-14

than the other conductors. it provides a greater area trorn which dis­

placem.ent current flows to ground. Because of its large dialueter,

gradients along its surface are even lower than on the rest of the top

hat. For this reason, a detailed gradient study of this cable was not

considered necessary.

Gradient data obtained for the 8-wire fan downleads is shown in

Figure 5-9. This data was obtained in the salUe lUanner as that ob­

tained on the top hat. Except at the lower elevations, the gradient on

the downlead conductors is lower than on the top hat. While lUeasure­

lUent accuracy in the lower portion of the fan is rather poor, some

relatively high gradient are<ls are inniC'<'lterl 11f'<lr thf' hingf' point. How­

ever, these are not expected to lead to corona problelUs since additionaJ

shielding will be provided at the hinge (in the forlU of corona rings)

which tends to reduce conductor gradients on the fan.

5.3 Qevelopment of Final Configurati_~~

5.3. 1 Revi~~~_Tr~~~~iJ:!..er /!.:!:~!?~_Bu.il<!.i~JL

Several changes lUade in the T /HB warranted m.oelel verification.

RequirelUents for ·increased equiplUent space resulted in a general

enlargelUent of the building.. The internal features of the tuning/coupling

portion of the building (as shown in Figure 5-10) were developed and

lUodeled for operation at 28.5 kc. Provisions were made in the model

for lUeasuring antenna characteristics through the appropriate circuitry,

as well as through a short vertical lead as in the previous tests. A

further provision was made to allow lUeasurements to be lUade directly

at the CUllll110n feed point below the entrance bushings.

5-15

-~-------~--

VERTICAL SCALE IN rEf To :;0 IOU I~U

2 jNO HORIZONTAL SCALE

DEC 0 43- 21 63040B JM A

NOTES:

I-NUMBEREO POINTS INDICATE GRADIENTFOR NORMAL OPERATION AT 15.5 KCWITH I MEGAWATT RADIATED. DERIVEDFROM MOOEL DATA

2- SHADING INDICATES GRADIENT INEXCESS Of 0.8 KVlMM CRITICALDESIGN VALUE

F1iure 5-9 GRADIENT DISTRIBUTION ON DOWNLEAD - STATIC CONDITION

5 -16

DECO ~3-1 63032~ TN I

-l

I I811 TeH I , : I

__ ~~O~ ---:----I---L ~ I :-TOWER OPEHIHOI

o I I CORRIDOR I I

l~ I FHEOF::

I SWITCH ROOMS I I

1,-,-;~-ry-"""""","'77*,,--/t--m7-;<,",777?<"<,,-?1=I,*-r,I7;'T:"":'V::ry-"':-VTT:<""'<'"""TT7'<C';v-;--r;,,,,,y--~

r

COPPER WALL ON t 8ElIEEH CORRIDORFACE Of SWITCH ROOMS

1

....--------------220. (2.2·)-~

{ Of TOWER

OOWNlEIO 'Ull-OFf STRUCTURE

'!. Of TOWER

II

--- 1

STABlE lOIHT TIE 8US

06101~2025----- 50 15 100

iSCALE

NOTE: MOOH OIMENSIOHS SHOWN IN PARENIHESIS

Flaure 5-10 REVISED TRANSMITTER/HELIX BUILDING

5 -17

Du~l EntT_~~-!?_':l_~l::.i:ng~

As part of the reyision of the 'r fHB dual entrance bushings

replaced the '5ingle bushing or iginally modeled. This change reflected

the need for higher current.·carrying capability and for higher relia­

bility than could be obtained with a single bushing. Along with this

('hange, n rearrangPTnpnt in t.hP. c1nwnlead bt.swork on the T/HD roof

was required. Figure 5-10 also shows the revised bus configuration

over the roof area. Some minor reductIon of series inductance was

expected as a result of the change .

.~~~~PaJ.?-_<::!..r:'.~r}.'?!E2~~~.~~'1'_~J2..~.~L.t!

F'or the enlarged T /HB with dual bnshings, the basic antenna

parameters deter mined at the floor of the buildmg through a simulated

10 ..·inch vertical bus to the common feed pomt were: effective height,

613 feet, static capaCItance, 0.1634 jJ.f· ar.d resonant frequency, 32.25 kc.

Aside from a very minor reductIOn in el1ectlve heIght and a similar in­

crease in resonant frequency, practically no change resulted in basic

antenna characterIstics.

Base reactance data rneasured at bot.h the floor terminal of the

model and the common point below the bushings is shown in Figure 5·-11.

The £1001' terminal measurements reflect the insertion of a small induct­

ance attributed to the connec ting lead. The normal measuring point

throughout the model study was at the T/lfH floor terminal. This point

was selected for convenience and also 101' repeatability because of a

somewhat better connector configuration. The rneasurements at the

common point near the bushings requued a short flexible lead whose

position was only approximately repeatable. However, [rom measure­

ments at both inputs the approximate effect of a short section of "bus"

5-18

DECO 43-21 630401 NIP A

D

...,.=c:>

...c..>

'"'..:­c..>­...""

10 20

FREOUENCY - KC

30 40

FIKurB 5-11 MEASURED BASE REACTANCE AT TWO REFERENCE POI~TS

5-19

was determined. Since the residual inductance in the tuning/coupling

circuitry at the high end of the frequency range is a determining factor

in the critical area of maXImum operating frequency, it is necessary

to consider all reactance data referred to the appropIlate terminals.

Effect ~~~J_~oupli~.!L~i.:t:..cuitrL~~.!Ze~0!1~_n~~,

The approximate configuration of the tuning/ coupling component

arrangement and appropriate values for the upper end of the frequency

range were modeled as shown in Figures 5 12 and 5-13. Figure

5-14 showl; the nleasured input reactanc.e through the tuning/coupling

circuitry in the frequency range near resonance. The maximum oper,·

ating or self-resonant frequency is seen to be Z.Y,6 kc. This value i::l

about 4 percent above the minimum acceptable value 0,28.5 kc) pre­

viously established.

5.3. 2 .!3:~~2.~~~_,!:~,l2J::1:a~_,?~~'p'~

A structural analysis of stresses m the top hat. conductors unlIeI'

conditions of maximum wind loading showed that the proposed Top Hat I

design did not have acceptable sa{ety .. lactor margms. The ultimate

yield of the ACSR cables was degraded by t.he alummum outer layer to

such a point that then use was precluded. Therefore, a new top hat

design (Top Hat!i) utilizing only alummum-clad conductors was devel­

oped to maintain acceptable structural safety. factor margins during

periods of maximum wmd loadIng.

Jncre~~!opHat ~~~

Top Hat II, composed entirely of aluminum-clad steel conductors

has greater sag and, for the ::larne tower heIghts, a lower average physi­

cal height than Top Hat 'I. SpeClfIcally Top Hat:.! (as shown in Figure

5--15) has an average height of 891 feet as c.ompared to 900 feet for Top

5- Z 0

,-

10 0 10___ - :aSCALE- FEET

DECO 43-21 630405 DP Z

Figure 5-12 PICTORIAL SCHEMATI C OF MODELED TUNING/COUPLING CIRCUITRYAT 28. 5 KC

5-21

lJlI[\J

[\J

Figura 5-13 PHOTOGRAPH OF MODELED TUNING/CCUPLING CIRCUITRYVIEWED FROM BENEATH T/HB

r-------------~------------,DECO 43-21 630401 11 a

I I ! j I! II I II II

I IIi I II I I I Ii-20 I)' II I. Ii Iii

I I \I !'III 'I! II!! II, I Ii lid' I-Ii, I I I - I ! 11 II II i j i! iii", I! i1111

-100 I

--

I-120

10

15.8 ltCl

I20

FIEQU my - KC30 40

Fliure 5-14 MEASURED BASE REACTANCE INCLUDING TUNING/COUPLING CIRCUITRY

5-23

~2002'35'

'A- TOWER

250 a 'DO 1000!

T"'"DECO 4-3-21 630319 G

..r

ELEVHION = 1271'--- ~--""l-

~,,~,Jt DOINLEAD TRUSS

"".15' '.• C· TOWER

100 206

CENTROID ELEVATION' 891

-!:;- - - -

10laO

800'

"B- TOWER

~2DO'

ELEVATION'8: TOWER = 1175'

• . 1100",

CROSS-PANELCA TEHARY*" 110 ..

I ,

U1IC'"

"""

HOR I ZONUl SCALE - FEET 'ERT ICAL SCllE - FEET

Figure 5-15 ELEVATION VIEW OF LONGITUDINAL PANEL CROSS SECTiONTOP HAT II

Hat 1. To determine the extent of degradation resulting from this loss

in average height, the Top Hat II configuration was modeled with the

two-point sag approximation shown in Figure 5-16. This required an

entirely new set of model top hat panels since the revised design em­

ploys longer conductors and increased sags.

Six Panel Performa_r:..::...~JIopHat II)

The reduction in average physical height of the top loading was

expected to produce a corresponding reduction in effective height.

Basic full-scale antenna parameters measured at the normal T /HB

floor were determined from the model (Test 26, Appendix A). These

paran.eters were: effective height, 610 feel; static capacitance, 0.1642 fJ.f;

and resonant frequency, 32.45 kc.

Comparing the effective height of Top Hat II (Test 26) to that of

Top Hat I (Test 25) shows a reduction of 13 feet, i. e .• somewhat greater

than but comparable to. the 9 foot reduction in average physical height.

The indication from this comparison is that with the increased sag, the

average height should be elevated at least to the previous 900 feet to

achieve the same value of effective height. Since the descrepancy of

4 feet between the variation of effective height and average physical

height is well within the ±2 percent predicted test accuracy, no further

compensation is justified. For small changes in the "B" tower elevations,

it can be shown that the average height changes by one-half the increment

of change. On this basis, a recommendation was made to elevate the "B"

towers 20 feet to compensate for increase sag.

Three tests were rlln with the Top Hat n in position. Test 26

relates to the basic antenna viewed through the normal T /HB terminals.

Test 27 relates to data derived from measurements made at the common

5-25

DECO 43-21 63D319 HR

__ 1 __

ELEVATIONt"c" TOWER1271'

IELEYA TI ON"e" TOWER

1175 '

11 DO'

7DO'

eao'

1300'

1200'

CROSS-PINELCATENARY

II

I I

~.00.77' ~

Cl. DOWN LE1D TRU SS

I""' 2002.35' -I 2124.15' ~Ci •A~ TO rER Cl. "e" TOWE R (rC" TO m

NOTE: FULL SCALE 0IMENS I ONS SHOWN.MODELED AT 1:100 SCALE.

U"1IN0'

210 0 eoo 1000!

eo 100 200

MOR IzeITAl SCAlf - ~Ef1 VERTICAL SCALE - FEET

FliUll 5-16 ELEVATION VIEW OF LONGITUDINAL PANEL CROSS SECTIONAS MODELE~ - TOP HAT II

lead point near the entrance bushings (i. e., excluding the roof-to-floor

bus inductance). Test 28 defines the ITlaximum operating frequency to

be 29.43 kc including the effect of the tuning/coupling circuitry (see

Appendix A).

5.3. 3 .I3:~_~~~To~_~ Hei~!.J._~~_

"B" Tower Com~~Esati~~

To restore antenna performance (particularly effective height)

to values achieved prior to the increased sag of Top Hat II, the elevation

of the intermediate "B" towers was increased by 20 feet to 1195 feet.

This brought the average top hat elevation to approximately 901 feet,

or 1 foot above the Top Hat I value. Although the top hat sags and con­

ductor lengths remained virtually unchanged for this small variation

in the "B" tower elevations, the revised configuration is referred to as

Top Hat HI for reference. Figure 5- 1 7 shows a longitudinal panel cross

section of Top Hat LG in elevation. The modeled version of this design

is shown in Figure 5-18. For modeling purposes, the top hat p:mels

used were identical to those of Top Hat H.

F'or the revised top hat with the recommended 20-foot "D" tuwer

compensation, the basic antenna parameters measured at the T /HE floor

were: effective height, 629 feet; static capacitance, 0.1633 l.lf; and reso­

nantfrequency, 32.45 kc.

Comparing these values with those obtained with Top Hat I (which

involved only one bushing), it is apparent that the compensation for in­

creased sag was sufficient to restore, or slightly increase, the effective

height while the static capacitance remained the saIne. SaIne minor re­

duction of series inductance through two bushings instead of one appar­

ently accounts for a slight increase in the resonant frequency from 32.18

kc to the 32.45 kc value shown above.

5-27

DECO 43 21 630403 DPA

HEUTIONi"C· TOWER1272' ,

~ m.l1'r-Ci DOWNLEAD TRUSS

t 1.300'

I

---l1200'

I

ELEVATION"8" TOWER

1195'

CROSS-PANELCATENARY

ELEVATION"A" TOWER996 .•0'

I ~100'~'------2002.35' .1 ~ 212 •. 15' ..I

G. "f'TOWER Ci "ihTONER <t "c" TOWER

U"1I

N00

250 soo 10 100 200

MOR IIONUL SCALE - FEET Vt~TlCAL SCAlf - FtET

Figure 5-17 ELEVATION VIEW OF LONGITUDINAL PANEL CROSS SECTIONTOP HAT ill

DECO 43-21 630403 DP~

ElEYATIO! t,'C" TOWE! I1211.7'

IEl EY AT ION"B" TOWER

1195'

1100'

11300'

I

i-III

1200'

CROSS-PANEL --,1,./1 \CATEHARY

ELEVATION~ "I" TOWER1\ 996.3,'

KOTE: FULL SCAlE DIMENSIONS SHOWN.MOOELEO AT 1: 1DO SCALE.

V1I

N-.0

200100505002:;n

I

: • _>CD..,5' t10< ----., 40D 11' I., "" """ _ I - r-I ' ," "''''"' ' DO'''''' ""IS

Q B TOWER ·1f'c" TOWER

nOR IZOHUl SCAlE - FEET VERlI Cll SCALE • FEET

Figure 5-18 ELEVATION VIEW OF LONGITUDINAL PANEL CROSS SECTIONAS MODELED - TOP HAT III

Figure 5 -19 shows the input reac tance measured at both the T/HB

terminal (Test 31) and at the common point below the dual bushings (Test

30). Comparing the two sets of data shows that the difference can be

described by a series inductance of approximately 14.3 fJ-h \full scale

value). Using this value, it is possible to refer all reactance data from

the floor terminal to the common point.

The maximum operating frequency was determined for the Top

Hat III configuration in Test 2.9. With the modeled tuning/coupling cir­

cuitry at the upper portion of the frequency range, the system resonant

frequency was reduced to 2.9.45 kc, only 0.5 percent below the value

achieved with the initial configuration (Top Hat I).

5.3.4 Wind Distortion Study

To establish the performance reliability of the antenna to perform

under extreme wind distortion, a model study was made for the distorted

configuration. For design purposes a maximum wind of 130 mph velocity

(at 3D-foot elevation) was established. Com.putations were carried out

for various wind directions with respect to a typical panel, and con­

ductor positions were established. The particular wind orientation

chosen for the model study was one in which two panels were subjectecl

to a direct cross wind as l'ihown in Figure 5·-20. Although the choice of

this case was aribtrary, it was felt that it represented an extreme dis­

tortion and, as such, was likely to indicate the extreme degradation of

electrical characteristics.

FrOlTl the computed positions of the top hat conductors {Top Hat

III), largc··scale plan and elevation drawings were marlp of pac:h c:on­

ductor span. On these drawings a two-point approximation was con­

structed to simulate the distorted condition. Each half panel was inter­

sected by two "distortion planes", the intersection of each individual

5-30

DECO 43-21 630401 NlP 9

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I I I I II! jl I I i I ItIl i : I III I! iii il·lll. '1:. iii:! i I~..;~~::-;Ij :1' I I I i It-! 11 i I jl ilj~, I 1!!I'IIIJ. :.or""I - 1- . I Iii",'" !;I~~ :, .

1 I, ! I! III Ii I' j I I I! I! I ! TEST 31 tJ~m! ii!;:!~,:c-!-. I ,I 'i ,i I 1 I I i I Ii,. T~~!: iii I : I:::;::::

1

1:'1 I:,; 11!1 1 1 ~.!'!' !I'I;I"III:;'I+'II II ' I " " ! II i I, II.p'!!·I I I y.l lll~lj~I~~I;

_20 I ' ! I ", 1! TEST 3D " 1 : ,. iI' , .•

00 -U: I !! I II i III! I '~~I! I 1III,.!i! :!: :::::.:1 '.' ..·..::r ..·:.:~ I I 1 I ~ Ii II IIiI jil, II Iii il il,:!' : '1"lli!l:::!.:. - 40 f-+-+-+'.-,il-+++-+-~I+-+-++:',fqo<-l.;I-~f++++l-++i+++1++++++~-+++:+!I M'H-''Hoi':+;''r+t'~';-4-;:'ri-I:

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1 II :1 I Iii IIIII:,:I:;!: iii;!:;;! il:;:I:11-80 I- - IlEASURED AT FLOOR OF 1l0DEl ~

~If t I i 6~m~~'m:m~~X BUILDING !!,-1 -+-t-+-f---jf--+---j---+-+'+++1 RESONANT FREQUENCY = 32.46 KC -IJi-

I - -----IlEASURED AT TtE BAR BETWEEN ,1!1_----- BUSHINGS IN 1l0DEL TRANSMITTER/ ill

- 100 r-+-+-+-+-+-t-+++++-t-ti HEll X BUI LDING T.. - -- - 6-P1NEL DPERATION

... __ .i RESONANT FREQUENCY = 33. Be KC I

!~ -i-rlTflllli 1111111111111," 1111 iiI11II1 IL-I..-.l...-.L.....l.....L-L..L..L..L...J..-L-l-......L..L.L.W....l.

10 20

FREQUENCY - KC

30 40

FlgurB 5-19 ~EASURED BASE REACTANCE AT TWO REFERENCE POINTS

5-31

,---------- STATIC LOADWI~D LOAD

1000 2000 3000

i

DECO 43 21 630320 C

SCALE - FEET

Figure 5-20 PLAN VIEW OF ANTENNA UNDER MAXIMUM WIND DiSTORTION

5-32

conductor with the distortion planes being derived froITl the drawings.

Poles were then rigged on both sides of each panel in the distortion

planes to support nylon lines constraining the ITlodel conductors in

their proper positions.

Figure s 5 - 21, 5 - 22, and 5 -23 show the three wind attack angles.

The plan pusitiull anu elevation oJ edch conlrol point deterITlines the top

hat shape.

As the top hat is lifted and displaced, the associated downleads

are similarly distorted. Figures 5-24, t;_25, and 5-26 show the various

downlead positions used on the ITlodel to siITlulate ITlaximuITl wind (130

mph). It was observed that of' the three representative downleaus, only

the No. 2 fan approaches the center tower guys. Consequently, it was

expected and confirmed by measurement that the critical area of corona

formation occurred at the point where the No. 2 fan is displaced into

close proxin1.ity with the top two guy levels (See Figure E-3 , Appendix E).

Detailed structural analysis revealed a similar deflection of the offending

guys in the direction of the wind which tended to alleviate the probleITl.

However, it was found necessary to study the effect of providing addi­

tional fan-guy separation appropriate to lower wind velocities.

Six-Panel Performance

After all positioning poles were erected for the distortion rigging,

but before the ITlodel was actually distorted, the basic antenna properties

were ITleasured to establish the effect, if any, of the 36 holes and nurner··

ous nylon lines. Although considerable care was taken in preparing the

wooden poles by drying and shellacing, it was expected that SOllle llliuol'

effect would probably result. In general, the effect can be explained by

5-33

{I.S () 2.0 4,0

~SCALE-FEET

---DOWNLEAD TRUSS

/

(!)<>~

I

/

·c· TOWER

~,,",~"'--=t--_~'"1--~~--f::-_---J!:~--~f!l18L-<1 Ii."8" TOWER

MODEL ELEVATIONS IN FEET

POINT ELEV~ION POI!!! ELEVATION

I 9.69 23 10.29

2 9.45 24 ILII

3 9.51 25 11.304 9.39 26 10.56

5 9.19 27 10.27

6 9.32 28 9.90

7 9.61 29 9.14

8 9.67 30 8.93

9 9.90 31 9.19

10 10.44 32 9.63

\I 10.33 33 10.03

12 9.81 34 9.71

13 9.22 35 9.62

14 8.98 36 9.27

15 9.37 37 9.17

16 9.76 38 9.27

17 9.77 39 9.83

18 10.82 40 9.95

19 9.57 41 10,17

20 9.61 42

21 9.14 43 10.0622 9.47

NOTE' DIMENSIONS S~OWNAPPLY TO SCALE MODEL.

t "A" TOWER

Figure 5-21 PLAN VIEW OF PANEL 1 UNDER MAXIMUM WIND DISTORTIDN

5-34

HC' U-JI IilUU ~

MODEL ELEVATIONS IN FEET

POINT ELEVATiON POINT ELEVATiONf 'C'TOWER

I 9.72 23 10.732 9.52 24 11.~4

3 9.45 25 11.47

4 9.~4 26 10.585 9.~9 27 10.91 DOWNLEAO TRUSS6 9.60 28 10.55

7 9.85 29 10.048 9.97 ~O 9.759 9.99 31 9.7410 10.56 ~2 9.99II 10.50 33 10.0812 10.18 34 10.18

I~ 9.71 35 10.15

14 5.~5 36 10.11

15 9.35 37 10.1516 9.68 38 10.3417 9.82 39 10.59

18 10.60 40 10.7719 10.35 41 10.8020 9.74 42

21 9.59 43 10.5022 10.03-

~ - 20 1918

~ "8"TOWER

NOTE: DIMENSIONS SHOWN APPLY TO SCALE MODEL

t "A" TOWER

Figure 6-22 PLAN VIEW OF PANEL 2 UNDER MAXIMUM WIND DiSTORTION

5-35

neG U-lI 6JOUJ D

~ "c" TOWER

MODEL ELEVATIONS IN FEET

NOTE: DIMENSiONS SHOWN APPLYTO SCALE MODEL

POINT ELEVATION

10.66

POINT ELEVATION

9.32 23 11.419. 23c--1f-~24':-+-:-:II'-:-:.10

9.15 25 II. 28

8. 7::,0C--1~_c2;:;;6;--r-:1c:;0'-,:64~---j8.51 27 10.56

-c8.c::"4:<-8_11-- 28 10.088.89 29 9.64

9 .~25=----11-----=-30 --+ --.=9.:.:.5:.:0'---19.34 31 9.76

9.99 32 9.54

9.86 _n_----"3:3.-+----"9,,,.1.=.89.27 34 9.14

8.53 35 9.53

8.62 36 10.00

9.02 37 9.839.62 38"9:90"

9.81 39 "1O:T7

10.87 40 10.3910.69 41 10.46

9.97 429.61 43

9.79

I

2

3

45

67

8

9

10II

12

13

141516

1718

19202122

l'A Il TOWER

FlaUfa 5-23 PLAN VIEW OF PANEL 3 UNDER MAXIMUM WIND DISTORTION

5-36

DECO 43-21 630405 MP A

MOTE: WINO DEFLECTION Of TOWEROUYS NOT SHOWN

1 iSTATI C PANEL Ii.

Ii. "c" TOWER

OOWNLEAO TRUSS

HINDE POINT

ELEVATION 99" -- -."..-....,..,.""....-

t OF S-WIRE FAN --- -l

"

~ MODELOEFLECTINO

PO IHTS

SCALE - fEET T/HB

4-WIRE em~

100 200__ i

DIMENSIONS ARE fOR fU,L-SCALE ANTENNA.MOOELEO AT 1: 100 SCALE

Figure 5-24 PANEL 1 FAN DOWNLEAD UNDER MAXIMUM WIND DISTORTION

5 -37

DECO 43-21 630405 NP B

NOTE: WIND DF.FLECTION OF TOWEROUY S NO T SNOWN

WIND

STATIC PUEL

- SEE TABLE

DIMENSIONS ARE FOR FUll-SCALE ANTENNA.MODELED AT 1: IDD SCALE. ~ U( TOWER

MAX. 130 MPN 20 FT

TlNB

WIND VELOCiTY CRITICAL OUY-FANSEPARATION

£ OF 8-WIRE fAN

OOWHLEAD TRUSS

Hi ri

4-W1 RE CADE

45 FT

iU !iFii

100 0 200

.- iSCALE - FEET

110 MPN

Figure 5-25 PANEL 2 FAN DOWNLEAD UNDER WIND DISTORTION

5 -38

DECO 13-21 630405 NP C

NDTE: WIND DEFLECTION DF TOWERBUYS NOT SNOWN

Il. .. C· TDWER

~ OF 8-WIRE FAN

DOWN LEAD TRUSS

1\o""'~~-ElEVATION 1070'

TINS

I DO 0 2DO

~ ] 4-WIRE cm"SCAlE - fEET

DINENSIONS IRE FOR FULL-SCAlE ANTENNA.MODElED AT I: 1DO SCAlE,

Fiaure 5-26 PANEL 3 FAN DOWNLEAD UNDER MAXIMUM WIND DISTORTION

5 -39

considering the poles and rigging as a path for excess polarization

current2 , that is, vertical displacenlent current in excess of the

current which would flow in the absence of the dielectric rigging. If

the rigging effect increases the relative dielectric constant K for the

region of the antenna, the capacity C s can be expected to increase

and the effective height to decrease according to the following rela-

tions:

Dielectric Air _~2~-±-~i~gin.!i------

• Effective Height h o h o /K

• Static Capacitance C s KCs

• Dielectric Constant 1 K

COITlparing Tests 35 (Air) and 36 (Air + Rigging) for the unclis­

torted top hat (III) yields the following full scale values:

Air .A i_r_~_Ri g_gin~ Perc~~t Change

• EfJective Height 628ft. 619 n. -1. H

CI Static Capacitance 0.1637 JJ.f 0.1640 JJ.f to. 18

• Resonant Frequency 32.28 kc 32.38kc 0

Although the trend of effective height and capacitance change are

all expected, the relallo!l oJ these paralnetel's tu an effective dielectric

ccnstant K is not exact. Apparently the distribution of poles and rigging

near the top hat is not sufficiently unifornl to pernlit the sinlple relations

described above to be applied. Since, however, the total change in

a S. A. Shelkunoff andH. T. Friis, Antennas, Theory and Practice.John Wiley and Sons (1952). (Sec S~~ti~-;'To--:-14~Magneti"calG--and

Dielectl'ically Loaded Antennas. )

5-40

effective height is less than 2 percent (the predicted tolerance on this

parameter) and the ca.pacitance change even less, it appears that the

effect of the distortion rigging was practically negligible.

For the top hat (6 panels) under maximum wind distortion, the

following data was obtained at the normal T IRB floor terminal (Test 36):

effective height, 684 feet; static capacitance, 0.15'15 ILf; and resonant

frequency, 30.68 kc.

Base reactance data for the wind-distorted configuration is

plotted in Figure 5-27. Physically, the horizontal wind loading has thc

effect of rotating the plane of each sagging top hat span toward the hori­

zontal, the degree of rotation depending on the angle between the wind

and the span. This has the effect of raising the average top hat eleva­

tion, thus increasing the effective height, and reducing the capacitance.

If the antenna could be represented by a single (top loading) capacitance

and a single thin, conducting downlead, free of the perturbing influence

of grounded towers and long, relatively low, horizontal runs of cage

conductors, then the increase in effective height due to an increase in

the average top hat height would be approximately the same as the de­

crease in capacitance. However, for an antenna with a considerable

near-base capacitance and luany parasitic conducting structures, the

two effects are not comparable. In particular, elevating the horizontal

downlead bus -work (connecting the hinge points and the pulloff points on

the TlHB) greatly reduces the near-base capacitance. This has the

effect of raising the apparent effective height (i. e., reducing the loading

effect of the near-base capacitance) and adding to the increase in the

average top-loading which yields an exaggerated (positive) change in

effective height compared to the (negative) change in static capacitance.

(See Appendix D. )

5-41

-

DECO 43- 21 630401 JII A

403020FREQUENCY - Kc

,III .1+.V ,+ill "IJj '111 ;!11·':,, 1IIII T~

TEST 3& TOP HAT.m UNDER lUX I MUM I I-I ~i! --Jj- ' "1 1 I I":; ,~

f- o ~ I !I" I 't:t= Ij'~1 Iii""'"11110 DISTORTION 'T - - ~ I! , , • I' . !::" ... ,

:=~ MEASURED AT FLOOR OF MODEL 1_:,' _- " I .I' I I ~. i ' , , ' , '- " IJ).n!,' ,1'",:,;,- TRANSMITTER/HELIX BUILDINB I-I I, jll'l!irl;p,,-f-- RESONANT FREQUENCY .. 30. &8 KC l II!, Ii': !I'%f-f- I " I! I j. I, ,.,

: I I ~ I tI !1: ! ~ I . !

c--f-,I

'I!IIW !ij!!Hii'--f- -- - - , 1 - . !i!::II:i !lllj::.!- . 1 . ; I ~ I ~ : I ! l ' i I ~ , II ~

.1',1" •. "'1'11 1,\~~;,il'~ "il~~~d

f-- - - - :;IJ:i:l: ;:;;:1;11- f- I-

""I'! I ii, ;, :1;,rrtl

f- f- d 11 1"11 II' I""II' "I I iii ,·1,)~, ,ii iii Ii , Ii (, I

f-'-- .- ~~II ililllllill!:111!!1

- - 1- -I- e-- ~ Ial! :I! ii !III; II I- ---I-~ /" - - -

I~i II! IIi' ilillm!---- - -- - - -

,-1- - -f- ~- - --

'!I,liiilll,I':li l- l- I- I-f- - -- -

1=1 !Iil''II' I

,'II- --- - - -- - .

i I! I~I- - - -- I----- I' -

--V!L- - -- - II.- l- . -_. - ,I' I- -- - - -

1- -;/f- -- -

~- -, ---- --. - . - - -

.II I I I1- _. - - -,_.-1- - - -

--- -f- -- - - - --- I

- - 1- -I--- ----- - - - --- .

~II-I

If- - --- . -- - - .

1.1f- .-f- I--- -- -- - -- -- -

f- ---f--I-f- --.--f- -- --- .

f-- - I-I--- -- - -- -- - - -1- -f:~a.~s II--1- --. -- - -.

f-- --'- -- --

la.a KC ~- - - . - -

I--- Kef--

tl~1~~ :lllmlil IIrf--f- -

-12010

-100

-so

20

-20

o

...==C> -40

I..."'"a:oC..."'"oC...: -&0::..

Figure 5-27 MEASURED BASE REACTANCE FOR TOP HAT IIIUNDER MAXIMUM WIND DiSTORTION

5-42

Comparing the rneasured antenna cnaracteristics under static

and :maxhnu:m wind conditions yields the following full- scale data:

e Effective Height

• Static Capacitance

• Resonant Frequency

Test 35StaticLoading

619 feet

0.1640 flf

32.28 kc

Test 36Max. WindLoading

684 feet

O. 1575 flf

30.68 kc

PercentChange

+10.5

-3.96

-4.94

Since all the downlead trusses are lifted by the wind, the down­

lead bundle acquires a so:mewhat longer and thinner shape. This, 1.0-

gether with the increase in average top hat elevation, accounts for the

associated increase in inductance and reduction in resonant frequency.

Under the condition of :maxi:mum wind distortion, the simulated

tuning/coupling circuitry appropriate to operation at the upper end of

the frequency range was inserted (Test 39). and input. reactance was

:measured to deter:mine resonance. For this arrangement resonance

occurs at a scaled frequency of 28.25 kc, some 0.25 kc below the 28.50

kc figure specified. However, since the predicted frequency of occur­

rence of 130 mph winds is approximately once in 50 years, the situation

was considered tolerable.

Gradient Distribution

Current distribution measurements were perfol'med at a scale

frequency corresponding to 15.6 kc (i. e., 1560 kc) using the shielded

oscillator probe in a manner similar to tbat outlined in Section 2.2.4

for the case of Top Hat I under static loading. From the current dis-

tribution, the electric field gradient is determined from the change in

current per unit area of top hat conductor (See Appendix B).

5-43

Under conditions of maximum wind loading, the antenna conductor s

are displaced from their static or dead-load position, changing the various

spacings between conductors and between conductors and ground. This

distortion changes the current distribution, increasing the gradient in

some areas. C::-itical areas of increased gradient were expected at points

where top hat and downleads were blown towards grolmded towers and guys.

Figures 5-28 through 5 -33 show the distribution of gradient on

the three wind-distorted top-hat panels appropriate to the maximum wind

orientation chosen for study.

Although the expected increase in maximum gradient on the top

hat was observed, the critical area of intere~t wa~ U11 the No.2 panel

downlead fan. This parHcular downlead is displaced toward a guy plane

[or the chosen wind. Some advantage is gained by vir'tue of a simjlar de-

flection of the guys, but not sufficiently to preclude the possibility of a

liITlited area of corona formation. The other downleads (Nos. 1 and 3)

are not deflected to positions near towers or guys, 50 that only the No.2

fans are critical.

To provide detailed information on the No. C, fans, three wind

velocities were studied which would indicate several situations expected

during periods of storm activity. Figures 5·34, 5··35, and 5·-36 show the

critical downlead under 130, 110, and 90 mph winds, respectively. Under

these conditions the following relations were obtained:

Maximum PowerNo. Z Down·- Gradient Radi.ated Frequency

Gust Velocity lead-Guy (1 Mw (0.8 Kv/mm of Occur-at 30 feet ~~paration Radiated) Gradi.entj renee.------- ------130 l'nph 20 feet 1,3 kv /min 380 kw 1 in 50 yrs.

110 lnph 45 feet 0.9 kv /mrn 480 kw 1 in 15 yrs.

90 mph 70 feet 0.8 kv /mm 1000 kw 1 in 6 yrs.

5-44

60

'0

60

40

30

20WIRE 4

10

oJ---------~~------~-o

OOWNLEADTRUSS

'0

Deco: 43·;::' 630411 NJP B

Sll~FACE GRADIENT IEsl

E$ • K~ :-; i(V/'-Ul

CONDucTORIK.DIAMETER ISi'.:1!!IN INCHES .MY-AMP_

tOO I~.~~ .01.50 9.68 UI

I W

~jr30~

~ ~~ ~

~.,.,~ 20

6 -"'-".II/If WIRE 4

--400'

~~ 10

~--------------r------ -~--- ~ 0o

DOWNLEAOTRUSS

'0

40

20

.0

W«

30~

20

10

o·o

OOWNLEAOTRUSS

50

WIRE 3

"800'

WIRE 310

oo

DOWHLEADTRUSS

40

30

20

0----­o

OOWNLEADT~USS

[o

DUT£RAPEX

50

20

10

oo

OOWNlEADTRUSS

CONQUCTOR LENGTH MEASURED tnOM !:"J'l'!~I~EAO TRUSS TOWARDS

•CATENARY

40

30

20

10

oo

OUTERAP[X

CONDUCTOR LENGTH MEASURED FROM OUHH APEX TOWAHOS (ArEHART.....-GRADIENT DISTRIBUTION UND~R MAXIMUM WIND ON PANEL

(WIRES 1-4)

5-45

DECO 43· ~I 630411 'W' A

'"

60

'0

40

SURFA.CE GRADIENT IE,I

E•• ~* KV/MM

, "COP(OUCTOR KV.M

D{hi1flHl~ MM7"AAlP100 14.55

1.50 9.69

----------+0o

OUTERAPEX

WIRE 8I"; CABL.E

'"

20

oi-o~~~~~~~~-~~~~~~.-J

OO"I~L("A.OTRUSS

60

40

30

20

40 WIRE e~_.------

'0

.w~ 30

~

60 >60

'"WIRE e

60

20 20

'0· '0

oo

OOWNLEAOTRUSS

--10,:!._,~~nAPEX

60·

60

WiRE ~ 60

60

20

'0

20

oo

OOWNLEADTRUSS

CO'lDUCTOR LENGHi MEASURED FROM DOWNLEA.O TRUSS TOWARDS CATENARy

• I~O

SCAtt - rHT

"----..,- r.J.-__

---~400'- ---~__

~----------==40

oOUT£RAPEX

cmlWCTOR LEflGTH ME"'SUREO fROM OUTER APEX TOWAROS CATENARY

~

Figure 5-29 ORADIENT DISTRIBUTION UNDER MAXIMUM WIND ON PANEL(WIRES 5-8)

5-46

~ -----DECO 4!. 21 630411 NJP C

WIRE 4 WIRE 4

SURfACE GRADIENT (E,I

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NOTES:

1- NUMBERED POINTS INDICATE GRADIENT FORNORMAL OPERATION AT 15.5 kC WITH IMEGAWATT RADIATED. DERIVED FROM MODELDATA.

2-SHADING INDICATES GRADIENT IN EXCESS OFO.B K\lIMM CRITICAL DESIGN VALUE.

Figure 5-34

VERTICAL SCALE IN FEETo 50 100 150c:= ~

NO HORIZONTAL SCALE

GRADIENT DISTRIBUTION ON CRITICAL (No.2 FAN) DOWNLEADUNDER 130 MPH WIND

5-51

DECO 43-21 630407 DP 8

EL 1080'

NOTES

1- NUMBEREQ POINTS INDICATE GRADIENT FORNORMAL OPERATION AT 15.5 KC WITU I MEGAWATTRADIATED. DERIVED FROM MODEL DATA

2- SHADING INDICATES GRADIENT IN EXCESS OFDB KV/MM CRITICAL DESIGN VALUE

VERTIDAl SCALE IN FEETo 50 100!

150a

NO HORIZONTAL seAL"!!

Figura 5-35 GRADIENT DiSTRIBUTION ON CRITICAL (No.2 FAN) DOWNLEADUNDER 110 MPH WIND

5-52

r.25

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2- SHADING INDICATES GRADIENT IN EXCESS OF0.8 KVlMM CRITICAL DESIGN VALUE

VERTICAL SCALE IN FEETo 50 100 150E :a

NO HORIZONTAL SCALE

Figure 5-36 BHOIEn DiSTRIBUTION ON CRITICAL (NO.2 FAN) DOWNLEADUNDER 90 MPH WIND

5-53

---'Chic. l'(,P01'~ prC'scnt" the results of th(~ i1ntC'nna. nlodel study which

-.vas C:~l'~led out for the dcvclopnlent of t.he design of the VLF PAC antenna.

Beginning with an evaluation of tlw initial coniiguration (Section 5. 1) this

study includes the results of a continuous nlodd progranl involving

detailed structural revisions which occurred as part of the refined design.

These revisions included changes in top hat shape, intermediate tower

elevations, entrance bushings and Transmitter/Helix Building. In gen-

~-----~ ' .. e:tal, ther"eilects of such revisions were reflected by relatively minor

changes in electrical performance as derived f~~m model measurements.\ \

Consequently, the mcasurenlent of some aspects"of performance which

were not considered of prima ry importanc e or '.vere not expected to

change appreciably were not repeated for the final revisions.

For comparison, Tai>~e 6-1 summarizes both the predicted full-

scale basic antenna pi\rameters and the derived operating characteristics

relating to full-power (1 megawatt radiated) operation at the design

frequency (15.5 kc). This data is given for (a) normal (6 panel, no wind)

operation, (b) emergency (5 panel, no wind) operation, and (c) for the

condition r 6 panels and maximum winn. (1.30 mph) distortion. The

normal and wind-distorted data w"rc obtained from the final model

with all pertinent revisions included. However, the emergency con­

dition was evaluated only on the initial configuration. Since no major

changes w~re determined in the performance for the normal condition

(compare, for example, the results of Tests 22 and 34) it was consid­

ered unnecessary to repeat the en1ergency condit~on measurements.

The base reactance values shown in Table \-1 include all

corrections and i1re rcfcrrc:J 10 the bushll'!; t'r:~l,tn'-" on Ihp antenna.\

Figure 6-1 is a plot of the corrected input reactance over the entire

• 6-1

TABLE 6-1

Sumn"lary of Performance

Basic Parameters: (1) (2) (3)

Normal Operation6 panels, no wind

Emergency Op- Maximumeration 5 panels, Wind 6 panelsno wind

Effective Height - ft.

Static Capacitance - lJ.f

Resonant Frequency - kc

Performance Characteristics:

628

.1637

32.28

625

.1412

33.05

684

. 1515

30.68

(15.5 kc, 1000 kw radiated)

3 db Bandwidth - cps

Base Reactance - ohms

Base Voltage - kv

Top Hat Voltage - kv

Input Current - amps

Radiation Resistance - ohms

Average Gradient - kv / mm

Maximum Gradient

With Coupling Circuitry:

38.2 32.7 43.5

-46.9 -56.7 -47.7

123. 144. 113.

160 185 152

2545 2559 2336

.154 .153 .183

.43 .52 .43

.74 >.84 1. 30

Maximurn operating freq. - lec

Miscellaneous Data:

Apparent Inductance - !J.h

Antenna Q (15.5 kc)

29.45

149

406

6-2

164

474

28.25

171

356

DECO 43-1 630226 BR

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FREQUENCY - KC

3D 4»

Flaure 6-1 BASE REACTANCE AS AFUKCTION OF FREQUENCY

6-3

range of operating frequencies referred to the bushing entrance. Note

that the resonant frequencies (zero reactance) indicated in Figu.re 6-1

differ slightly from the tabulated values taken directly from. model data,

reflecting the corrections and different reference point involved in the

figure.

Considering the re:;uUs of the rn.odcl study, the configuration

selected adequately llleets the design goals. The bandwidth require­

ment (not to be less than 37.5 cps) is exceeded slightly under normal

conditions and only degraded under elllergency operation where such

degradation was considered acceptable. Silnilarly, the maxilll Ulll

operating frequency (not to be less than 28. 5 ke) was exceeded by

almost 1 kc under normal operation and violated only under maximum

wind distortion by 0.25 kc. In all cases considered, the average gra­

dient on the antenna conductors fell below the design limit (average

not to exceed 0.65 lev /mm), with the lllaximum value exceeding the

tolerable limit (maxirnuln not to exceed 0.80 kv/mm) only for full­

power operation with 5-panels and for m.axilnum wind distortion. Since

the full-po-'lIer requirement is relaxed for 5-panel operation, this rep­

resents no problem. ~imilarly (sec Seciiull J. 3. 1) t!-;.~ ~::;:C~GG gl'adieiit

under wind distortion was not considered intolerable considering the

relative infrequency with which su.ch such high winds are incident to

the site.

6-4

Appendix A: MODEL DATA

This appendix contains the data obtained on the VLF-PAC model

during the measurement program. Table A-1 presents the effective

heights, static capacitances, and resonant frequencies for Tests 21

through 39; tower heights, number of panels, and dates of tests, are abo

included. Table A-2 presents a tabulation of the base reactances meas­

ured on the model at various stages of development.

Detailed descriptions of the test procedures and theoretical back­

ground are given in other sections of this report; however, certain com­

ments are repeated here for refercnc8.

o Effective heights - An average was taken of several runs

made on each test. This average was corrected for the effect of the input

susceptance of the cathode follower driving the voltmeter.

• Static capacitances -- The average of several readings was

divided by 1. 027 to correct for the effect of the wires on the model being

slightly larger than 1/100 of the full-scale size.

• F_e5C'~~~t freq'.le~cips - The resonant frequency was obtained

by interpolating to the frequency at which the measured base reactance was

zero.

• Measured base impedances .- The resistive term is tabu­

lated for completeness only, but should not be considered indicative of radia­

tion reRistance or full-scale losses because of the i.nability to accurat.ely

model ground plane and cable conductivities.

A-1

TABLE A-1

Model Data Summary

TestNo. Date Test Conditions

21 2.9 Mar. 162 TIErnerg~ncyll o?eraticn :,;ingle bushing, .Modeled T /KBSee Note 3

22 2 Apr. '62 "Normal" operation, sir gle bushing

23 II May '62 T / HB enlarged. two bus :lings

24 Z3 Ma~,r '62 T/HB enlarged, two bushings

20 25 May '62 T/HB enlarged, two bus:ungs

26 28 May '62 Ne-w top hat with inc rea.:: ed sags

27 31 Ma~r '62 New top hat with increa~ed sags

28 1 June '62 New top hat with inc rea! ed sags

29 6 June '62 Raised "B TI To·......·er 2.0'

30 6 June '62 Raised "Bit Tower 2.0'

31 7 June '62 Raised '13" Tower 2.0'

::.>32 7 June '62 Meaaured at Hoor T /HB through one bushing

I 33 B June '62 "Block and Tackle" in:3t3.11ed on Panel "AnN

'62 Revised dov.nlead pull-eli structures to 4-1egged version34 14 June

35 26 June '62 36 wood poles in place f:;lr willa distortion

36 9 July '62 130 mph wind distortec. :ondition

37 27 July '62 Critical fan-to-guy spacing (Panel "D tl) increased to 45'

38 2.8 July '62 Critical fan-to-guy spacing (Panel "D") increased to 70

39 12 July '62 Observe shift in resonant frequency due tosimulated tuning networ:<:.

MeasuringPoint

(Note 1)

a

b

b

b

d

a

b

Effective Static ResonantHeight Capacitance Frequency~ (£eO!t) Co hJ.f) f, (kc)

625. 0.1451 33.05

625. 0.1633 32.18

637. 0.1647 29.60

6L;J,. 0.1634 33.70

622. 0.1634 32.25

610. 0.1642 32.45

607. 0.1638 33.57

608. 0.1647 29.43

623. 0.1644 29.45

627. 0.1630 33.85

629. 0.1633 32.45

627. 0.1630 31.95

629. 0.1630 31. 95

628. 0.1638 32.28

619. 0.1640 32.28

685. 0.1575 30.68

See Note 4.

See Note 4.

28.25

C1271 ieet12'71 ieet

2.

Notes:1. Measuring Points

a. :-rormal, at Transmitter /Helix Building floor.b. Through sirrr.ulated tuning/coupling circuitJ y.c. At tie bar between two entranc e bushing s.d. At T::-ansrnitter/Helix Building floor. with only one t:ntrance bushing used (as for eme::gency operation).

The full-scale tower heights were as follows.

A BTest:=; 21-28 996' feet 1175 fet:tTests 29-39 996 feet 1195 feet

3. All tests ...... ere for 6-panel operation, except tt st 21, "...hicb was run with 5 pa:c.els.4. Tests 37 and 38 ......ere for gradient studies only.5. Corre:ted model antenna data scaled to full-sized anter.na.

6. Tests 21 through 25 for Top Hat 1; 'ests 26 thlough 28 for Top Hat Il; tests 29 through 39 for Top Hat III.

TABLE A-2

Measured Base Impedance (Referred to Full-Scale Antenna)

TEST 21

FrequencyKC

10. 0012. 4514. 0017. 5020. 0022. 5025.0527.5030. 0031. 00

TEST Z2

ImpedanceOhms

0.21 - jl02. 00.20 - j77. 9

NR - j66. 10.36 - j47. 20.41-j35.0O. 50 - j2.6. 90.55 - j19.80.65 - j13. 10.79 - j6. 870.85. - j1. 81

FrequencyKG

31. 5032.0032.5033.0033.5034.0035.0037.5040.00

IrnpedanccOhms

0.86-j3.820.89-j2.190.91 - j1. 540.92 - jO. 150.97 + jO. 750.99+j1.801. 03 + j4. 001. 2.0 + j8. 551.40 +j13.0

Frequency ImpedanceKC Ohms

10. 00 ------:O,.....--:-176-_-:-j8=-8:-.-0=--

iZ.45 0.24 - j66. 714.00 NR-j57.117.50 0.32 - j38. 92.0.00 0.40 - j30. 0ZZ.50 0.48 - j22.. 725.05 0.55 - .i15. 627.50 0.62-j9.8330.00 0.76 - j4. 33

TEST 2.3

FrequencyKG

31. 5032.0032.2532.5033.0035.0037.5040.00

InlpcdanceOhms

0.85 - j 1. 430.88 - j O. 410.88 + jO. 0(,

0.90 + jO. (,2.0.92+j1.501. 01 + j5. 231.20 +jl0.01.40tj14.0

FrequencyKC

10.0014.0020.0025. 0028.90

NR - No Reading

ImpedanceOhlTIS

NR - j86. 0NR-j50.0

0.40 - j26. 00.65 - jl1.20.79 - .i2. 1

•

A-3

FrequencyKG

29.5029.6030.0035.0040.00

ImpedanceOhms

0.80-jO.30.81 +jO.0.82+j1.31.10+j11.71.50 +j21.0

TABLE A-2 (Cant.)

TEST 24

FrequencyKG

10.0014.0020.0025.0030.0012.0U

ItnpedanceOhms

0.23-j86.00.30 - j55. 70.40-j31.00.59-j17.60.79-j6.670.88-j3.12

FrequencyKG

33.5033.7033.7534.0035.0040.00

IrnpedanceOhn1s

O. 92 - j O. 300.95+jO.0.92+jO.10.93+jO.591. 01 + j2. 881.42 +j10.8

---------------------------------------------------------------------------TEST 25

Frequency ImpedanceKG Ohms

FrequencyKG

Itnpedanc eOhms

0.90-jO.63O.')O+jO.1.02 +j5.291. 58 + j 13. 5

12.0032.2535.0040. 00

10.00 0.25-j85.014.00 NR - j55. 020.00 0.42 - j29. 525.00 0.49 - j15. 630.00 0.80 - j4. 66---------------------------------------------------------------------------TEST 26

FI'cquency ImpedanceKC Ohms

FrequencyKG

ImpedanceOhins

0.80 - j O. 780.89 I j O.1. 00 + j4. 851.52 +j13.4

32.0032. 4535.0040. 00

10.00 0.18 - j85. 014.00 NR - j55. 020.00 0.41 - j29. 525.00 0.58 - j15. 8

:?g:gg----- ~:77_ - j5. 00--------------------------------------------------

TEST 27

Frequencyl<;C

10. 0014.0020.0025.0030.00

ImpedanceOhms

0.18 - j85. 5NR-j55.7

0.39-j31.0O. 57 - j 17. 20.77-j7.00

FrequencyKG

32.0033.5533.6035.0040.00

Im.pedanceOhlns

0.86 - j3. 10.90+jO.0.91 +jO.0.99 +j2.H61.45 +j1L5

------------------------------------------------------------------------.-

NR - No Reading

A-4

TABLE A-2 (Cont.)

TEST 28

Frequency Impedance Frequency InlpedanceKG Ohms KG Ohms

10.00 0.18 - j82. 0 29.40 0.79 + jO~

14.00 NR-j51.4 29.45 O.80+jO.20.00 0.43 - j25. 5 30.00 0.81 -\ j1. 325.00 0.61 - jiO. 4 35.00 1. 07 + jE. 029.00 0.78 - jO. 86 40.00 1. 53 + j21. 5---------------------------------- ---------------------------------------TEST 29

FrequencyKG

10.0014.0020.0025.0029.0029.45

ImpedanceOhms

0.20-j87.5NR - j52. 1

O. 45 - j 25. 50.b1-jl0.80.80-j1.00.82 + jO.

FrequencyKG

29.5029.6029.7030.0035.0040.00

bnpedanceOhms

O. 81 + j O.0.81+jO.340.82 + jO. 60O. 83 I j 1. 3

1. 09 + j1l. 01. 58 + j21. 8

-------------------------------------------------------------------------TEST 30

FrequencyKG

10. 0014.0020.0025.0030. 0032. 00

ImpedanceOhms

0.20 - j86. 5NR - j56. 1

0.40 - j31. 5O. 58 - j 18. 00.79-j7.140.88 - j 3. 28

FrequencyKC

33.6033.7533.8535.00

40.00

bnpcdanccOhms

0.93 - jO. 41)

0.94 - jO. 10.95+jO.01. 01 + j2. 01.48 +j10.5

--------------------------------- ------ ---------------------------------TEST 31

FrequencyKG

10. 0014.0020. 00

ImpedanceOhms

0.20 - j85. 5NR-j55.0

0.41 - j29. 5

FrequencyKG

25.0030.0032.45

IrnpcdanccOhms

0.59 - j15.80.79 - j5. 000.90+jO.

--------------------------------------------------------------------------TEST 32

FrequencyKG

31. 9532. 1532. 30

Im.pedanceOhms

0.89+jO.0.90 +jO.31.0.90 + j O. 62

FrequencyKG

32.4034.00

IlTlpedanceOhms

0.91 +jO.771. 00 + j4. 11

-----------------_._-------------------------------------------------------

NR - No Reading

A-5

TABLE A-2 (Cont.)

TEST 33

FrequencyKG

31. 95

IITlpedanceOhms

0.90+jO.

FrequencyKG

lrnpedanceOhms

-------------------------------------------_ .. _---------------- .. _--------TEST 34

Frequency IITlpedance Frequency ImpedanceKG Ohms KG Ohms

10. 00 0.23 - j85. 0 32.00 0.89 - jO. 6214.00 NR - j55 32.28 0.90 + jO.20.00 0.42 - j29.5 32.45 0.91 +jO.4625.00 0.58 - j15. 8 35.00 1. 03 + j5.:l.4~~:.~~ ~'-~~_-_ j~:.~? -:'O_,_~O J:.52± jJ.}.. 'L __

TEST 35

Frequency bnpedance Frequency ImpedanceKG Ohms KG Ohms

32. 00 0.88 - jO. 6232.28 0.90 + jO.

~~~~~---------------~:.~~-~j~:.~~------------------------------------------­TEST 36

FrequencyKG

10.0014. 0020.0025.0027.0030.00

ImpedanceOhITls

0.19-j87.0NR-j55.0

0.49 - j28. 50.68 -j13.20.79 - j8. 150.93 - j1. 5

F"equencyKG

:1U.~U

30.6830.80:15.0040.00

ImpedanceOhITls

... r.... .""?")v. '1':) ... JU. J-J

0.98 + jO.1.00+jO.321. 24 + j9. 712.20+j16.0

--------------------------------------------------~-----------------------

TEST 39

FrequencyKG

10.0014.0020.0025.0028.0028.25

ImpedanceOhms

0.22 - j85. 0NR-j52.~

0.53 - j24. 50.72 - j8. 400.90 -jO.540.91 + jO.

FrequencyKG

28. 5029.0030.0035.0040. 00

ImpedanceOhms

0.92 +jO.700.97 + j2. 11. 02 + j4. 341.32 +j16.32.17 + j24. 3

---------------------------------------_ .. _-------------------------------

NR - No Reading

A-6

Appendix B: PERFORMANCE RELATIONSHIPS

Short, capacitively loaded antennas of the type considered in this

report are conveniently characterized by the antenna capacitance C anda

The antenna capacitance deterrnincs the inputthe effective height h •a

reactance (for frequencies much below resonance f ) and, hence, the volt­a

a ges which result from the current developed on the radiator. The low

values of radiation resistance R which result from short antennas requirea

large currents to develop appreciable quantities of radiated power. The

top loading, then, is a practical necessity to luaintain tolerable voltages

under this situation and also, as will be shown, a vital factor in provid­

ing sufficient radiation bandwidth bw .a

Effective He.ight

The effective heigl,.; depends jointly on the physical length of the

vertical radiator and on the current distribution. If the current clistri-

bution as a function of elevation z is I(z) and the physical height is II,

then

ha

1

Ia

II

Xo

I(z) clz . (.13-1)

Where Io

1(0), i. e., the value of the base current.

For a short, thin radiator I(z) tapers linearly frorn a maxirnum

at the base to zero at the top so that

ha

H/2 (Short, Thin Monopole) (B-2)

However, if the top loading capacitance C is increased sufficiently,o

the effective height may be made to approach the physical height.

H (B- 3)

B-1

Practically, the effective height is considerably less than the phy­

sical height as a result of both a practical limiation on antenna capaci­

tance and, more important, a loss in effective height resulting from cur'­

rents in grounded towers and guys. As an approximation, the gross effect

of the oppositely sensed (with respect to the downlead current) currents

in grounded structures may be considered as altering the current distl'i­

bution, I(z), and thereby reducing the effective height.

An alternate definition of effective height which lends itself to two­

terminal measurements is in terms of the open-circuit base voltage Vb

and the incident, vertically polarized, electric field E .•1

h '" Vb/E, • (B-1)o 1

This definition is identical to Equation B-1 for short antennas. Equation

B-4 is easier to apply experientally since it requires only two measure­

ments, (i. e., base voltage and incident field) whereas Equation B-1 re­

quires a knowledge of all currents on the antenna and nearby structures.

Radiation Resistance

The radiation resistance R is defined in terms of the antenna base

current 1 and the radiated power P •o 0

R = P /12 ohms •o 0 0

(B-5)

Here P is the summation of the incident power over a closed surfacea

surrounding the antenna.

For short monopole antennas, the radiation re sistance is given

by

R = 160 n 2 (h /A)2 ohmso 0

B-2

(B-6)

Considering Equations B-2, B-3, and B-6, it becomes apparent

that top loading can increase the radiation resistance by as rnm:h as fOL~r

times. This result may be obtained by integrating the total radiated power.

Although this integration can theoretically be performed over any converi­

ient surface, it is simpler to develop far-field (Fraunhofer Region) ex­

pressions for the radiation field and perform the summation of incident

power essentially at infinite distance.

Base Current

Having determined the radiation resistance, the base current can

be expre ssed in terms of the required radiated power P •o

Top Hat Voltage

I = ~ P /Ro 0 0

alnps. (B-7)

Referring to the basic equivalent circuit shown in Figure B-1,

the voltage at the top hat (V) appears across the antenna capacitance.t

Resonant Frequency

V - I fmC volts.t 0' 0

(B-8)

Since the antenna and downleacls have some inductance, the antenna

will have a resonant frequency f given bya

Base Voltage

fo

12n"fLC cps.

o 0

(B-9)

Using the resonant frequency, the base voltage Vb is related to

the top hat voltage as

B-3

~

~> Ro = RADIATION RESiSTANCE•

DEtD 43-21 630412 TH J.

Lo = ANTENNA INDUCTANCEI

: ~ 1. Co 0 ANTENNA CAPACITANCEI 0

III

1 .""T vV

I RL = LOSS RESISTANCE

Figure B-1 BASIC EQUIVALENT CiRCUIT

B-4

(B-10)

Thus,the base voltage is less than the top voltage for frequencies below

resonance and approaches zero (i. e. limited only by the relatively sluall

resistance) at resonance. Equations B-8 through B-10 neglect the effects

of the resistance since, for short antennas, they are not significant in

determining the lUagnitude of the input impedance.

Antenna Q

The bandwidth of the basic antenna, neglecting loss resistance

R L is derived frolU the antenna Q, where

Bandwidth

Q 1/wR Co a

(R-11)

The half-power bandwidth (bw ) for the undalupcd antenna is theno

given by

bwa

fQ

wR C f cps.o a

(13 -1 Z)

The actual bandwidth bw of a particular antenna is greater than

the value indicated by ~quatlOn B-iZ. Ab ct i"coulL vI Lhe dalUping effect

of loss resistance R L , where R L is referred to the antenna circuit as

shown in Figure B-1. Under this condition, the operating bandwidth is

inversely proportional to the radiation efficiency 11,

bwbw

a(B-i3)

Here the radiation efficiency is given by:

Ro

R+R~a

usually expressed as a percentage.

B-5

(B-14)

Conductor Surface Gradient

Figure B- 2 depicts a typical cylindrical conductor section whose

length L is much greater than its radius r, all dimensions being much

less than the wavelength A. The relation between the displacement cur­

rent density and the electric field gradient at the conductor surface will

be developed in terms of measurable quantities.

Writing Maxwell's first equation,

curl H oE +aE

€­at (B -15)

0"", for" RinllRoirlr111y tiTIlA varying fiplrl,

curl H = oE + jW€E • (B -16)

If we further restrict 0 = 0 for application to the non-conducting space

surrounding the conductor,

curl H = jW€E • (B-17)

At the sU~'face of a perfect conductor, only the normal component

of the electric field is present E. For this component, which is orcli­p

narily referred to as the gradient,

curl H = jw€E (B-18)P P

(Note that E is the generalized vector, E being the p component. )p

Expanding,

curl HP

jw€EP

(B -19)

This is further simplified by noting that for a long conductor

HZ 0, reducing the expression to

-jW€ EP

B-6

(B-20)

Deco (3-21 6S0~12 TH B

p p

Ep =SURFACE COMPONENT '"OF ELECTRIC FIELD~

IT)

f),ZIL

II+~I>, .,Z7 _ I

r ItoI

-..J

Fi gura B-2 INCREMENTAL SECTION OF A LONG CONDUCTORSHOY/IN:] CYLINDRICAL CO-ORDINATE SYSTEM (p, cf;, Z).

Near the 'surface of a long thin cylindrical conductor carrying

current at a low frequency such that the radii of interest are luuch less

than the radian length (1' < < A/ Zn) the quasi- stationary field predominate s

and is given by

IZ

H 1 = -- amps/meter •rp Znr

InR",rting thiR relation into F:qnation B-ZO yields

(B-2! )

IE Ip

1 dIZ2nrWE: ClZ volts/meter. (B-22)

Since the magnitude of the radial field is the critical factor in

corona formation, the absolute value is given in Equation B-2Z.

In practice, the partial derivative in Equation B-Z2 can be approxi­

mated by measuring the change in current (£'lIZ) over a small but finite

increm.ent of conductor length (6Z). Thi s yields a useful approximation:

(B-23)

Equation B-23 yields the conclllrtr,,' Rllrface gl·adip!').t Or!. <:\n incre-

mental length of conductor. If a large number of similar conductors are

involved, as in an antenna top hat, it i8 useful to be able to obtain an aver-

age value of the surface field. For thi"s purpose, the incremental quan­

tities l'IIZ

' 6.Z are replaced by the total base current 10

and the total length

of elevated conductor L. This yields the average gradient

1 IE = -Z-- ( La ) volts/meter.

p nrWE:(B-24)

Obviously, if the incremental displacement per unit length 6.IZ

is uniform,

then Equations B-Z3 and B-Z4 give identical results. "In practice, however,

it is not usually possible to maintain a uniform gradient, so that the value

given by B-Z4 is a rough approximation useful only for estimating

purposes.

B-8

Appendix C: ANTENNA EQUIVALENT CIRCUIT

The use of equivalent circuits simplifies sonle antenna probleITIs

by characterizing a physical structure involving distributed parameters

by a IUITIped-parameter equivalent. VLF antennas of the type considered

in this report are represented approximately by a simple series L-C cir­

cuit with small series resistances representing radiation and loss com­

ponents. The resistance properties depend strongly upon the frequency,

so that the equivalent resistance must also vary with frequency. How­

ever, the equivalent reactive cOITIponents are relatively independent of

frequency, so that one circuit can be used to describe the reactance

properties of the antenna over thc entire frequency range.

Figure C-1 (A) shows a simple or basic equivalent vlf antenna

curcuit consisting of lumped inductance L o , capacitance Co' and resist­

ances Ro , R L • Except for the previously noted variation in the resistance

values, this circuit is usually a close approximation for any vertical

radiator whose length is short compared to a wavelength. A convenient

technique for handling iITIpedance data £rOITI such a circuit is shown in

Figure C-1 (B) in which the base reactance-frequency product is plotted

as a function of frequency squared. For this circuit, the input, or base,

reactance-frequency product is

fX 2nLo fl - 1 / 2nCo (C-1)

which is linear in f2, with a zero-frequency intercept of - 1/2TTCo

and a slope of 2TTLo ' as shown in Figure C-1 (B). For this circuit, the

static capacitance Co and the resonant frequency fa provide two easily

measured points which determine the reactance at any frequency at

which the antenna cur rent distribution is approxiITIately linear.

C-1

DECO 43-21 63040B TH A

f2 _ fREOUENCY SQUARED

/INTERCEPT = de;

I Lo = ANTENNA INDUCTANCEI

~ Co = ANTENNA

! JCAPACITAUC[

WRo = RADIATION

I RESiSTANCEI

II R

l= LOSS RESiSTANCE

IACCESSiBLE TERMINALS

(BUSHINQ ENTRANCE)

';:'z +~

T~w- ~...

!I'

wuz~

~

u~u,n'W

'"~'"

=: 0- I 2o

(A)

F1aure C-1( B)

BASIC EQUIVALENT CiRCUIT

f 2,f2 - FREQUENCY SQUARED

D -

~

,/ ACTUAl 1NTERCEPT =/ I

~ 2rr(Co+Cb)/ I

,/ EXTRAPOLATEO INTERCEPT = b!c+-------1- 0

wuz~

>­u~

w-

- ,§ T SLOPE - 2rrl o=> ., +----------"JI"

~ !~ I

I RL = LOSS RESISTANCEI

ACCESSI aLE TERMI NAlS

(BUSHING ENTRANCE)

(A) (B)

Fliure C-2 REFINED EQUIVALENT CIRCUIT INCLUDING NEAR-BASE CAPACITANCE

C-2

It was found that extensive data taken fron1. base-reactance meas-

urem.ents on the scale vl£ antenna m.odel described in this report showed

an appreciable departure from. the expected values indicated by Figure

C-1 (B), particularly as the frequency approached zero. Precise meas­

urernents of the static capacitance (Section 2.2.2), and the base react­

ance in the operating frequency range (Section 2. 2.3) revealed an appar­

ent excess capacitance at the lower frequencies. This suggested an

additional capacitance element in the equivalent circuit across the input

on the input. side of the antenna inductance. This additional capacitance

C b is referred to as "near-base" capacitance.

Figure C-2 (A) shows a refined equivalent circuit includine rI.

near-base capacitor. This additional capacitance is attributed to the

long, horizontal busses and the insulators and support structures

associated with the buswork over the Transm.itter /Helix Building. For

this model, the near-base capacitance is much less than the antenna, or

top hat, capacitance. For this situation, the variation of reactance with

frequency in the region near resonance is relatively independent of Cb.

Thus, as shown in Figure C-2 (B), extrapolating frorn the near-reso-

pGX"tiOrl of the rcu..ctancc-fi:c:;qu-C;JH... y \...UL·Vt:: :-.;huulJ yield a zero-

frequency intercept depending only on the antenna capacitance, that is

- 1/2TTCO ' The actual intercept, however, will yield a value related to

the sum of both capacitances,

Lim fXt~O

1(C-2)

The above discussion descrihes one technique for deriving a

three-element equivalent (reactance) circuit from measured data.

This proc.edure was applied to model data and found to provide an accur­

ate representation of the reactance variation with frequency.

C-3

In the developrnent of the equivalent circuit, it should be noted

that two rninor corrections were applied to the Inouel base-reactance

data:

(a) Corrected data is referred to the bushing entrance point

rather than the T IBB floor terrninal. Cornpa.ring data frorn Tests 30

and 31 reveals an equivalent inductance of approxirnately 11.3 f.Lh (full

scale) for the floor-to-bushing rnodellead. This arnounts to about 1. 4

ohms at 15.5 kc.

(b) The model wire diameter was 1. 4 times the scaled diameter.

This inc rease model capacitances by approxirnately 2.7 percent. The

corrected data reflects an appropriate reduction.

The base reactance data of Test 34 (referred to full scale) is

shown in Figure C-3 to i.ndicate the way in whi.ch the equivalent circuit

values were determined. The plot of the base reactance-frequency

product as a function of frequency squared shown in Figure C-3 exhibits

the departure from a straight line previously noted. Specifically, the

actual zero-frequency intercept indicates a static capacitance C a of

0.1711 Il-f while the near-resonance extrapolation indicates only 0.1530

f.lf for the antenna or top hat capacitance Co' The difference, 0.0181 Il-f,

is attributed to near-base capacitance Cb. Correcting for the wire­

diameter modeling discrepancy yields:

Co = 0.1490 f.Lf

Cb = O. 0 176 J.Lf

C a 0.1666 f.Lf

The resonant frequency fo becornes 33.8 kc after the data is

referred to the bushing entrance point. Note that the wire diameter

discrepancy does not change the resonant frequency due to compen­

sating changes in inductance and capacitance.

C-4

IIEtO 0-21 LHUa tM A.

tHeI1D~lOCO'00600.00zoo

iJd - l-f--

iHOlE: lE1l 31 WI REF!IREo 10 BUSHIHO E'M;~If IULl·SCUE IMTUU

~--

I

/•I~ MEU lESOHUC£ -

"·f ~I-I H'.'

11.46 I 10' I

~_.--

p

/

f- Ir---- --~- --

..~. ---- ----- c----

1--------- .. w'/ ~-- - - - --- -~

,/../"

1----- ----- -"1/ -- ---- --- --- ---

[/ 1...

~t~ :-1--' ---

..""/

t ' I~/i~ --G ~ ---

9~D__ 1 10'·- 2-(C.'C,) I h

( I

=--E' 1iJ211C o

I

200

3BO

'00

-600

10.

-IOC

- 500

-300

- 200

·BOO

-900

'1100

o

-I DOG

FHQU£MCl 1M ~C SQUARED

Figure 0-3 DERIVATIUN OF EQUIVALENT CIRCUIT

C-5

The effect of the additional near-base capacitance on the perform­

ance of the antenna is not great for the val.ues obtained. The apparent

effective height becomes slightly frequency dependent because of the

loading effect of the near-base capacitance. However, this will only

result in a variation of about 5 percent over the frequency range of

interest. Compansating changE:s in apparent effective height aUlI Htatlc

capacitance introduced by Cb result in the saTTle unloaded antenna band­

width. Other performance characteristics reflect negligible differences

when cOlllputed from the circuits of Figures C-1 (A) and C-2 (A).

C-6

Appendix D: INVESTIGATION OF VLF FIELD DISTRIBUTION

The distribution of surface current density (H··field) and the

distribution of vertical electric intensity (E-field) were determined in

the central region of the scale model. In accordance with Navy dlrec··

tions, the area inve stigated was limited to that in the immediate vicinity

of the Transmitter IHelix Building and a sector under one downlead.

Figures D-i and D-2 indicate these general areas as well as the nlodel

T IRB configuration during measurements. Within the limits of the

structural variations considered in the model program, the final shape

of the building and the top hat are not expected to create any significant

differences in the r~sults. While the hoist hou::;e::; at the T IHB were not

included at the time or modeling, any deviations of current magnitudes or

directions crea.ted by their addition in actual installation are not expected

to be of any prinlary consequence.

Figure D-i shows the distribution o[ surface current density ill

the vicinity of the T IBB with the magnitudl~ given in amperes per meter,

normalized to a base current of 2540 anlperes, with the direction of sur­

f::.rp rllrnmt inrlicated at each point of nleasurem,,:nt.

In the near vicinity of the T/I-IB, the H-field distribution is sym­

metrical about the center Hue. Beyond the influence of the building,

field symmetry is governed by the distribution of towers and guys. Near

the center tower guys, 120·degree sectors of symmetry center along the

center tower guy planes; in the vicinity of the intermediate lowers and

beyond, 60-degree sectors of sym=etry center along radials passing

through eaL:h 11llel'11lediate tower.

In addition to the field distribution on the roof and grotmd =at,

shown in plan view in Figure D-1, the magnitude and direction of current

D-i

/'

AI,

~~

"~~ ;( .;~ 0••>~N

H;·d\

fI~"~.'~o•

II

y,I ..~

; It' :;..../ j;'/,r t~1//

/ ..'I .:f

~/ ;t

,I

¥I =;/

I

:< H/'

~f

t~

i"

~f

t~

:fb

D-2

C!I:zc::l....::>ID

><

-'LU

="-a:..............=:IEv.>:z:-ea:.....u.10

:r

>-=::z:

=>-LLJ. :>:;.._.

;z:

::zc:>

.....ID

a:.....v.>

CI

=....UJ

lL-I=I

cCD

,..,bIl

.....

I .~~~0

',".",:~.;,\!

~, .' ¥• ~. :-:.

t. j. ~. :.

;. j-'

=a::>

....c::>

>­UJ

=t--

....1....

NI

CI

L~,

D-3

"

Q)...:::JbIl

......

dens ity is also shown along the center line of the T /HB exterior walls.

Radio frequency currents display a tendency toward concentration in the

salient areas of irregular conductors (i. e. , those protruding beyond a

circle of equal area). This effect is indicated in Figure D-1 by a plot

of surface current density along one side and to the center line of each

end of the T/HB exterior. Loss studies which guided the distrihl1t;Cln of

conductors on the T /HB and in the ground system immediately beyond

were based on the mea~ured data. In accordance with the field data, the

ground system design displays a concentration of buried conductors near

the building corners and some departure from true-radial directions in

accordance with the measured magnitude and direction of surface current.

Figure D-Z is a plot ofE-field distribution near the surface in the

vicinity of the T /HB. The electric fielc'l magnitude at each point of meas­

urement is given in volts per meter and is norrnal to the surface. Axes

of E-field symmetry exists identical to those previously described in the

I-I-field measurements. The values shown are normalizec'l to full power

operation at 15.5 kc.

Although measurements of E- and H-fields in typical sectors

beyond the T/HB vicinity and the exploration of tower and guy resonances

were originally proposed, they were deleted at the direction of cogniy,ant

Navy offices. It was felt that tLe similarity with the existing Cutler

facility was sufficient to preclude the need for such studies.

D-4

Thb r('pOl'~ pr('"enl'-' the l"l'"ults of the i1ntC'llna. nlodcl study which

was c~Lled out for the development of t.he design of the VLF PAC antenna.

Beginning with an evaluation of the initial coniiguration (Section 5. 1) this

study includes the results of a continuous modd program involving

detailed structural revisions which occurred as part of the refined design.

These revisions included changes in top hat shape, intermediate tower

elevations, entrance bushings and Transmitter/Helix Building. In gen-

, ' •. e:tal, thE!"""eIfrcr;-6f such revisions were reflected by relatively minor

changes in electrical performance as derived f~~m model measurements.

Consequently, the measurement of some aspects~f perform~ncewhich

were not considered of primary importanc e or were not expected to I

change appreciably were not repeated for the final revisions.

For comparison, Tabie 6-1 summarizes both the predicted full­

scale basic antenna parameters and the derived operating characteristics

relating to full-power (1 megawatt radiated) operation at the design

frequency (15.5 kc). This data is given for (a) normal (6 panel, no wind)

operation, (b) emergency (5 panel, no wind) operation, and (c) for the

condition r ~ 6 panels and maximum wini! (1.30 mph) distortion. The

normal and wind-distorted data w"re obtained from the final model

with all pertinent revisions included. However, the emergency con­

dition was evaluated only on the initial configuration. Since no major

changes w~re determined in the performance for the normal condition

(compare, for example, the results of Tests 22 and 34) it was consid­

ered unnecessary to repeat the enlergency condit~on measurements.

The base reactance values shown in Table \-1 include all

corrections and nrc rcfcrrcJ tu the bushIng ('nt 1 <ir]l'~ on Ih(' antenna.

Figure 6-1 is a plot of the corrected input reactande over the entire\\

. 6-1

E-Z

--,.,-0.... -­....-"" ....COl --zu::0 N........II

"">c:a :00:c::>=- .....oa­z:z::z_... --­Z"C

•...........:::>.......

r----------- ....-----DECO 43-1 63D226 8ft

... . . j

~~-~~:- L-~~_.~_:--, ,•,

o

20

-80

· , ' . , '. " , ,. , ,. ·i·",t·, .I,lt!':'• • : ; •• ; •• ·'1 '. ' ~ ~ "~ ••••, •• !., •• :. I.: .. ,~. td t i·H 11+. '.,.",j.'J •.•.••• ,',! "'.. +I"".'I'.III"'·lIjl\l+Hi:'· ,I.." " , • i I' ,01 I •Wj 1 jqtttfu~'~ 7'~. ;. ;. ~;- :'~~' :-:-~0- 1.-:.~.:-t I. ;. i. t. rttt.i. I 111 LIi II' 11tl.:: : : : :1' 'I . 'p' 'IL"',; :;;;! II.;; \ltitjj.;.r'Ulj+l:,.".\ S X UE S, p "r,ltt:· ':t·~,~~i'!'i!:

t-----+--+-t--......~i ... .. ~ ::;: i ij!30 MPH .'"D II !J I, ttIH~~ ~ iW~I~'l.:t' .t.: t__~ ~-i,j. ,~.~ lLLrl1

j .1; 1\: j 11 • l! l;~~' .HI tl l~+", , •• ,,",' 1"\.llllilo"~'~1 IlIITI'+ it' .,. " , , : : I ' I! II'.! I,,:r l.' I.. ':j . j t q;1 1

• , I , , I ' !.." ri J.I ,j , . t· + , I II.,I'"" i',)1 'l; LJ"r!'qt" Hilt l '

-20 Hr-+............---1I--l------+-+-"-~- .......+_'_H-l~~FH~\I-H+++-H+~-+++H-I+~! ' I j , : ; i [1 •IU ru~ 4'1 1 j 1 I;; :; , j I j : : , : uJ...~~~t:·ft~'f1+rl1ffilftjjtfH:81'Htt±fHt'~' iffiffil:1I--l----<r-I--l--j--f-+-....-l- . ..J,J-.,.j,~''''''1<:

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FREOUUCY - IC

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- --Fllur. 6-1 lASE REACTANCE AS A FUMCTIOM ~F FREQUEMCY

As an example of the detail obtained in this study, consider the

photographs appearing in Figures E-2 and E-3. Figure E-2 shows an

overall view of the model under maximum wind distortion with the

obsE:rver looking toward the center tower from just beyond an outer

tower of panel No.2. (The large bright spot near the upper part of

the photograph is caused by the moon.) This study was made with 30

kv excitatiun. Faint traces of corona are visible on the panel with

brighter indications along the No. 2 panel downlead where it approaches

the center tower guys to within 20 feet. Figure E-3 shows a close-up

of the critical downleads (two panels are distorted identically under the

wind condition studied), indicating clearly the extent of corona in this

area.

Further study of thl, problem areas was carried out using the

current distribution method to develop quantitative information relating

to corona formation.

E-4

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