KEY INTERLOCK IND
71.8-99.799 MHz FREQ KEY
69.3/70.3 MHz H5
SYNTHE-
INTERLOCK
500 kHz SIZER KEY LINETUNING
C1 CONTROL INTERNAL KEY LINE
CIRCUITS TUNE POWER C5 RECHANNEL B5
PULSE
115V AC OUT
9 28V DC OUT
11
PARALLEL TO SERIAL CONVERTER
1 kHz 10 kHz100 kHz1 MHz  AM/ USB/ SSB LSB
E6F6G6H6C7D7E7F7J6K6A7B7K5A6B6C6 D6A3B3
38394041495051524546474832333435 362524
YMLGNHEDPJFCUTSR KWF
1 kHz 10 kHz
100 kHz
1 MHzAM/SSB
D34371 A
(SH 3)
D34530
PTT FROM
AUDIO
INTEGRATION

5B
(SH 3)
55 C
(SH 3)
10 D
(SH 3)
26 E
(SH 3)
11 F
(SH 3) 56 G
(SH 3)
V
AGC
AM IFAND DET AMP
D345
60 C3 AGC
AUDIOD3 SELCAL OUTPUTSWITCH SQUELCH
E5
SQL/LAMP
TEST

AGC
SQ
PUSH-BUTTON

HEAD-57
PHONE
JACK

SSB IF
AND DET
AUDIO/SIDETONE OUTPUT
58 D1

E1 AVC
AMP
54

AUDIO
BAL
REG 20V
UNGND
MUX
MOD
DC AMP
A1
MIC INPUT

B1
GND

MIC
JACK

115V AC .A
12
+28V DC

115V AC .B POWER
23
115V AC .C

SUPPLY
+20V DC
37

12 NC RELAY
4 D5 INTERNAL
DRIVER
16

BLOWER
KEY LINE
ON/OFF
1810

CHASSIS GNDCOLLINS 628T-2( )
RELAY TRANSCEIVER
27 8 AC COLD
M226 HF-1 TRANSCEIVER (E2-3)
59 COLLINS 999W-2A TRANSCEIVER ADAPTER
D345 M898 HF-1 TRANSCEIVER ADAPTER (E2-3)
D419 D419
USB
ON/OFF RELAY  29. 9 9 9
OFF AM
RF
A

Z
SENS
PANEL
LIGHTS
LO USB/LSB

HI B RF SENS HF-1 CONTROL PANEL (P8-11)
HF Communication System Schematic
Figure 2 (Sheet 1)

RF SENS
SQUELCH
D125B
SELCAL AUDIO 26
M69 AUDIO ACCESSUNIT (E2-1)
D4287
AUDIO/SIDETONE HI 23
MIC AUDIO 6
ELECTRONIC SHELF(E2-1)
HF-1 AC.A115V ACESS ELEX
.B BUS-1
.C
HF-1 DC
28V DC
ESS ELEX
BUS-1

P18 LOAD CONTROLCENTER
28V DCFROM CONTROLSTAND PANELLIGHT CONTROL(P8)
A 737-300/400/500MAINTENANCE MANUAL
EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. ú

 23-11-00
 BEJ B-2531,B-2532  ú ú 08 Page 9 ú Nov 12/01
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A 737-300/400/500MAINTENANCE MANUAL

A 737-300/400/500MAINTENANCE MANUAL

A
737-300/400/500MAINTENANCE MANUAL
 (d)  
If the HF antenna coupler fails to tune properly, transmission will be inhibited. In this situation, when the key or PTT switch is activated, the KEY INTERLOCK lamp on the HF transceiver front panel will light to indicate an HF antenna coupler fault.

 (e)  
In the HF transceiver, mike audio is applied to the balanced modulator. Part of the audio that's being used to modulate the transmitter is routed to the audio/sidetone output system.

 (f)  
Within the balanced modulator, the audio signal modulates the 500-kHz injection signal from the frequency synthesizer. The double-sideband suppressed carrier 500-kHz output of the modulator is attenuated in AM mode by an electronic switch before being applied to a single sideband (SSB) mechanical filter. The filter removes the upper sideband (USB) and 500-kHz carrier passing only the lower sideband.

 (g)  
The output from the receiver/exciter is applied to a power amplifier through an ALC (automatic load control) attenuator. The power amplifier raises the 100-milliwatt PEP input to a nominally 400-watt PEP output. The power amplifier has protective circuits that provide almost instantaneous shutdown of the power amplifiers in the event of excessive power amplifier internal power dissipation.

 (h)  
The 400-watt PEP RF output is routed through a directional wattmeter and a transmit-receive relay to the external HF antenna coupler. Forward and reflected power detectors, within the directional wattmeter, provide voltages that are used to generate the ALC signal and to drive the power amplifier protection control circuit. The relay disconnects the receiver from the HF antenna coupler and connects the transmitter to the HF antenna coupler. Whenever the HF transceiver is in the transmit mode, an internal blower provides forced-air cooling to the transmitter circuits to prevent overheating.
　
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