i ·· ....... ·

VHF COMMUNICATION

GENERAL

Two Very High Frequency (VHF) radio communication systems are used to transmit and receive voice communicatio!l3, They are used primarily to contact airport control towers for takeoff and landing instructions and for enroute reporting. They are capable of communications over line­of-sight distances only, therefore, range for air-to-ground communi­catio!l3 is limited by aircraft altitude.

--

AffiCRAFT INSTALLATION

Power require !'llects and loca:iot!s are shown on the ~-c!:'aft inst:llla:ion drawing.

The primary components a::-e o.s fellows:

., Contr'Ji Pace~

Interchangeable com;JQnents a!:'e as follows:

• Traosceive,- COLU~S 6iS)'I- lC

• Control Panel COLlJ!'iS 313N:l

• Antenna COLUNS 522-1!35-012

VOL. VI 5-1 .,

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VHf CC»++ AIRCRAFi

INSTALlATICfl

.. .. ·

SYSTEM OPERATION (only one system is discussed}

The combination VHF COMM/VHF NAY control panel provides the necessary controls for operation of the VHF communication equipment. These controls are power (PWR) on-off, frequency selection, received audio volume control, and communications (COMM) test.

VHF' CCH4

. [ 116.000 l COMtO

VOL

·COMM TtST BUTTON

VHF' NAY

I lal.OOO l TEST

® 25 KHz

StLC:CT OR KNOB

VOLUME CONTROL

I

The power switch activates the system. Frequency selection is made by the I MHz and 25 KHz selector knobs. The selected frequency appears in the dial window. The headset volume is adjusted by the volume cont:·ol. The COMM TEST button, when pressed, allows noise to appear in the headsets. This provides a go-no-go check of the receiver.

With the system activated and the ;:>roper frequency selected, transmission is provided by selecting the dc.>u-~d syste:n on the intcrphoce rotary selec:or and pressing the mic button. Reception is provided by releasing the J::Cic button.

VOL. VI .. s-3

'· ... ...

SPECIFICATIONS

5-4

WILCOX 807

CHARACTERISTIC

Power requirements

Frequency Range

Transceiver

Number and spacing of channels

- , _Transceiver

Channeling time

Frequency selection

Output impedance

T:ansmitter output power

Type of emission

Type of modulation

Audio imput impedance

Sidetone level

Sensitivity

..

SPECIFICATION

27. SV DC + 10 percent; - 20 percent

116.00 to 149. 975 MHz

1360 channels 25 KHz apart

Less than 4 seconds

ARJNC (2 out of 5 wire)

52 ohms

25 watts , minimum

Amplitude, high I eve!

100 ohms

100 MW into 200 or 500 ohms at 100 percent modulation

3 microvolts for 6 db at 1000 Hz 30 percent modulation

VOL. VI

SPECIFICATIONS·

COLLINS 618M- l ()

CHARACTERISTIC

Power requirements

Frequency range

618M-l

618M-lA

6l8M- lB

G~M-lC

618M-lD

Number and spacing of channels

6l8M-l

618M- 1A

618M-1B

6!8M- 1C

618M-1D

Channeling time

Frequency selection

Output impedance

Transmitter output power

VOL; VI ..

SPECIFICATION

27. 5 V DC + 10 percent; - 20 percent

118. 00 to 135. 95 MHZ

116.00 to 149.95 MHZ

118. 00 to 135. 975 MHZ

116.00 to 149. 975.MHz

116. 00 to 135. 95 MHZ

3tl0 channels 5v lGiz a;:ar;

680 channels 50 ¥-'Iz apar·t

1360 c!laonels :!5 KHz apart

400 cnan:1els 50 K .. ~z apart

Less than 4 s ecocds

ARINC (2 out of 5 wire)

52 ohms

25 watts , minimum

5-5

..

SPECIFICATIONS (continued)

COLUNS 618M-l ( )

·-CHARACTERISTIC SPECIFICATION

Type of emission A3, AO

Type of >:nodulation Amplitude, high level

Audio Input impedance 150 ohms

Audio output impedance 600 ohms

Sidetone level . 100 MW 90 percent modulation ~.

Sensitivity 4 microvolts for 6 db at 1000 Hz

BLOCK DIAGRA .. \1 THEORY OF OPERATION

T?....:. .. Ns:\!ITTE R

A multi -channel VHF tr:msmit:er consists of a number of oscill:ltors, mixers, anti amplifiers . Combinations of .)scillator frequencies provide all possible tro.n.;;mit frcqut:r.cies . The selec~ed operating frequency s ignal level from the final mixer ~tage will be raised by RF amplifiers to the specified power output.

An audio modulating signal is supplied from a microphone through the i.:lter­phone system to the transmitter modulator circuits. The modulator circuits provide the signal amplification necessary to fully modulate the Radio Fre­quency (RF) carrier . The modulated RF carrier output is routed through a low pass filter, which suppresses harmonics and prevents transmission of spurious signals, to the antelllla for radiation. A portion of the modulated RF ot.~put is detected, amplified, and routed to the interphone system as side­tone. The sidetone signal gives the operator an Indication of transmitter operating condition .

•.

5-6 VOL. VI

· ..... _ ...

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CIRCUI TS CIRCUITS CIRCUITS

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B AS I C TRANSMITTER

ANP I.ITUDE MODUI.ATtD

VHr OUTI'UT

There is always definite relationships between the operating frequency, selected at the control panel, and the transmitter oscillators and mixers out­put frequencies. · These relationships can be stated as simple rules. The WILCOX 807 transceiver series will be used as a typical example to demon­strate the frequency selection scheme. The 807 transmitter section uses five crystal-controlled oscillators, a frequency doubler, an injection ampli­fier, and three mixers in its frequency: generating system. Frequency se­lection is accomplished by switching diodes controlled by the remote control panel using the 2 out of 5 wire grounding scheme per ARINC wiring specifications . The injection and RF amplifier stages are tuned to the correct freque ncies by · va=actors (voltage variable capactors). Output of the frequency generation systen::. (carrier frequency) is amplified in saccession by the RF amplifier, RF exciter amplifier, driver amplifier , and power amplifier. The output of the power amplifier (25 watts mirJ.mum) is applied to the antenna. Voice input signals' used to modulate the transmitter carrier are amplified to the required level by the modulator amplifier stages and used to modulate the RF carrier at the power amplifier stages. The transmitter output is filtered oy the lo"·-pass filter and monitored by the integral sidetone circuit.

The "Transmitter Block Diagram" shows ranges of frequencies for the o5cillators and mixers. However, for a particular transmitter channel, only one specific frequency within each range is present at each point in the frequency synthesis sceme.

VOL. VI .. 5-7

--------- ---

For transrn itter frequency synthesis, frequency selection is accomplished by switching the tens oscillator "on" or "OFF," switching between the two units - --oscillators {high and low), and by switching crystals in each active units, tenths, and hundredths OSCILLATORS. Crystal switching functions are performed by diodes acting as solid state switches. A total of 35 crystals are used in the transmitter frequency synthesis

The·~ oscillator output is 10 MHz in transmit operation. It is "on" when the selected transmit frequency is llX. XXX (X' s denote insignificant digits) or 14X. XXX MHz. It is OFF when the selected f requency is 12X. XXX or 13X. XXX MHz.

TtNTHS (0) T ENS (E:)

-. HUNDAIOS (A) THOUSANDTHS (F') 0 OA 5 ONL T

1 3 X CON T ROl

I'~E:QUENCY

X X v A

PANEL OISPLAY

.?. ;.~le l - Teas v3C~ !ator ou:;H;: equals D . 0 ~.L'iz when B is 1 or ·L

Either the high .!:!.!!.ill or the iow .!!.!!.!!§ osciiiator is selected for operation, depe.ndant u;:on the frequency selected at the control panel. For selected f-equencies between llX. X.'OC and 12::<. XXX, the low units oscillator is active. Even though either the high or low units oscillator is activated by the tens digit (B), their actual frequency is determined by the units digit (C) .

Ruie 3- Low units oscillator output equals 52.45 :MHz • Ct 2 when "B" is lor 2.

Rule 4 - Low units oscillator "OFF" when B is 3 or 4 .

Rule 5 - High units oscillator output equals 57.45 + C/ 2 when "B" is 3 or 4 .

.. 5-8 \ 'OL. VI

, __

Rule 6 - High units oscillator "OFF" when B is l or 2.

UNI TS

T ENS (B) (E) HUND!I tDS (A) THOUSANDTHS ( r)

0 011 5 OtU.T

1 2 5 X X X

CONT R OL PANEL FREQUENCY DISPLAY

The active units oscillator frequency is doubled and applied to the first injection mixer where it is mixed with the~ oscillator output. The output of the first injection mixer is applied to a tracked filter, which is varactor tuned to select the difference frequency when "B" is 1, to select the doubled units oscillator frequency when "B" is 2 or 3, and to select the sum frequency when "B" is 4. The frequency selected by the tracked filter is amplified and applied to the third injection mixer.

The tenthlroscillator operates at one of ten crystal controlled frequencies over a range of 19.70 to 20.6 MHz in 100KHz steps. The frequency of this oscillator is controlled by the tenths digit (D).

,, \TtNTHS (0)

C 0 N T R C L ? A H E L !'Rt:QU::: HCY DIS?LAY

Rule ; - Tenths oscillator output equals Ui. 7 ~ D.

Example: 19.7 + • 5 equals 20. ~ ~!Hz.

The output of the tenths oscillator is applied to the second injection mL'<er.

The hundredths osc illator operates a t one of four crystal controlled frec:;uencies over a range of 4. 525 to 4. 600 !\<1Hz. in 2~ KHz. steps. The frequency is con­trolled by the last two digits (E hundredths and F thousandths) of t~e selected operating frequency.

VOL. VI 5-9

1 2 5 CON TR OL

F' R E QU E NCY

\ THOU

HUNDII tDTHS (E)

SAH DTHS (F')

' '

5 2 5 P A N f:L D> ISPL A Y

Rule 8 - Hundredths oscill.ator output equals 4. 6 - E F

Example: 4. 6- . 025 equ~ls 4. 575 MHz.

The output of the hundredths and tenths oscillators are mixed in the second injection mix~r. A varactor controlled tracked filter in the mixer output selects the difference frequency which is applied to the third injection mixer where it is mixed with the combined outputs from the~ and~ oscillators. The sum of the two signals is selected by a tracked filter and is within the frequency range of 116.00 to 149.975 MHz (the selected operating frequency). The carrier frequency is then amplified by the RF amplifiers, voice modulated, and transmitted.

RECEIVER .

A VHF superhetrodyne receiver must nave amplifiers, oscillators, mb:ers, and a dPmodulator. The oscillator inject :On frequency must be offset from :he received frequency by an amount qual to the Inter:nediate Frequency (IF). T!:l is of!set can he accomplished with occ or :nore oscillators and mb:ers (sing!e conve!"5ion, riu3.l cocversiO:l. c:c .). Becacse cf tnis off sec, : he recei·:er f:'(!C::..:~::.cy s..:heme must diller from t!:~ ~ransmit:er i requency scheme.

The received signal from the antenna, in a typical mwti-channel VHF recei\·er, •s ;.ppEed ::> :he R:: c ircdts where i~ is iil!ered, a::nplified, and sent to t!:e first mixe:-. Also into the !i:-st mLxer is an injection frequency, from a tunable oscillator, that is offset from the received frequency by some amount (IF). Most receivers use two or three frequency conversion stages, thus two or three IF's, for image frequency rejection. The output of each mixer goes through frequency selecting filters and one or more stages of IF amplification. The IF filter and amplification stages determine the receiver bandpass (selectivity). The output of the final IF stage is demodulated and the resulting audio is amplified and routed through the control panel volume control to the interphone and/or headphones or loudspeakers. The output of the final IF stage is also detected to c r eate a D-e voltage, proportional to received signal stre!lgth, which Ls used ae degenerative feedback to the RF a nd IF amplifier

.. 5- 10 VOL. VI

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ANT £IIIlA sv Ill" CIRCUI TS

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CIRCUITS

AUDIO OUTPUTS

RECEIVER

As with the transmitter, ther e is alw~s definite relationships between the operating frequency, selected at the control panel, and the frequency of the receiver's oscillators and mixers. These relationships can also be stated in rules. The receiver portion of the Wilcox 307 transceiver series will be used as a typical example.

The 807 receiver section is a crystal controilec, tl'iple con'le.?sion receive:-. To achieve triple conversion, it uses six c:-ystal contl'o iled oscillators (a total of 36 crystals are used in t.'le r eceiver ), a f:-eq~er.c:; doubier, :m injection amplifier, and five mixen. The cooversi0:.1 sys;eu:: ;; roc::Ce<i a V~!acie IF (VI F ) of 15 . 1 to 16. 075 MHz, a fixed l'-' of 3. ~ ~!:1 ::. a::c !l s~conc ~L'tec :F '): 455 KHz. F'oilowin~ t!:e co~·;e:-s~vr: c i...-~ ::.~:s :t::e :::.: t:"e ~F ::.."npi.:...:ie:-.; , au :::::iic detector. ACC cont:-ol C!:Ctlit, sqt:.~lc t: =:~· :- ~1.: 2! . .: ::tc: .. ,e ~ ! .:::~.:.: c::- , 2:::~ :. :.::- ~~~

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by two-out-of-five wire digital binary (A.'ill':c wlru~g 5pecil:cation) i:ll,•rmation controlling Ciodes which act as solid state swit.ches.

Basically the receiver injection frequency generating sct.eme is :~.e sa.::J.e as the transmitter carrie~ frequency generati'1g scheme. The~ oscElator is switched "on" or "OFF" , either the .!!.!&!!.or low units oscillato.- is active, crystals are switched in each of the active .!!!!ll2. ~. aod bundrP.dths oscillators. Varactor tuned filters, rather than mechanical tuning capacitors, are used in the RF and injec tion stages. The rules for the receiver frequency scheme are the same as tbe rules for the transmitter. However, the actual fr equencies Involved will be d.U!erent to account for the required IF offset. With reference to the selected frequency on the control panel we see that

.. 5- 12 VOL. VI

there are the following frequency rules:

Rule 1 - Tens oscillator output equals 9. 999 MHz when "B" is 1 or 4.

Rule 2 ·Tens oscillator "OFF" when "B" is 2 or 3.

Rule 3- Low units oscillator output equals 52.45 MHz + C/2 when "B" Is 1 or 2.

Rule 4 - Low units oscillator "OFF" when " B" is 3 or 4.

Rule 5 - High units oscillator output equals 57.45 MHz + C/2 when "B" is 3 or 4.

Rule 6 - High wiits oscillator "OFF" when "B" is 1 or 2.

Rule 7 - Tenths oscillator output equals 10.101 MHz + "D".

Rule 8 -Hundredths oscillator output equals 8 . 499 MHz + "EF" .

VOL . VI

TtNS HU~O~tOTHS (E) HUNO~tDS (A) THOUSANDTHS (r)

"~~~--~--~~~~~.,~~ 0 o• 5 ONLT

..

1 2 5 CONTROL

F'REQUENCY

X X X P A N E L DISP L AY

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