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YOU'RE HEARD, LOUD AND CLEAR.

8625 Industrial Parkway, Angola, NY 14006 Tel: 716-549-4700 Fax: 716-549-4772 [email protected] www.bird-technologies.com

Installation and Operation Manual for

T-Pass Transmit Multicouplers

73-90-11 Series

Manual Part Number

7-9100

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Warranty

This warranty applies for five years from shipping date.

TX RX Systems Inc. warrants its products to be free from defect in material and workmanship at the time of shipment.

Our obligation under warranty is limited to replacement or repair, at our option, of any such products that shall have

been defective at the time of manufacture. TX RX Systems Inc. reserves the right to replace with merchandise of

equal performance although not identical in every way to that originally sold. TX RX Systems Inc. is not liable for dam-

age caused by lightning or other natural disasters. No product will be accepted for repair or replacement without our

prior written approval. The purchaser must prepay all shipping charges on returned products. TX RX Systems Inc.

shall in no event be liable for consequential damages, installation costs or expense of any nature resulting from the

purchase or use of products, whether or not they are used in accordance with instructions. This warranty is in lieu of all

other warranties, either expressed or implied, including any implied warranty or merchantability of fitness. No repre-

sentative is authorized to assume forTX RX Systems Inc. any other liability or warranty than set forth above in con-

nection with our products or services.

TERMS AND CONDITIONS OF SALE

PRICES AND TERMS:

Prices are FOB sellers plant in Angola, NY domestic packaging only, and are subject to change without notice. Fed-eral, State and local sales or excise taxes are not included in prices. When Net 30 terms are applicable, payment isdue within 30 days of invoice date. All orders are subject to a $100.00 net minimum.

QUOTATIONS:

Only written quotations are valid.

ACCEPTANCE OF ORDERS:

Acceptance of orders is valid only when so acknowledged in writing by the seller.

SHIPPING:

Unless otherwise agreed at the time the order is placed, seller reserves the right to make partial shipments for whichpayment shall be made in accordance with sellers stated terms. Shipments are made with transportation charges col-lect unless otherwise specified by the buyer. Sellers best judgement will be used in routing, except that buyers routingis used where practicable. The seller is not responsible for selection of most economical or timeliest routing.

CLAIMS:

All claims for damage or loss in transit must be made promptly by the buyer against the carrier. All claims for shortagesmust be made within 30 days after date of shipment of material from the sellers plant.

SPECIFICATION CHANGES OR MODIFICATIONS:

All designs and specifications of sellers products are subject to change without notice provided the changes or modifi-cations do not affect performance.

RETURN MATERIAL:

Product or material may be returned for credit only after written authorization from the seller, as to which seller shallhave sole discretion. In the event of such authorization, credit given shall not exceed 80 percent of the original pur-chase. In no case will Seller authorize return of material more than 90 days after shipment from Sellers plant. Creditfor returned material is issued by the Seller only to the original purchaser.

ORDER CANCELLATION OR ALTERATION:

Cancellation or alteration of acknowledged orders by the buyer will be accepted only on terms that protect the selleragainst loss.

NON WARRANTY REPAIRS AND RETURN WORK:

Consult sellers plant for pricing. Buyer must prepay all transportation charges to sellers plant. Standard shipping pol-icy set forth above shall apply with respect to return shipment from TX RX Systems Inc. to buyer.

DISCLAIMERProduct part numbering in photographs and drawings is accurate at time of printing. Part number labels on TX RXproducts supersede part numbers given within this manual. Information is subject to change without notice.

Bird Technologies Group TX RX Systems Inc.

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Symbols Commonly Used

WARNING

ESD Electrostatic Discharge

Hot Surface

Electrical Shock Hazard

Important Information

CAUTION or ATTENTION

High Voltage

Heavy Lifting


NOTE

Manual Part Number 7-9100

Copyright 2011 TX RX Systems, Inc.First Printing: March 1993

Version Number Version Date

1 03/05/93

2 05/10/93

3 01/24/94

4 07/08/96

5 10/17/11

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Contact Information

Changes to this Manual


Sales Support at 716-217-3113

Customer Service at 716-217-3144

Technical Publications at 716-549-4700 extension 5019

We have made every effort to ensure this manual is accurate. If you discover any

errors, or if you have suggestions for improving this manual, please send your

comments to our Angola, New York facility to the attention of the Technical Publications

Department. This manual may be periodically updated. When inquiring about updates tothis manual refer to the manual part number and revision number on the revision page

following the front cover.

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Table of Contents Manual 7-9100-5 10/17/11

Table of Contents

General Description ........................................................................................... 1

T-Pass Selectivity vs. Cavity Loss.......................................................................4Unpacking ............................................................................................................4

Installation Overview...........................................................................................4Assembly..............................................................................................................4

Peg Rack Assembly ............................................................................................6Cavity / Isolator Mounting ....................................................................................6Installation ...........................................................................................................7

Intermodulation Considerations...........................................................................8Multicoupler Checkout .........................................................................................9

Required Equipment..........................................................................................9Procedure ..........................................................................................................9Measurement Accuracy.....................................................................................9

Multicoupler Tuning ..........................................................................................11

Tuning Specifics ................................................................................................11Fine Cavity Tuning.............................................................................................12Procedure ..........................................................................................................12

Coarse Cavity Tuning........................................................................................13Procedure ..........................................................................................................13Retuning System to all new Frequencies ..........................................................14

Multicoupler Expansion ....................................................................................14Typical Expansion Channel Installation.............................................................14

Peg Rack Procedure .......................................................................................14Relay Rack Procedure.....................................................................................15

Setting Cavity Insertion Loss...........................................................................15Cavity Loss Setting Procedure 1 .....................................................................17

Required Test Equipment..................................................................................17

Procedure for T-Pass Loop ...............................................................................17Procedure for BandPass Loop ..........................................................................19

Cavity Loss Setting Procedure 2 .....................................................................20Required Test Equipment..................................................................................20

Procedure for T-Pass Loop ...............................................................................20Procedure for BandPass Loop ..........................................................................21

Maintenance.......................................................................................................23

Isolators..............................................................................................................23

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Table of Contents Manual 7-9100-5 10/17/11

Figures and Tables

Figure 1: Interconnect diagram of typical system ................................................ 1Figure 2: Typical transmitter noise suppression...................................................3

Figure 3: Front view of 21 channel multicoupler...................................................5Figure 4: Mounting rack detail .............................................................................. 6

Figure 5: Typical combiner installation ................................................................. 7Figure 6: Measuring T-Pass channel performance .............................................. 8

Figure 7: T-Pass cavity fine tuning .....................................................................11Figure 8: T-Pass cavity tuning controls ..............................................................12

Figure 9: Coarse tuning a T-Pass cavity ............................................................13Figure 10: Expansion channel installation..........................................................15Figure 11: Top view of T-Pass cavity .................................................................16

Figure 12: Setting loop adjustment reference.....................................................17Figure 13: Setting T-Pass loop using step attenuators.......................................18

Figure 14: Setting BandPass loop using step attenuators..................................19Figure 15: Setting T-Pass loop insertion loss.....................................................21

Figure 16: Setting Bandpass loop insertion loss ................................................22

Table 1: Specifications..........................................................................................2Table 2: Typical T-Pass channel insertion loss..................................................... 3

Table 3: Test data sheet .....................................................................................10Table 4: Cavity insertion loss reference loop settings.........................................16

APPENDIX A

800 MHz Isolators (Compact Style)

General Description ..........................................................................................24

Installation..........................................................................................................25Verifying Isolator Functionality........................................................................25

Recommended Test Equipment ......................................................................25Measuring Reverse Isolation (S12) ...................................................................25Measuring Insertion Loss (S21).........................................................................25

Figure A1: Verifying Reverse Isolation ...............................................................26Figure A2: Verifying Insertion Loss ....................................................................26Figure A3: Typical Reverse Isolation Waveform ................................................27

Figure A4: Typical Insertion Loss Waveform......................................................27

Table 1: Specifications........................................................................................24

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TX RX Systems Inc. Manual 7-9100-5 10/17/11 Page 1

GENERAL DESCRIPTION

The 73-90-11-NN Series T-Pass Transmit Combin-ers are designed to connect up to 21 transmittersto a common antenna. They use three-port band-

pass filters (called T-Pass cavities) and ferrite iso-lators to provide low channel insertion loss, high

isolation between transmitters, high antenna-to-transmitter isolation, high intermodulation suppres-

sion, and excellent transmitter noise suppression.T-Pass transmit combiners are broadband and

easily adaptable to the most difficult duplex systemdesign requirements.

An interconnect diagram of a typical transmit com-

biner is shown in Figure 1. The T-Pass filter

passes one narrow band of frequencies and atten-uates all others with increasing attenuation aboveand below the pass frequency. The T-Pass filter

has a dual-port output loop plate which allows the

filter to be easily connected to other T-Pass filters.Connections between the filters are made with athru-line cable that behaves like a low loss 50

Ohm transmission line. The thru-line cables areindividually optimized to their own channel fre-quency. No compromises are necessary to accom-

modate other channel frequencies. Each channelcan therefore be anywhere in a very broad fre-

quency range.

An isolator is added at the input to each T-passchannel to increase channel isolation. The ferriteisolators will isolate the transmitter from unwanted

signals that enter the system via the antenna. Thetransmitter sees an excellent impedance match on

its output, because the isolator absorbs reflectedpower that would otherwise enter the transmitters

output stage. This improves the stability, spectralpurity and long-term reliability of the transmitter.

The TX combiners can be expanded one channelat a time with factory-tuned, easy-to-install expan-

sion channel assemblies. Expansion is usuallyaccomplished without modifications to the existing

system, and usually amounts to nothing more thanplacing a new channel assembly, or several, on topof the existing system. New channel frequencies

can be above, below, or between existing channelfrequencies.

The number of channels in the combiner is indi-

cated by the last two digits of the model number inplace of the NN designation. All of the information

for both installation and expansion is included inthis manual. The combiner is easy to install and

S

TX5

TX4

TX3

TX2

TX1

Transmitter Combiner (T-Pass)

Figure 1: Interconnect diagram of a typical Trans-

mit T-Pass Combiner. Typical five channel system

shown as an example.

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Specifications (Note 1) 73-90-11-2C-nn 73-90-11-2D-nn

Frequency Range (Note 2) 806 - 960 MHz

Cavity Type and Diameter 3/4-wave 6.625 (168 mm)

Max Continuous TX Power @ Tx-Tx Separation150 Watts @ 450 KHz

125 watts @ 250 KHz

Isolator Load Power (Continuous) (Note 3) 5W / 60W 5W / 100W

Minimum TX-TX Separation @ Cavity Loss450 KHz @ -1.25 dB

250 KHz @ -1.80 dB

Channel Insertion Loss See Table 2.

Typical TX-TX Isolation @ Minimum Separation -80 dB

Typical Antenna-TX Isolation -70 dB

Typical TX Noise Suppression See Figure 2.

Nominal Input Impedance, Ohms 50

Maximum Input Return Loss (VSWR) -20 dB (1.22:1)

Temperature Range -30 to +60 C

Connectors, Input and Antenna N(F)

Mechanical Mounting Peg Rack included with system

Mounting Options (Notes 4 and 5)-MC: 14 H x 19 W rack-mount adaptor plates

-LR: System supplied without Peg-Rack

Maximum Number of Channels Per Rack 15

Dimensions (Note 6)65.25 H x 24 W x 20.7 D

(1659 x 610 x 526 mm)

Weight, lb. (Kg)Basic single-channel system:

Expansion channel assembly:

31 (14.0)

12 (5.4)

32 (14.5)

13 (5.9)

Notes:

1.-nn in model number represents number of channels.2.Consult factory on T-Pass multicouplers for frequencies below 806 MHz or above 960 MHz.

3.Models available with 5W/25W loads. Same specifications as 60W and 100W models, except load power.4. -MC option reduces maximum number of channels to 12 per pack.

5. -LR systems are tuned and tested on customer frequencies, then disassembled for shipping.6. rack depth with cavity tuning rods at maximum frequency. Rod travel is approximately 2.2 (56 mm).

Table 1: Specifications.

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Tx-to-TX Separation Cavity Loss (dB)Channel Loss (dB) vs. Number of Channels

2 3 4 5 8 10 12

1 MHz

-1.25

-2.1 -2.3 -2.4 -2.5 -2.8 -3.0 -3.3

500 KHz -2.3 -2.8 -3.0 -3.2 -3.6 -3.9 -4.1

450 KHz -2.4 -2.9 -3.2 -3.4 -3.9 -4.1 -4.3

250 KHz -1.80 -3.1 -3.8 -4.1 -4.4 -4.9 -5.2 -5.5

Table 2: Typical T-Pass Channel Insertion Loss.

Note regarding Table 2: The typical channel losses specified here are for equally spaced channelsonly. Channel loss may be higher or lower in multicouplers where separation varies from one channel to

another. Contact TX RX Systems for T-Pass channel loss specifications based on your actual systemfrequency plan.

0

-5

Attenuation(dB)

-10

-15

-20

-30

-25

-35

-40

-45

-50

-55

0.01 0.1 1 10

Offset from Fo (MHz)

100

73-90-11-Series Systems

6.625" Diameter 3/4-Wave, Fo = 860 MHz

IL = -1.25 dB

IL = -1.80 dB

Figure 2: Typical Transmitter Noise Suppression.

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has been factory tuned in most cases so that no

adjustments are necessary. The specifications forthe 73-90-11-NN family of T-Pass combiners arelisted in Table 1 and the typical T-Pass channel

insertion loss is shown in Table 2. The responsecurve shown in Figure 2 shows the typical trans-

mitter noise suppression. Noise suppressiondepends on the cavitys loss setting.

T-Pass Selectivity vs. Cavity Loss

As in the case of bandpass cavity filters, T-Pass fil-ter selectivity depends on the coefficient of cou-pling of the cavity loops at resonance. Tighter

coupling decreases insertion loss and selectivity

while loose coupling increases them.

Although 800 - 1000 MHz T-Pass cavity loops canbe set to approximately -0.8 to -3.0 dB insertion

loss at resonance, TX RX Systems Inc. uses two

standard cavity loss settings, -1.25 and -1.80 dB,that produce adequate selectivity for the majority ofmulticoupler applications in this range. The curves

shown in figure 2 represent the lower selectivityside of the response curve of a typical 6.625 -inchdiameter, 3/4 -wave 860 MHz T-Pass cavity filter.

Bridging loss in a progressive thruline T-Pass

structure varies in the same general manner asbridging loss in a parallel junction bandpass struc-

ture; it decreases as cavity selectivity increases.An optimal cavity loss setting exists that minimizeschannel loss under a specified frequency plan and

number of channels. See Tech-Aid No. 92002 (lit.NO. D3001D93) for a complete set of selectivity

and bridging loss curves for T-Pass cavities from66 to 960 MHz.

UNPACKING

Most T-Pass transmitter multicouplers are shippedfully assembled in a cardboard crate. The cavitiesare usually mounted in a suitably sized Peg-Rack

which is a patented design of TX RX Systems, Inc.Other types of mounting may be supplied for cus-

tom tailored systems as specified at the time oforder. In order to reduce shipping costs, some mul-

ticouplers are shipped partially assembled. In thiscase, customer assembly of the mounting rack andinstallation of the cavity channels may be required.

Accessories or other products ordered with the

multicoupler will usually be found either alreadymounted in the rack or packaged separately as cir-

cumstances dictate. It is important to check thepacking slip against the contents to make sure all

parts are accounted for. Any shortages should be

reported to TX RX Systems or its authorized repre-sentative.

It is important to visually inspect the system com-ponents for any shipping damage as soon as pos-

sible after taking delivery. It is the customersresponsibility to file any necessary damage claims

with the carrier.

The transmit combiner is a very rugged device andis well packaged for damage-free shipping to anyplace in the world. However, a high impact during

shipping can have a detrimental affect. A damaged

shipping container is a sure sign of rough handling.

The most easily damaged parts of the combinerare the tuning rods. These rods are marked wherethey exit from the locking nut with a dab of red var-

nish or other color/type of paint. If this seal appears

to be broken it may indicate that the system hasbeen detuned in transit.

INSTALLATION OVERVIEW

Installation of a TX RX transmitter multicoupler

consists of some or all of the following stepsdepending on how completely the unit was assem-bled at the factory:

1) Determine the exact mounting location for the

multicoupler.

2) Assemble the mounting rack.

3) Install the cavities with isolators then install the

T-Pass Thruline cables and accessories intothe rack.

4) Connect the transmitters and antenna(s) to the

appropriate connectors of the multicoupler.

5) Verify proper operation of each channel by

measuring power output for each individualchannel.

ASSEMBLY

An unassembled multicoupler will usually be bro-ken down into the following general parts groups:

1) Peg rack assembly.

2) T-Pass cavities with mounting clamps.

3) Isolator & loads on mounting brackets withmounting clamps.

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L2

L3

L5

L7

L9

L11

L13

L15

L17

L19

L21

L4

L6

L8

L10

L12

L14

L16

L18

L20

TX 1 TX 2

TX 3

TX 6

TX 7

TX 10

TX 11

TX 14

TX 15

TX 18

TX 19

TX 4

TX 5

TX 8

TX 9

TX 12

TX 13

TX 16

TX 17

TX 20

TX 21

21 Cavity Peg-Rack

Model 93-00-10

Figure 3: Front view of 21 channel multicoupler showing cavity and cable layout. Mul-

ticouplers with fewer channels follow the same cavity stacking and cable pattern from

the bottom up.

Isolator mounting clamp

connector positioned on

bottom of cavity for this

channel only.

Isolator mounting clamp

connector access hole on

bottom for this bracket. Hole

is on top for all other isola-

tors.

Transmitters connect to

type N connector on isola-

tor.

Channel Number

First cavity has built-in short

circuit.

Antenna connects here

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4) T-Pass thruline cables and isolator to cavity

cables.

Peg-Rack Assembly

If the unit was fully assembled then this step maybe disregarded. A separate instruction sheet for

the rack assembly is included with the rack.

Cavity / Isolator MountingAfter the Peg-Rack is assembled, the cavity filters

are mounted. They are packaged separately fromthe isolator assemblies. The cavities have an iden-tification tag attached indicating their frequency

which is used to identify the cavity position in the

system. A T-Pass THRULINE DATA SHEET is

also included in the envelope with this manual foryour multicoupler or expansion channel. This com-puter printout shows the position of each channel

in the multicoupler and indicates its frequency. This

information determines the position of the cavitiesin the rack. This data sheet also shows the positionof critical-length Thruline cables.

Thefront view of a fully assembled 21 channel T-Pass transmit combiner is shown in Figure 3. The

location and assembly order are the same for anysize multicoupler.

1) Mount the cavities for channel 2 (TX 2) on the

right side of the rack starting with pegs 2 and 3.The stainless steel clamps that hold the cavities(part # 8-6212) on the right side should lay in

the peg indentations closest to the vertical rails.(Note that the 8-6212 clamps are also used for

mounting the isolator assemblies.) The clampalways goes around 2 pegs. Orient the cavity as

shown in Figure 4.

2) Identify the isolator assembly for channel 2. The

isolators are labeled with the TX/Channel num-ber and channel frequency. Mount the isolator

assembly to the previously mounted cavityusing two stainless steel clamps. See figures 3

and 4. The clamp connectors for the channel 2isolator assembly should lie on the underside ofthe cavity. An access hole is provided in the iso-

lator mounting plate edge to allow access toone of the hard to get at clamp connectors. It

should face downward.

3) Mount each remaining cavity and isolatorassembly for the right side (channels 3,6,7 etc.)

following the order shown on the T-Passthruline data sheet. The mounting clamps for

these cavities will also lay in the peg indenta-

tions closest to the vertical rails. The isolatormounting clamp connectors and access holeshould be on top for these channels.

4) Similarly mount the cavity and isolator assem-

blies for the channels on the left side of the rackstarting with channel 1 and working up. The

stainless steel clamps that hold the cavities(part # 8-6212) on the left side should lay in the

peg indentations closest to the center of therack. Isolator clamps and access holes are ontop for these channels also.

5) Connect the isolator to the T-Pass cavity as

shown in figure 4, using isolator cable part #3-1918 for each channel. Use pliers with rubberjaws (Utica Part #529-10) to tighten the connec-

tors slightly more than finger tight. DO NOT

OVER TIGHTEN.

Figure 4: T-Pass cavity mounting rack detail.

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6) Similarly connect the T-Pass Thruline cables to

the cavities using the THRULINE DATA Sheetand figure 3 as a guide.

Caution: The Thruline cables mustbe installed in the correct location for

proper operation. Use pliers with rub-ber jaws to tighten these connections

slightly more than finger tight.

This completes the assembly of the basic multicou-plers. Any accessories should be mounted to therack using the supplied mounting hardware and

adapter plates.

InstallationThe multicoupler should be located in a dry andlevel area, indoors. It is best if all transmitters are

as equal in distance as possible from the combin-

ers so that cable losses are the same for all chan-nels. Figure 5 shows a suggested orientation forthe equipment. Two points are important. First, a

work area space should be left as illustrated so thatthe tuning controls are easy to access. This willfacilitate tuning when channel frequencies are

changed. Secondly, space is needed when addingexpansion channels. If there is a lack of space to

access the side of the combiner, then plan to allowthe rack to be moved into the indicated work area

to facilitate adding channels. This will require someslack in the cables that connect to the station trans-mitters.

Four, 17/64" (6mm) diameter mounting holes are

provided in the base for attaching the rack to thefloor using bolts or lag screws.

Each transmitter connects to its respective channelthrough an N-style female connector on the isola-

tor. We recommend using a high quality doubleshield or semi-flexible cable for this purpose. Rigid

cable may be used but extreme care is needed toprevent damage to the connector on the multicou-

pler. High quality connectors should be used for allconnections to the multicoupler. Connectors withgold plated center pins are preferred to minimize

the generation of intermodulation distortion prod-

ucts.

The antenna connection is made to a female Nconnector on the last T-Pass cavity in the chain

near the top of the rack. A flexible jumper of high

quality coax is convenient for this purpose. Thisjumper should be rated to handle the total poweroutput of all the transmitters combined. Since most

transmitter multicouplers exhibit an average 3 dBloss, the actual total power output will be approxi-mately 1/2 the total transmitter power. However,

we recommend cable rated at twice the actualrequired power as a safety factor.

Direct connection to the hard line antenna cable is

also possible but care should be exercised to pre-vent damage to the cavity connector due to exces-sive bending force created by misalignment of the

hard line.

Radio

Cabinet

Radio

Cabinet

Radio

Cabinet

Radio

Cabinet

Work

Area

T-Pass

Transmitter

Combiner

Figure 5: The multicoupler should be positioned so that there is access for tuning and servicing.

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It is advised that the center pin on all mating N

male connectors be checked for proper alignmentbefore connection to the multicoupler. A cockedcenter pin in the male connector can permanently

damage the mating female connector. In manycases, simple field replacement of the damaged

connector is not possible and replacement of anentire subassembly may be required to make the

unit operational.

This system is designed for use with separatetransmit and receive antennas. For best operation,the transmit and receive antennas should be sepa-

rated vertically by 20 feet with little or no horizontal

offset between antennas. Lesser separations can

be used but with an increased risk of harmful inter-ference between radio systems. In most cases, it

will be desirable to mount the receive antenna

higher than the transmit antenna to maximize thetalk-back range of low power portable radios.

Intermodulation ConsiderationsFollowing the previously mentioned antenna spac-

ing recommendations will go a long way towardminimizing or eliminating intermodulation (IM)

interference. IM is the result of a frequency mixingprocess that occurs when two or more RF signals

are present simultaneously in the same circuitrywhere nonlinearity occurs. Product frequenciesgenerated have frequencies that are determined by

relatively simple mathematical relationships such

as F(im) = 2F1-F2 and are normally determined by

doing a computer intermodulation analysis for theantenna site. These products can be generated in

UG27 Elbow Connector

& UG57 Male-MaleAdaptor

UG57

Male-Male

Transmitter

Transmitter

Transmitter

Singleor Dual

Section

Isolators

Single

or Dual

Section

Isolators

Single

or Dual

Section

Isolators

T-PassCavity Filter

Channel 3

Channel 2

Channel 1

Wattmeter 2

50 Ohm

Load

Wattmeter 1

This T-Pass Loop

requires a 3-1268

short circuitconnector

Figure 6: Equipment hookup for measuring T-Pass channel performance.

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a corroded tower joint, metal-roofing, transmitter

final amplifier or the receiver front-end.

Both cavity filters and ferrite isolators isolate the

transmitters connected to the combiner from one-another thus reducing intermodulation interference.

However in all transmitter combiners, intermodula-tion products are reduced in strength but never

completely eliminated. They have to be reduced byan amount to meet the Federal Communications

Commission, 43 + 10 Log(Power Out) rule for spu-rious output reduction. Because of the limitationsimposed by the tension and friction joints in con-

nectors, IM products will be down 100 to 120 dB

below carrier so they are still strong enough to

cause problems if they fall on a near-by receiverfrequency.

To avoid transmitter generated IM problems, do

not put two channels on the same combiner thatyour IM software predicts will cause interference bygenerating either 3rd or 5th order IM products.

Having at least two transmitter combiners allowsmaximum flexibility in dealing with transmitter gen-erated IM.

Multicoupler Checkout

Fully assembled multicouplers are factory tunedand ready for routine operation after properly con-

necting the transmitters and antenna(s) as outlinedpreviously. The components used in systems thatrequire partial assembly have been fully interca-

bled and tuned so they will not require tuning. How-ever, it is recommended that the performance of

the multicoupler be checked initially and datarecorded for future reference. This is done by mea-

suring the input and output power of each channeland recording the data. Figure 6 shows the equip-ment hook up.

REQUIRED EQUIPMENT

If a power monitoring system is not installed alongwith the multicoupler, two Bird Model 43 thruline

wattmeters or equivalent can be used. They shouldbe equipped with elements for the frequency bandof interest and rated for the expected transmitter

power output. The use of two wattmeters elimi-nates errors that can occur from changing cable

lengths. The measurements should only be doneone channel at a time because most wattmeters

cannot accurately measure the total power of twoor more transmitters simultaneously. A pocket cal-

culator with Log functions makes for easy calcula-tion of power loss in dB using this measured data.

PROCEDURE

Start with channel 1 at the bottom of the rack andproceed to the next higher channels. The two watt-meters should be connected to the equipment as

shown in figure 6. Note that the use of the elbowand/or male-male connectors allows the shortest

connections and negligible hook up loss. Longercable lengths will tend to increase measurement

error.

It is important that the same wattmeters and watt-meter elements be used in the same positionthroughout the tests. The serial numbers of the

wattmeters should be recorded for future refer-

ence. Wattmeter elements may not have serial

numbers so they need to be labeled or otherwisekeyed to a specific wattmeter to assure repeatabil-ity of the measurements.

A convenient data sheet is included in Table 3 andmay be photo copied. After entering the data andcalculating the power losses, it should be retained

for future reference. A column is provided for enter-ing the factory measured loss from the T-PassThruline Data sheet that was included in the enve-

lope with this manual. The factory data wasobtained with a laboratory network analyzer having

an accuracy 0.05dB. The readings obtained usingthe wattmeter method outlined may vary consider-

ably from the factory values and this difference isexplained in the next paragraph.

MEASUREMENT ACCURACYThe Bird thruline wattmeter has a measurement

accuracy of +/- 5% of full scale. When using a 100watt element in this meter, the measurement error

can be as great as + or - 5 watts.

As an example of the actual dB loss readings that

might be produced using the wattmeter method,consider a T-Pass channel that has a factory mea-

sured loss of 3.0 dB. We would expect that a 100watt transmitter would produce 50 watts out of this

channel but the actual wattmeter reading for theinput power could measure as low as 95 watts toas high as 105 watts. The measured output power

could run from 45 to 55 watts. It is possible that theoutput reading may be 5 watts low while the input

reading is 5 watts high or just the opposite. Thesetwo extremes would yield the following dB loss val-

ues:

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For a Power Out (PO) of 45 watts and a Power

Input (PI) of 105 watts:

Loss (dB) = 10 Log10 (45/105)

Loss (dB) = -3.7

For a PO of 55 watts and PI of 95 watts:

Loss (dB) = 10 Log10(55/95)

Loss (dB) = -2.4

So the calculated loss for this channel can run from

-2.4 to -3.7dB and be acceptable considering themeasurement error factor. The actual error couldbe much greater if a 250 watt element was used;

the measured values could vary by as much as +/-12.5 watts. So using a wattmeter element with the

smallest possible rating is important for accuracy.Use of between series adapters or UHF type con-

nectors for making connections to the wattmeters,device under test or loads, could make this error

even worse due to the additional impedance mis-match that these connectors can cause.

Transmitter Combiner Test Data Sheet

Combiner Model Number:

Serial / Job Number:

Date: Technician:

Wattmeter #1 Serial Number:

Wattmeter #2 Serial Number:

Channel

Number

Power Input

(Pi) in Watts

Power Output

(Po) in Watts

Power Ratio

Po / Pi

Calculated

Loss (dB)

Factory Measured

Loss (dB)

1

2

34

5

6

7

8

9

10

11

12

13

14

15

Table 3: Test Data Sheet.

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MULTICOUPLER TUNING

T-Pass transmitter combiners are pre-tuned at thefactory and usually require no adjustment. T-Passexpansion channels are also pretuned but may

require fine tuning after being installed in an exist-ing system. Channels that are close in frequency

(adjacent channels in the multicoupler) to theexpansion channel may also benefit from fine tun-

ing due to the slight interaction that occurs with thenew channel. The procedures that follow may beused at any time to verify that any or all channels

are properly tuned or to correct any misalignments.

It is interesting to note that T-Pass filters, bandpassfilters and cavity filters in general can act as imped-

ance transformers as well as filters. It is for thisreason that many field service personnel claim thatthey can always tune a filter better than the factory.

What isn't generally realized is that their tuning

efforts are usually producing better impedancematching between transmitter and antenna whichcan be improved by the transforming action of fil-

ters. Since the filters are usually tuned using labo-ratory grade 50 ohm loads, the tuning adjustment

that produces this improved match will be slightly

different than the factory adjustment. While thistuning may produce slightly greater power outputreadings, it will rarely produce any discernible

change in system performance.

It is our recommendation that channel tuning onlybe attempted under the previously mentioned con-

ditions or when it is suspected that the combinerhas been tampered with or subjected to extreme

shock in shipping or installation. This condition isindicated when the channel loss is in excess of thatexpected from actual measurement of power input

and output.

Tuning SpecificsTuning the multicoupler consists of tuning the indi-vidual T-Pass channels. T-Pass channel tuning

involves cavity filter tuning. For multicoupler mod-

els used at 800 MHz and above, isolator tuning isnever required because these isolators are fixed-tuned at the factory for specific frequency bands

and have no user adjustments.

Transmitter

Output

Section

Termination

Two Single Section

or One Dual Isolators

T-Pass

Cavity Filter

Wattmeter

To Other

Channels

To Other

Channels

Input

50 Ohm

Termination

Fine

Tuning

Output

Coarse

Tuning

Figure 7: Using a Wattmeter for T-Pass cavity fine tuning.

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Fine Cavity Tuning

Figure 7 shows a hookup suitable for fine tuningany channel under power while installed in the mul-ticoupler. The term fine tuning here refers to cavi-

ties that have already been tuned to frequency andmay only require adjustment of the fine tuning con-

trol (+/- 50 KHz). The transmitter is used as a sig-nal source and the cavity is adjusted for minimum

reflected power.

Procedure

With the transmitter keyed, the cavity fine tuningcontrol is adjusted (pushed in or out) to obtain a

minimum meter reading. See Figure 8 for a detail

of the cavity tuning controls. If a minimum meter

reading is obtained with the fine tuning rod fully inor completely out, do the following:

1) Set the fine tuning rod so that about 1/2 its

length is inserted into the cavity.

When tuning a cavity that has been in

service for some time it is not unusualto find the main tuning rod hard tomove in or out. This occurs because

TX RX uses t echniques borrowedfrom microwave technology to provide large area

contact surfaces on our tuning plungers. These sil-ver plated surfaces actually form a pressure weld

that maintains excellent conductivity. This pressureweld develops over time and must be broken tomove the main tuning rod. This is easily accom-

plished by gently tapping the tuning rod with a plas-

tic screwdriver handle or small hammer so that itmoves into the cavity. The weld will be broken withno damage to the cavity.

When adjusting the coarse tuning rod, it is easy to

put the cavity far off resonance and cause most ofthe transmitter power to be reflected back into the

isolator output section load. This load should becapable of dissipating this power or damage could

result. If in doubt about the loads capability, followthe coarse tuning procedure outlined below. It isbased on the use of a spectrum analyzer and fre-

quency generator which avoids the need to con-

sider power levels.

2) Loosen the coarse tuning rod locking screw (5/32"/4mm Allen/HexKey wrench required) and

move the rod in or out slightly to obtain mini-

mum meter reading. Small movements of thecoarse tuning rod are facilitated by tapping therod with the handle end of a screw driver while

gently pushing or pulling the main tuning rod.Tighten the coarse tuning locking screw.

3) Adjust the fine tuning control for a minimummeter reading.

4) Tighten the fine tuning locking mechanism.

NOTE

Cavity Resonator

Coarse Tuning Rod

Coarse Tuning Lock10-32 Cap Screw

Calibration Index

Input/Output Port

Loop Plate Assembly

Loop PlateHold Down Screws

Loop Plate Assembly

Input/Output Port

Calibration Mark

Calibration Index

Fine Tuning Rod

Fine Tuning LockKnurled Thumb Nut

Figure 8: T-Pass cavity tuning controls.

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Coarse Cavity Tuning

When a T-Pass cavity frequency has to bechanged by over 50 KHz, adjustment of the maintuning rod is required. Large frequency changes

are more easily observed when using a trackinggenerator and a return loss bridge to give a swept

display of the return loss curve. The return losscurve is a very precise indicator of T-Pass cavity

tuning. The test equipment hookup for doing this isillustrated in Figure 9 and uses the following equip-

ment;

1) Spectrum Analyzer that covers the frequencies

of interest such as the Bird Technologies Sig-

nal Hawk .

2) Signal generator capable of producing the fre-quencies of interest.

3) Eagle Return Loss Bridge (35 dB directivity).Model RLB150N3A.

4) Double shielded coaxial cable test leads(RG142 B\U or RG223/U).

5) 50 Ohm load with at least -35 dB return loss(1.10:1 VSWR).

6) Shorting stub from holder at top of T-Pass rack

(Part # 3-1268).

Procedure

1) Set the spectrum analyzer for the desired chan-nel frequency (display center) and vertical scale

of 10 dB/div. Set the signal generator for thedesired center frequency.

2) Connect the return loss bridge to spectrum ana-lyzer and signal generator as shown in figure 9

but do not connect it to the cavity. Leave thetest port (called the load port) on the bridge

open.

3) Set up the 0 dB return loss reference displayon the spectrum analyzer. Then connect thereturn loss bridge.

4) Loosen the fine tuning rod locking nut and set

the fine tuning rod so that 1/2 its length isinserted into the cavity.

5) Loosen the main tuning locking screw and

move the main tuning rod in or out to obtainmaximum return loss at the desired frequency.

LOAD

Spectrum Analyzer

Bird SignalHawk

Signal Generator

RLB - 150 Bridge

50 Ohm Load

T-Pass

Cavity Filter

3-1268

Short Circuit

Connector

Figure 9: Equipment hookup for

T-Pass cavity coarse tuning.

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Small movements of the main tuning rod are

facilitated by tapping the rod with the handleend of a screw driver while gently pushing orpulling the main tuning rod.

6) Lock the Main and Fine tuning rods and reinstall

the cavity in the system. Use the previously out-lined fine tuning procedure to verify proper tun-

ing under power.

Retuning System To All New Frequencies

When retuning the combiner to all new frequenciesperform the following procedure in a step-by-step

fashion;

1) Determine new thruline cable lengths for thenew channels and the specific stacking order inthe rack. TX RX Systems Sales engineers will

assist by making the calculations using their

design software. Due to variations in coaxialcable characteristics and assembly techniques,factory supplied cables are recommended.

2) Use the Coarse Tuning procedure as outlinedearlier in this manual to tune each cavity chan-

nel to the new transmitter frequencies.

3) Connect the channels according to the newThru-line cable chart.

4) Fine tune each channel using the fine tuningprocedure as outlined earlier in this manual,

starting with channel 1 and proceeding to thenext higher channel. After tuning all channels,

repeat this step a second time to verify thatthere is no more channel interaction.

5) Verify channel losses if desired using the multi-coupler checkout procedure outlined previously.

MULTICOUPLER EXPANSION

Expansion channels for your multicoupler may beordered directly from TX RX Systems or its autho-

rized representative. The systems engineer willhelp you select the right model and any required

options.

The expansion channel and options are shipped

with mounting instructions and a new T-PassThruline cable sheet which shows the exact mount-

ing location of the new channel in the existing sys-tem. In most cases, this channel will be added

directly to the next topmost position in the rack andthe antenna connection will then move to this cav-

ity. A new thruline cable will connect this channel

to the existing cavities.

The system engineer may also advise that the cav-

ity insertion loss on some of the existing channelsneeds to be changed in order to accommodate a

new channel. This can be necessary when the newchannel is much closer in frequency separation to

existing channels than that previously encoun-tered. This usually means increasing the cavity

loss for all close spaced channels which providesthe increased selectivity required. Cavity insertionloss values are shown on the T-Pass Thruline

cable sheet.

Typical Expansion Channel InstallationThe following text is a procedure for adding expan-sion channel components to a typical T-Pass

Transmitter Multicoupler. Please keep in mind that

instructions shipped with the expansion compo-nents supersede these procedures.

Typical Parts Included(Quantity and Description)

(1) T-Pass Cavity Assembly.

(1) Single/Dual Isolator w/load on Mounting Plate

(1) 9.4" Isolator to Cavity Interconnect Cable

(4) Stainless Steel Band Clamps

(1) T-pass Thru-line Cable

(1) T-pass Thruline Chart.

PEG RACK PROCEDURE1) Determine the location of the Expansion Chan-

nel in the rack by consulting the newTHRULINE cable chart.

2) Mount the cavity in the peg rack using two (2)

stainless band clamps, refer to Figure 10.

3) Rotate the cavity body so that the connectors

are orientated the same as those on the othercavities and that no cavity-end cap screws are

preventing a flush fit with a mounting peg.

4) Tighten the cavity mounting clamps.

5) Attach the isolator mounting plate to the cavityusing two (2) band clamps. Clamp screws

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should be positioned as shown in figure 10. Do

not tighten the clamps.

6) Rotate the isolator mounting bracket so that the

isolator is in the vertical plane as illustrated,forming a smooth line in relation to the other

channels in the rack.

7) Due to the limited space, tightening may requirethe use of a 5/16" open end wrench. Tighten

both clamps securely.

8) Connect the isolator-to-cavity cable. Use a pair

of cable pliers to tighten-up the connectors.

9) Connect the new channel to the multicouplerusing the proper length T-Pass Thruline cable.Use a cable pliers to tighten these connections.

The required length thruline cable andnew cabling chart has either been fac-tory supplied or is to be determined

and fabricated by the customer asdetermined at the time of order. UseT-Pass THRULINE d esign sheet s

supplied by the factory.

10) If necessary, reset cavity insertion loss of adja-cent channels as noted on the Thru-line cable

sheet. Follow the procedure outlined underSetting Cavity Insertion Loss.

11) Fine tune the T-Pass cavity of the expansionchannel according to the procedure outlined

earlier.

RELAY RACK PROCEDURE

Because of their width, 6.625 cavitiesare mounted on relay racks in a hori-zontal orientation on cavity deck

plates.

1) Determine the location of the expansion chan-nel in the rack by consulting the new

THRULINE cable chart.

2) If necessary install an empty cavity deck in therack using 4 Phillips screws. If there is room onan already existing cavity deck then skip this

step of the procedure.

3) Mount the cavity on the deck by laying the cav-ity onto the V shaped cavity bracket.

4) Rotate the cavity body so that the connectors

are oriented the same as those on the othercavities in the system. Secure the new cavity tothe brackets using (2) stainless band clamps.

5) Tighten the cavity mounting band clamps.

6) Connect the black isolator-to-cavity cable usinga pair of cable pliers to tighten-up the connec-

tors.

7) Connect the new channel to the combiner usingthe proper length T-Pass Thruline cable. Use apair of cable pliers to tighten these connections.

The required length Thruline cable

and new cabling chart has either beenfactory supplied or is to be deter-

mined and fabricated by the customeras determined at the time of order.Use T-Pass Thruline design sheets

supplied by the factory.

8) If necessary, reset the cavity insertion loss ofthe adjacent cavities as noted in the Thruline

cable sheet. Follow the procedure outlinedbelow under Setting Cavity Insertion Loss,

9) Fine tune the T-Pass cavity of the expansionchannel according to the fine tuning procedure

outlined earlier.

SETTING CAVITY INSERTION LOSS

It is sometimes necessary to reset the insertion

loss of a T-Pass cavity filter in order to change itsselectivity. Increasing the loss will increase the

NOTE

NOTE

NOTE

Figure 10: Expansion channel installation.

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cavity selectivity which may be necessary to

accommodate more closely spaced channels.

Changing the loss is accomplished by rotating the

coupling loops to change the coefficient of cou-pling. Both loops are normally adjusted for a given

insertion loss setting. Most T-Pass cavities have aCalibration Index label beside both loops that gives

a relative indication of their settings (see Figure11). In actual practice, these marks are not accu-

rate enough for setting loss values consistently.

Two procedures are offered for setting the cavity

loss. Both procedures take advantage of the factthat when a tee connector is placed on a singlebandpass or T-Pass loop, a rejection notch can be

observed across the tee. The depth of the rejectionnotch is directly related to the loop's coefficient of

coupling.

The first procedure uses precision rotary attenua-tors, a signal generator and an RF millivolt meter to

provide very accurate results. The actual loss set-ting obtained when this procedure is carefully fol-lowed will be within one tenth of a dB of the desired

value and the return loss will be 20 dB (1.25:1) or

better.

The second procedure uses a spectrum analyzerand frequency generator and produces slightly less

accurate results. When this procedure is carefully

followed, the loss settings will be within two tenthsof a dB of the desired value and the return loss willusually be -15 dB (1.5:1 VSWR) or better. The

advantage of this procedure is that it is much fasterto do, does not require precision attenuators andwill yield acceptable results in most cases.

Table 4 shows a reference chart for setting T-Pass

cavity loss with either procedure. The chart showsthe desired cavity loss settings and the reference

setting for both the T-Pass and bandpass loopassembly. The reference notch depth for a givenloss is that which can be observed across a tee

connector connected to either loop assembly. Notethat the reference notch depths are slightly differ-

ent when the T-Pass loop assembly has a built-in

Calibration

Mark

Bandpass

Loop

T-Pass

Loop

Loop Locking

Screws (6 places)

Figure 11: Top view of T-Pass cavity.

Cavity Loss (dB)Built-in Short

CircuitCoupling Loop Type

TX RX Systems

Part Number

Reference Notch

Depth (dB)

1.25 NoT-Pass

Bandpass

3-3721

3-2294

-9

-17

1.25 YesT-Pass

Bandpass

3-2292

3-2294

-9.6

-16.7

1.80 NoT-Pass

Bandpass

3-3721

3-2294

-6.6

-14.6

1.80 YesT-Pass

Bandpass

3-2292

3-2294

-7.2

-13.9

Table 4: Cavity insertion loss reference loop settings.

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short circuit. This loop is only used once in the bot-

tom cavity of the T-Pass stack. Detailed proce-dures and illustrations follow on the next fewpages.

CAVITY LOSS SETTING PROCEDURE 1

This procedure uses precision rotary attenuators, asignal generator and an RF Millivolt meter.

Required Test Equipment1) Signal generator capable of producing a CW

signal level of at least -10 dBm with variableoutput level capability at the frequency of inter-

est.

2) An RF voltmeter with a 0.001 Volt (-50 dBm)scale and a 50 Ohm input adapter. HelperInstruments RF millivolter used for this exam-

ple.

3) Rotary Attenuators, 1@ 0-1 dB in 0.1 dB incre-ments. 1@ 0-10 dB in 1.0 dB increments. 1@

0-70 dB in 10 dB increments. JFW Industriesmodel 50BR-017.

4) Two 10 dB fixed attenuator pads with BNC con-nectors. JFW Industries model 50F-010.

5) UG-914/U, BNC(F)-BNC(F), union. TX RX Sys-

tems' part # 8-5805.

6) UG-28A/U, N(F), N(F), N(F) tee.

7) UG-57B/U, N(M)-N(M) coupling.

8) Two, UG-201A/U BNC(F)-N(M) adapter. TX RX

Systems' part # 8-5814.

9) 50 ohm coaxial cable test leads with BNC maleconnectors (high quality cable).

A spectrum analyzer may be used in place of the

RF voltmeter. However, the personnel doing the

work should fully understand the procedure andunderstand the use of the analyzer for this applica-tion. We have found it convenient to use test

cables with BNC connectors. They allow for more

convenient connection to test equipment and tosmall attenuator pads. UG-201 BNC to N adaptersare used when connections to N connectors are

needed.

Procedure for T-Pass Loop

1) Set the signal generator for the desired operat-ing frequency (within 1 MHz of operating fre-

quency) and for an output signal level ofapproximately -10 dBm. Set the rotary attenua-

ZEROSET ZERO

SET

00000000

1 23

3 4 56 7 8 9 10

Modulated

Signal Source RF Voltmeter

Rotary Attenuators

Set to Loop Reference Settings

0.1 dB/Div. 1.0 dB/Div. 10 dB/Div.

All cables are 50 Ohm

coaxial. Double shielded

cables preferred.

UG914/UFemale-Female

Connector

10 dB Attenuator Pads

50 Ohm Adaptor

Figure 12: Setting loop adjustment reference level.

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tors for the Reference Notch Depth Value

shown in the chart (table 4) for the desiredinsertion loss and T-Pass loop part #.

2) Connect the test leads together through thefemale union, as shown in Figure 12, and

adjust the range switch and the zero set on thevoltmeter for a convenient reference level (A

level of 2 on the 0 to 3 scale for example) on themeter. The generator output level may also be

adjusted slightly if necessary.

3) Remove the bandpass loop from the cavity and

insert it, connector end first, back into the cavity

and tighten all 3 screws securely. See Figure

13.

4) Set all three attenuators for 0 dB but leave them

in the circuit.

5) Connect a UG-28A/U Tee connector and UG-

57B/U coupling to the T-Pass loop as shown infigure 13. Then connect the test leads asshown. Make sure to install the short circuitstub

(part # 3-2330) from the top of the T-Pass rackif the loop does not have an internal short.

6) Loosen the main tuning rod locking screw and

slowly slide the tuning rod in or out to obtain adip (minimum voltage) in the meter reading

which indicates cavity resonance. Use the finetuning control to maximize the dip (the fine tun-ing rod should not be full in or out which would

indicate that slight adjustment of the main tun-

ing rod is necessary). Note the meter reading.

7) If the meter reading is greater or less than thereference level from step 3, the T-Pass loop

rotation will have to be adjusted. If the meter

Modulated


Rotary Attenuators



50 Ohm Adaptor

UG-28A/U

UG-57B/U

T-Pass

Loop

10 dB Pad 10 dB Pad

Short Circuit Connector

3-1268 from top of rack

Bandpass Loop turned upside down

with connector inserted into cavity.

Loop visible and screws tight.

Figure 13: Setting the T-Pass loop using step attenuators.

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reading is greater than the reference level, the

loop will have to be rotated so that the calibra-tion mark on the loop points to a slightly highernumber on the calibration index label. Con-

versely, if the meter reading is less than the ref-erence, the loop will have to be rotated so that

the index mark points to a slightly lower numberon the calibration index. Loosen the three loop

locking screws and rotate the loop so that theindex mark is moved to the next higher or lower

calibration tag number as needed and tightenthe 3 locking screws. Note that tight screws arenecessary for accuracy.

8) Repeat steps 6 and 7 until the minimum meter

reading is equal to the reference level from step3. Rotation of loops will change the cavity fre-quency slightly.

9) The Bandpass loop should be installed with the

connector up and the ground point circle ori-ented toward the center of the cavity as shownin Figure 14.

10) Remove the short circuit stub from the T-Pass

loop.

Procedure for Bandpass Loop1) Maintain the previous signal generator settings

and set the rotary attenuators for the proper set-ting as shown in table 4 for the Bandpass Loop.

2) Connect the test leads together through thefemale union and adjust the range switch and

the zero set on the voltmeter for a referencelevel (A level of 2 on the 0 to 3 scale is conve-

nient) on the meter. See figure 12. The genera-

Modulated


Rotary Attenuators



50 Ohm Adaptor

UG-28A/U

UG-57B/U

BandpassLoop

10 dB Pad 10 dB Pad

Previously calibrated T-Pass Loop 3-1268

short circuit removed.

Small Circle on Bandpass Loop indicates

ground end of loop and should be

oriented as shown.

Figure 14: Setting the Bandpass loop using step attenuators.

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tor output level may also be adjusted slightly if

convenient.

3) Set all three attenuators for 0 dB but leave them

in the circuit.

4) Connect a UG-107 Tee and the UG-57B/U tothe Bandpass loop as shown on figure 14. Then

connect the test leads as shown. Make sure theshort circuit stub has been removed from the T-

Pass loop.

5) Loosen the main tuning rod locking screw (see

figure 8) and slowly slide tuning rod in or out to

obtain a dip (minimum voltage) in the meter

reading which indicates cavity resonance. Usethe fine tuning control to maximize the dip (thefine tuning rod should not be full in or out which

would indicate that slight adjustment of the

main tuning is necessary). Note the meter read-ing.

6) If the meter reading is greater or less than thereference level from step 2, the bandpass looprotation will have to be adjusted. If the meter

reading is greater than the reference level, theloop will have to be rotated so that the calibra-

tion mark on the loop, points to a slightly highernumber on the calibration index label. Con-

versely, if the meter reading is less than the ref-erence, the loop will have to be rotated so thatthe index mark points to a slightly lower number

on the calibration index. Loosen the three looplocking screws and rotate the loop so that the

index mark is moved to the next higher or lowercalibration tag number as needed and tighten

the 3 locking screws. Note that tight screws arenecessary for accuracy.

7) Repeat steps 5 and 6 until the minimum meterreading is equal to the reference level from step

3. Rotation of loops will change the cavity fre-quency slightly.

8) Make sure that all the loop locking screws aretight. The cavity loops are now set and the cav-

ity should now be tuned to the desired fre-quency as outlined elsewhere in this manual.

CAVITY LOSS SETTING PROCEDURE 2

This procedure uses a spectrum analyzer, signalgenerator, and fixed attenuator pads.

Required Test Equipment

1) Spectrum Analyzer and a signal generator.

2) Two 10 dB fixed attenuator pads with BNC

connectors. JFW Industries model 50F-010.

3) UG-914/U, BNC(F)-BNC(F), union. TX RX Sys-tems' part # 8-5805.

4) UG-28A/U, N(F), N(F), N(F) tee.

5) UG-57B/U, N(M)-N(M) coupling.

6) Two, UG-201A/U BNC(F)-N(M) adapter. TX RX

Systems' part # 8-5814.

7) 50 ohm coaxial cable test leads with BNC maleconnectors (high quality cable).

We have found it convenient to use test cables withBNC connectors. They allow for a more convenientconnection to test equipment and small attenuator

pads. UG-201 BNC to N adapters are used whenconnections to N connectors are needed.

Procedure for T-Pass Loop1) Remove the screws that hold in the bandpass

loop assembly; remove the assembly; invert itand place it back into the cavity. The coupling

loop will be visible. Install and tighten the threelocking screws.

2) Connect the test leads to the spectrum ana-lyzer; turn it on and let it warm up for at least 30

minutes.

3) Connect the 10 dB attenuator pads to the testleads. They will remain connected for all subse-quent measurements.

4) Note the Reference Notch Depth value for the

T-Pass loop assembly to be adjusted from thechart, see table 4.

5) Set the spectrum analyzer for the frequency ofthe channel of interest (within 5 MHz of actual

operating frequency)

6) If the Reference Notch Depth is 8 dB or lessthen set the display for a vertical range of 2dB/

div otherwise set it for 10dB/div.

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7) Temporarily connect the test leads from the

spectrum analyzer together through a UG-914BNC union to set the zero reference.

8) Connect a UG-28 tee and a UG-57 coupling tothe T-Pass loop as shown in Figure 15.

9) Connect the test leads from the spectrum ana-

lyzer to the tee connector as shown in figure 15.

10) Adjust the cavities main tuning rod so that a

rejection notch appears in the center of the dis-play.

11) Loosen the three loop locking screws and

rotate the loop to obtain the reference notchdepth from step 4.

The tightness of the locking screws

affects the depth of the rejectionnotch slightly. It is usually necessary

to rotate the loop for a notch depththat is slightly less than the reference.The Notch depth will tend to increase

slightly as all three locking screws aretightened.

12) Remove the bandpass loop and place it back

into the cavity with the connector-end up.

Procedure for Bandpass loop

1) The Bandpass loop should be installed with theconnector up and the ground point circle ori-

ented toward the center of the cavity as shownin Figure 16.

2) Connect the test leads, with 10 dB pads

attached, to the spectrum analyzer; turn it on

NOTE

UG-28A/U

UG-57B/U

T-Pass

Loop

10 dB Pad10 dB Pad

Short Circuit

Connector 3-1268

from top of rack

Bandpass Loop

turned upside down

with connector

inserted into cavity.

Loop visible and

screws tight.

Spectrum Analyzer

Bird SignalHawk

Signal Generator

Figure 15: Setting a T-Pass loop for a specific cavity insertion loss.

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and let it warm up for at least 30 minutes if thishas not been done.

3) Note the Reference Notch Depth value for the

Bandpass loop assembly to be adjusted fromtable 4.

4) Set the spectrum analyzer for the frequency ofthe channel of interest (within 5 MHz of actual

operating frequency).

5) If the Reference Notch Depth is 8 dB or less

then set the display for a vertical range of 2dB/div otherwise set it for 10dB/div.

6) Temporarily connect the test leads from the

spectrum analyzer together through a UG-914BNC union to set the zero reference. Make sure

to use the 10 dB pads which should remain onthe test cables for all measurements.

7) Connect a UG-28 tee and a UG-57 coupling tothe bandpass loop as shown in figure 16.

8) Connect the test leads from the spectrum ana-

lyzer to the tee connector as shown in figure 16.

9) Adjust the cavities main tuning rod so that a

rejection notch appears in the center of the dis-play.

10) Loosen the three loop locking screws and

rotate the loop assembly to obtain the refer-

ence notch depth from step 3.

The tightness of the locking screwsaffects the depth of the rejection

notch slightly, it is usually necessaryto rotate the loop for a notch depth

that is slightly less than the reference.The Notch depth will tend to increase slightly as allthree locking screws are tightened.

NOTE

10 dB Pad 10 dB Pad

UG-28A/U

UG-57B/U

Bandpass

Loop

Previously calibrated

T-Pass Loop 3-1268

short circuit removed

Small Circle on

Bandpass Loop

indicates ground

end of loop and

should be oriented

as shown.

Spectrum Analyzer

Bird SignalHawk

Signal Generator

Figure 16: Setting a Bandpass loop for a specific cavity insertion loss.

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11) Tighten all loop locking screws. The cavity lossis now set. The cavity will have to be tuned to

its operating frequency following the proce-dures outlined earlier in this manual.

MAINTENANCE

Because T-Pass transmitter multicouplers arecomposed of mostly passive components, they willcontinue to operate without any maintenance for

years and there is no recommended maintenanceperiod. We do feel, however, that it is wise to check

multicoupler performance by measuring channelloss periodically and this may be done at any con-venient time along with other radio system mainte-

nance.ISOLATORS

Isolators perform two important functions. Their pri-mary function is to keep unwanted RF frequencies

out of the transmitter so that intermodulation prod-

ucts cannot be generated. Isolators have a sub-stantial amount of reverse isolation. They also

ensure that the transmitter never sees any signifi-cant reflected power so it will always operate with

maximum stability at full-power output. Isolatorsprevent energy from getting into the transmitters

output by dumping any RF energy entering the out-put of the isolator into a dummy load. The model73-90-11 series of T-pass transmit combiners will

use either single section or dual section isolators atthe input to each T-pass channel.

Single-section isolators have one load port. A prop-

erly sized load capable of dissipating the maximumexpected reflected power that might be encoun-tered should be used. Dual section isolators have

two load ports, one for each section. Althoughloads of equal power rating may be used for both

ports, it is customary to use an output load capableof dissipating the maximum expected reflected

power that might be encountered. A small load (5watts) is usually factory installed on the first sectionof the isolator where high reflected power is not a

factor. Refer to Appendix A for a further discus-sion of isolators.

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GENERAL DESCRIPTION

Isolators perform two important functions. Their pri-mary function is to keep other RF frequencies outof the transmitter so that intermodulation products

cannot be generated. Isolators have a substantialamount of reverse isolation. They also insure that

the transmitter never sees any significant reflectedpower so it will always operate with maximum sta-

bility at full-power output. Isolators prevent energyfrom getting into the transmitters output stage by

dumping reflected RF energy entering the output ofthe isolator into a dummy load.

The 800 MHz (compact style) isolators available

from TXRX Systems are broad-band and do not

require tuning. The isolators are available as eithersingle section or dual section models. Dual section

models consist of two single sections mounted inthe same case with a load permanently attached to

the load port of the first section. Table A1 lists the800 MHz isolators available from TX RX Systems

along with their performance specifications.

Appendix A

800 MHz Isolators (Compact Style)

TXRXSystems

Part #

FreqRange

(MHz)

Isolation(dB)

(min)

InsertionLoss

(dB) (max)

3-22223P 764 - 776 50 0.50

3-22224P 794 - 806 50 0.50

3-22225P 806 - 824 50 0.50

3-22226P 851 - 869 50 0.50

3-22227P 870 - 894 50 0.50

3-22228P 925 - 935 50 0.50

3-22229P 935 - 940 50 0.50

3-22230P 940 - 960 50 0.50

3-22223PL 764 - 776 50 0.50

3-22224PL 794 - 806 50 0.50

3-22225PL 806 - 824 50 0.50

3-22226PL 851 - 869 50 0.50

3-22227PL 870 - 894 50 0.50

3-22228PL 925 - 935 50 0.50

3-22229PL 935 - 940 50 0.50

3-22230PL 940 - 960 50 0.50

TXRXSystems

Part #

FreqRange

(MHz)

Isolation(dB)

(min)

InsertionLoss

(dB) (max)

3-22223PLA 764 - 776 50 0.50

3-22224PLA 794 - 806 50 0.50

3-22225PLA 806 - 824 50 0.50

3-22226PLA 851 - 869 50 0.50

3-22227PLA 870 - 894 50 0.50

3-22228PLA 925 - 935 50 0.50

3-22229PLA 935 - 940 50 0.50

3-22230PLA 940 - 960 50 0.50

3-22223PLB 764 - 776 50 0.50

3-22224PLB 794 - 806 50 0.50

3-22225PLB 806 - 824 50 0.50

3-22226PLB 851 - 869 50 0.50

3-22227PLB 870 - 894 50 0.50

3-22228PLB 925 - 935 50 0.50

3-22229PLB 935 - 940 50 0.50

3-22230PLB 940 - 960 50 0.50

Table A1: Specification for 800 MHz Isolators (Compact Style).

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INSTALLATION

The isolators can be mounted on most types ofsurfaces but should not be physically locatedwhere they will not be exposed to moisture or very

high humidity. TXRX Systems isolators are wellshielded magnetically and may be mounted on

steel cabinets or panels.

The isolators can get quite hotduring operation. This can occurwhen an antenna system compo-

nent fails causing high reflectedpower which is then dissipated by

the isolator load. These loads canget hot enough to burn skin so

use caution when servicing thesesystems.

VERIFYING ISOLATOR FUNCTIONALITY

If you suspect there may be a problem with an iso-lator you can verify the functionality of the deviceby measuring its reverse isolation and insertion

loss. It is important to electrically remove the isola-tor from the system before testing. This is easily

accomplished by disconnecting the input and out-put cables.

WARNING: Do not make or breakcable connections to the isolator

while the circuit is under transmitpower. Shut down the transmitter

before servicing.

RECOMMENDED TEST EQUIPMENT

The following equipment or its equivalent is rec-ommended when verifying isolator functionality.

1) Spectrum Analyzer. Bird Technologies Signal

Hawk.

2) A pair of double shielded coaxial cable test

leads (RG142 B/U or RG223/U).

3) 50 Ohm load with at least -35 dB return loss(1.10 : 1) VSWR.

Measuring Reverse Isolation (S12)The reverse isolation of your isolator can be veri-

fied by performing the following procedure in astep-by-step fashion.

1) Make sure the transmitter associated with the

isolator is turned off.

2) Disconnect the input and output cable to the

isolator.

3) Connect a spectrum analyzer and tracking gen-

erator to the input and output ports of the isola-tor respectively, as shown in Figure A1.

4) Make sure that a 50 Ohm load is connected to

the load port of the isolator. If you are testingthe isolator on the bench make sure you con-

nect a load. If you are testing the isolator while itis still mounted on the system rack/cabinetleave the existing load connected.

5) Inject a test signal (-10 dBm) from the tracking

generator into the output port of the isolator.The test signal should sweep across the operat-ing bandwidth of the isolator.

6) Compare your displayed waveform against theexample shown in Figure A3 as well as thespecification listed in table A1.

Measuring Insertion Loss (S21)The insertion loss of your isolator can be verified

by performing the following procedure in a step-by-step fashion.

1) Make sure the transmitter associated with the

isolator is turned off.

2) Disconnect the input and output cable to the

isolator.

3) Connect a tracking generator and spectrumanalyzer to the input and output ports of the iso-

lator respectively, as shown in Figure A2.

4) Make sure that a 50 Ohm load is connected to

the load port of the isolator. If you are testingthe isolator on the bench make sure you con-

nect a load. If you are testing the isolator while itis still mounted on the system rack/cabinet

leave the existing load connected.

5) Inject a test signal into the input of the isolator

from the tracking generator which will sweepacross the operating bandwidth of the isolator.

The strength of the test signal should be -10dBm.

6) Compare your displayed waveform against the

example shown in Figure A4 and the specifica-tion listed in table A1.

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Tracking Generator

Spectrum Analyzer

Bird SignalHawk

50 Load

Figure A2: Verifying Insertion Loss.

Tracking Generator

Spectrum AnalyzerBird SignalHawk

50 Load

Figure A1: Verifying Reverse Isolation.

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Figure A4: Typical insertion loss waveform.

Figure A3: Typical reverse isolation waveform.

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CELCIUS FAHRENHEIT

105 221.0

104 219.2

103 217.4

102 215.6

101 213.8

100 212.0

99 210.2

98 208.4

97 206.6

96 204.8

95 203.0

94 201.2

93 199.4

92 197.6

91 195.8

90 194.0

89 192.2

88 190.4

87 188.6

86 186.8

85 185.0

84 183.2

83 181.4

82 179.6

81 177.8

80 176.0

79 174.2

78 172.4

77 170.6

76 168.8

75 167.0

74 165.2

73 163.4

72 161.6

71 159.8

70 158.0

69 156.2

68 154.4

67 152.6

66 150.8

65 149.0

64 147.2

63 145.4

62 143.6

61 141.8

60 140.0

59 138.2

58 136.4

57 134.6

56 132.8

55 131.0

54 129.2

53 127.4

52 125.6

51 123.8

50 122.0

49 120.2

48 118.4

47 116.6

46 114.8

45 113.0

44 111.2

43 109.4

42 107.6

41 105.8

40 104.0

39 102.2

38 100.4

37 98.6

36 96.8

35 95.0

34 93.2

33 91.4

32 89.6

31 87.8

30 86.0

29 84.2

28 82.4

CELCIUS FAHRENHEIT

27 80.6

26 78.8

25 77.0

24 75.2

23 73.4

22 71.6

21 69.8

20 68.0

19 66.2

18 64.4

17 62.6

16 60.8

15 59.0

14 57.2

13 55.4

12 53.6

11 51.8

10 50.0

9 48.2

8 46.4

7 44.6

6 42.8

5 41.0

4 39.2

3 37.4

2 35.6

1 33.8

0 32.0

-1 30.2

-2 28.4

-3 26.6

-4 24.8

-5 23.0

-6 21.2

-7 19.4

-8 17.6

-9 15.8

-10 14.0

-11 12.2

CELCIUS FAHRENHEIT

-12 10.4

-13 8.6

-14 6.8

-15 5.0

-16 3.2

-17 1.4

-18 -0.4

-19 -2.2

-20 -4.0

-21 -5.8

-22 -7.6

-23 -9.4

-24 -11.2

-25 -13.0

-26 -14.8

-27 -16.6

-28 -18.4

-29 -20.2

-30 -22.0

-31 -23.8

-32 -25.6

-33 -27.4

-34 -29.2

-35 -31.0

-36 -32.8

-37 -34.6

-38 -36.4

-39 -38.2

-40 -40.0

-41 -41.8

-42 -43.6

-43 -45.4

-44 -47.2

-45 -49.0

-46 -50.8

-47 -52.6

-48 -54.4

-49 -56.2

-50 -58.0

CELCIUS FAHRENHEIT

Celsius to Fahrenheit Conversion Table

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Return Loss vs. VSWR

Return Loss VSWR

30 1.06

25 1.11

20 1.20

19 1.25

18 1.28

17 1.33

16 1.37

15 1.43

14 1.50

13 1.57

12 1.67

11 1.78

10 1.92

9 2.10

Watts to dBm

Watts dBm

300 54.8

250 54.0

200 53.0

150 51.8

100 50.0

75 48.8

50 47.0

25 44.0

20 43.0

15 41.8

10 40.0

5 37.0

4 36.0

3 34.82 33.0

1 30.0

dBm = 10log P/1mW

Where P = power (Watt)

Insertion LossInput Power (Watts)

50 75 100 125 150 200 250 300

3 25 38 50 63 75 100 125 150

2.5 28 42 56 70 84 112 141 1692 32 47 63 79 95 126 158 189

1.5 35 53 71 88 106 142 177 212

1 40 60 79 99 119 159 199 238

.5 45 67 89 111 134 178 223 267

Output Power (Watts)

InsertionLoss

Free Space LossDistance (miles)

.25 .50 .75 1 2 5 10 15

150 68 74 78 80 86 94 100 104220 71 77 81 83 89 97 103 107

460 78 84 87 90 96 104 110 113

860 83 89 93 95 101 109 115 119

940 84 90 94 96 102 110 116 120

1920 90 96 100 102 108 116 122 126

Free Space Loss (dB)

Free space loss = 36.6 + 20log D + 20log FWhere D = distance in miles and F = frequency in MHz

Frequency(MHz)

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