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 23-12-00
 ALL  ú ú 11 Page 4 ú Dec 20/96
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
757
MAINTENANCE MANUAL

+20V
28V DC

PWR +12V
RF SENSOR
+5V-12V
SPLY
VHF COMM
CIRCUIT AUDIO A
P11 RF
RF (FRCV) AF AMP
VHF COMM

RF
ATTEN
IFAGC
TFR

SQUELCH 118.00
118.00
COMM TEST PHONE KEYEVENT
SOL LAMP
TEST
TFR

FLT DATAACQUISITION UNITG 5V AC
G
POWER
SUPPLY

VHF ANTENNAI/P PORT B
ARINC 429
429
COMM

RED
TEST

XMTR RCVR
SELF CONTROL +5V TEST INPUT CIRCUIT FAIL
SOL/LAMP
TEST
RFOFF
FREQUENCY DATA SEL
SELECTOR
(FLO)
FREQUENCY

ENCODER
REF FWD
GREEN
SELECTOR
CONTROL LRU
LRU PASS
ENCODER
INPUT PASS
NC
FAIL
PHONE MIC
I/P PORT A 429
INDICATESRCVR
FREQUENCY YSWR SYNTHESIZER FOR 1 SEC
VHF-700 TEST
AF VHF COMM CONTROL PANEL
MIC KEY
DATA KEY RET KEY VOX DATA SEL SELECT
FWD
REF LOGIC TEST +28V
OFF
DATA KEY
AGC NC
HI DATA IN RF DIRECTIONALRF
DATAAF
MODULATOR
RF
COUPLER &LO LPF (FXMT) SELCAL DECODER XMT AF
SIDETONE
A
DIRECTOR PTT
KEY EVENT
PTT
HI MIC IN
MIC HIGH
LO
AUDIO SIDE TONE
+16V DC

TO OTHER ASPS
VHF TRANSCEIVER

CAPTS ASP
VHF Communication Schematic (Example)
Figure 2 (Sheet 1)

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 GUN 001-050, 052-999 ú 23-12-00
 ú ú 09 Page 5 ú Jan 28/02
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
D04819
A
757
MAINTENANCE MANUAL

POWER
28V DC DC SUPPLY
VHF COMM AUDIOFILTERP11 COMPRESSOR NC
HEADPHONE
JACK
AUDIO SIDETONE
MIC HIGHKEY EVENT
DC
PTT
MODULATOR

VSWRDETECTOR
FLT DATACAPT'S ASP
HAND MICACQUISITION UNIT
TO OTHER ASPS
JACK
DC
TFR

POWERLEVELER DC
GT/R SWITCH
VHF ANTENNAG
RF POWERSUPPLY
PRESELECTOR
BENDIXVHF COM AIR TRANSPORTAVIONICS
DC VOLTS
ARINCMINI-COMPUTER
429

PORT B BUILT-IN TEST TRANS-
COM XMTR
MIXER
CEIVER CIRCUITS MIC DATA IN FAULT ANALYSIS
PHN
FREQUENCY

FREQUENCY AND
SQ/TEST
SELECTOR

SELECTOR DATA INTERFACE
ENCODER CRYSTALENCODER FILTERIF RSV DETECTORVHF COMM CONTROL PANEL VHF COMM
SYNTHESIZER
TFR

DATA
118.00
118.00
SQUELCH DISABLE SELCAL DECODERAIR
NC GND
VHF TRANSCEIVER AIR/GNDRELAY
VHF Communications System Schematic (Example)
Figure 2 (Sheet 2)

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 23-12-00
 ú ú 12 Page 6 ú Jan 28/02
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
D04828
A

757
MAINTENANCE MANUAL

 (d)  
To transmit, a PTT switch (AMM 23-51-00/001) for the microphone being used is pushed. The PTT switch controls circuits within the transceiver which disconnect the receiver circuits, and connect the transmitter circuits to the antenna. Transmission begins when audio signals are impressed on the microphone circuits. Sidetone is provided to the crewmember's headset to indicate proper operation of the transmitter. When the PTT switch is released, the system returns to the receive mode.

 (e)  
Frequency tuning data from the control panel is transmitted to the transceiver by an ARINC 429 digital data bus. The data bus provides one-way digital data transmission between components.

 (f)  
The transceivers accept microphone and PTT inputs from the audio selector panels, and from a microphone jack located on the front panel of the transceiver. The antennas transmit and receive rf signals. These signals are distributed by the transceivers. The transceivers provide audio signals to the audio selector panels, and to the headphone jack on the transceiver's front panel. Each time a microphone is keyed (by pressing the PTT switch), an ATC event signal is recorded by the flight data recorder.
　
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