Vertex Standard VX-131, VX-132 Service Manual

FM Business Two-Way Radio

VX-131/-132

VHF Model

Service Manual

©2004 VERTEX STANDARD CO., LTD. EC059N90A

VERTEX STANDARD CO., LTD.

4-8-8 Nakameguro, Meguro-Ku, Tokyo 153-8644, Japan

VERTEX STANDARD

US Headquarters

10900 Walker Street, Cypress, CA 90630, U.S.A.

YAESU EUROPE B.V.

P.O. Box 75525, 1118 ZN Schiphol, The Netherlands

YAESU UK LTD.

Unit 12, Sun Valley Business Park, Winnall Close
Winchester, Hampshire, SO23 0LB, U.K.

VERTEX STANDARD HK LTD.

Unit 5, 20/F., Seaview Centre, 139-141 Hoi Bun Road,
Kwun Tong, Kowloon, Hong Kong

VX-131 VX-132

Introduction

This manual provides technical information necessary for servicing the VX-131 and VX-132 VHF FM Transceiver.

Servicing this equipment requires expertise in handling surface-mount chip components. Attempts by non-qualified
persons to service this equipment may result in permanent damage not covered by the warranty, and may be illegal in
some countries.

Two PCB layout diagrams are provided for each double-sided circuit board in the transceiver. Each side of is referred to
by the type of the majority of components installed on that side (“leaded” or “chip-only”). In most cases one side has only
chip components, and the other has either a mixture of both chip and leaded components (trimmers, coils, electrolytic
capacitors, ICs, etc.), or leaded components only.

While we believe the technical information in this manual to be correct, VERTEX STANDARD assumes no liability for
damage that may occur as a result of typographical or other errors that may be present. Your cooperation in pointing out
any inconsistencies in the technical information would be appreciated.

Contents

Specifications................................................... 2

Exploded View & Miscellaneous Parts ...... 3

Programming the Channel Data .................. 4

Cloning ............................................................. 6

Block Diagram ................................................. 7

Circuit Description ................................. 9

Alignment ............................................... 13

MAIN Unit

Circuit Diagram ....................................................... 21

Parts Layout ............................................................. 23

Parts List ...................................................................25

1

Specifications

General

Frequency Range: 150 - 174 MHz
Number of Channels: 1 channel (VX-131),

2 channles (VX-132)

Channel Spacing: 12.5 / 25 kHz
Power Supply Voltage: 7.5 VDC ± 10%
Operating Temperature Range: –22 °F to +140 °F (–30 °C to +60 °C)
Frequency Stability: ±2.5 ppm
Dimensions (WHD): 2.3“ x 4.7“ x 1.2“ (58 x 120 x 31 mm)
Weight (approx.): 12.7 oz (360 g) w/FNB-64, antenna, and belt clip

Receiver (Measurements made per EIA standard TIA/EIA-603)

Circuit Type: Double-Conversion Superheterodyne
Intermediate Frequencies: 1st: 44.25 MHz,

2nd: 450 kHz

Sensitivity: 0.25 µV (EIA 12 dB SINAD)

0.35 µV (20 dB Quieting)

Selectivity (–6 dB /–60 dB): 12 kHz / 30 kHz (25 kHz),

9 kHz / 30 kHz (12.5 kHz)

Adjacent channel selectivity: 65 dB (25 kHz),

60 dB (12.5 kHz)

Intermodulation: 65 dB
Spurious and Image Rejection: 65 dB
Hum & Noise 45 dB
Audio output: 500 mW @4 Ohms, 10 % THD

Transmitter (Measurements made per EIA standard TIA/EIA-603)

Power output: 2.0 W
Modulation: 16K0F3E (25 kHz),

11K0F3E (12.5 kHz)

Conducted Spurious Emissions: 60 dB Below Carrier
FM Hum & Noise: 40 dB (25 kHz)

35 dB (12.5 kHz)

Audio distortion (@ 1 kHz): <5 %

Measurements per EIA standards unless noted above. Specifications subject to change without notice or obligation.

2

Exploded View & Miscellaneous Parts

RA0173500
CAP



R6147510
RING NUT

RA0296100
VOLUME KNOB

RA0631200
FRONT CASE ASSY (VX-132)
(w/PTT KNOB)



RA029430A
RUBBER PACKING

RA0309800
MYLAR SHEET (SP)





RA0631300
FRONT CASE ASSY (VX-131)
(w/PTT KNOB)

RA0294200
PTT KNOB

RA0110200
HOLDER RUBBER

RA0294200
PTT KNOB



CB2910001 (VX-131)











CB2910002 (VX-132)
MAIN UNIT

RA0623900
SPONGE RUBBER



RA0351700
TERMINAL PLATE (+)

RA010340B
TERMINAL HOLDER



RA0351600
TERMINAL PLATE (–)

RA0533600
SHEET (GP1-1.0-6X6)









CP8021001
BELT CLIP ASSY



Non-designated parts are available only as part of a designated assembly.

RA0123500
LATCH NAIL B

RA029430A
RUBBER PACKING

RA029310D
REAR CASE ASSY
(w/SMA CONNECTOR, TERMINAL PLATE L,

PAN HEAD SCREW M2X3NI)

CAUTION



REF. VXSTD P/N Description Qty.

 U44104002 TAPTITE SCREW M2X4NI 10

 U20206007 BINDING HEAD SCREW M2.6X6B 2

 U24110002 TAPTITE SCREW M2X10NI 2

 U02206007 SEMS SCREW SM2.6X6B 2

 U00103002 PAN HEAD SCREW M2X3NI 1

ACCESSORIES

VXSTD P/N

AAA46X001

A14170002

AAE24X002

FNB-64 Ni-Cd Battery Pack
NC-77B Overnight Battery Charger
ATV-8B VHF Antenna

DESCRIPTION

3

Programming the Channel Data

The VX-131/-132 transceiver allows you to change the channel frequency and its CTCSS/DCS status. Also, you may select
the channel bandwidth (wide/narrow) of all VHF frequencies and some UHF frequencies (see the channel table).

Programming the Operation Frequency

 Turn the radio on while pressing and holding in the

PTT and MONITOR buttons.

 Hold in the PTT and MONITOR buttons until the LED

indicator glows orange (approx. 3 seconds), then re­lease the PTT and MONITOR buttons.

 If your radio is the VX-132 (two channel model), toggle

the CH switch to the channel (“1” or “2”) on which
you want to program the new channel frequency.

 Press the MONITOR button momentarily; the LED in-

dicator will change to red and the radio will emit a
“channel confirmation beep” that describes the cur­rent channel programming, according to the follow­ing rule.

)

FIRST AND SECOND BEEPS (LOW PITCH TONES

NUMBER

BANDWIDTH

Wide

CONFIRMATION BEEP

–––

0
1
2
3
4

(two seconds






THIRD BEEPS (HIGH PITCH TONES

CONFIRMATION BEEPBANDWIDTH

)

NUMBER

5
6
7
8
9

Narrow

Examples:

Channel Number 6, Bandwidth “Wide”:

––– –

0 6 Wide



Channel Number 18, Bandwidth “Narrow”:



1 8 Narrow

–

   

 Press the PTT button once each for each quantity of

“ten” in the channel number (i.e. press PTT three times
for channel 3n); when finished entering the “tens”
place, a confirmation beep will be heard. Immediately
after the confirmation beep, press the PTT button once
each to complete the “ones” in the channel number
(i.e. press PTT twice for channel 32, after receiving
the first confirmation beep). Now press the PTT but­ton once or twice, corresponding to the bandwidth
(once for “Narrow” or twice for “Wide”). When entry
is complete, the radio will emit a confirmation beep.
In this programming sequence, if you wish to enter
the number “0,” press and hold in the PTT button until
the channel confirmation beep (long tone) is heard. If
the channel is a “Narrow-only” channel (such as UHF
channel “03”), you do not need to enter the bandwidth.

Examples:

Channel Number 6, Bandwidth “Wide”:

–––

0 6 Wide

     

Channel Number 18, Bandwidth “Narrow”:

        

1 8 Narrow

: C

HANNEL

CONFIRMATION BEEP



–



–



–



–



)

: B

ANDWIDTH

CONFIRMATION BEEP



 If the channel programming process fails, the radio

will emit an alert tone (beep-beep-beep:

  

).

You may check the channel number by pressing the
MONITOR button. The radio will respond with the
channel programming confirmation beeps according
to the chart at the beginning of this section.

Programming the CTCSS/DCS/ARTS Status

 Turn the radio on while pressing and holding in the

PTT and MONITOR buttons.

 Hold in the PTT and MONITOR buttons until the LED

indicator glows orange (approx. 3 seconds), then re­lease the PTT and MONITOR buttons.

 If your radio is the VX-132 (two channel model), toggle

the CH switch to the desired channel (“1” or “2”) on
which you want to program the CTCSS/DCS tone or
ARTS Operation.

 Press and hold in the MONITOR button for 2 seconds;

the LED indicator will change to green, and the radio
will emit a CTCSS/DCS/ARTS status confirmation
beep that describes the current CTCSS/DCS/ARTS sta­tus, according to the following rule (see also the
CTCSS/DCS/ARTS Chart):

CTCSS/DCS/ARTS STATUS NUMBER

NUMBER

Examples:

CTCSS/DCS “OFF” (000):

CTCSS “88.5 Hz” (Tone 009 per CTCSS/DCS Chart):

DCS “023” (Tone 051 per CTCSS/DCS/ARTS Chart):

 Press the PTT button once each for each quantity of

100 in the CTCSS/DCS/ARTS status code, per the
CTCSS/DCS/ARTS Chart; as before, when entry is
completed for the “100s” place, the radio will emit a
confirmation beep. Now press the PTT button once
each for each quantity of tens in the CTCSS/DCS/ARTS
status code number, get the confirmation beep, then
press the PTT button once each to set the “ones” place,
after which the final confirmation beep will be heard.
In this entry sequence, to enter the number “0,” press
and hold in the PTT button until the channel confir­mation beep (long tone) is heard.

0
1
2
3
4

CONFIRMATION BEEP

–––

(two seconds






)

NUMBER

5
6
7
8
9

––– ––– –––

000

––– ––– –

009

–––

05 1

    

   

CONFIRMATION BEEP



–



–



–



–



4

Examples:

Enter the CTCSS “88.5 Hz” (009):

––– –––

009

        

Enter the DCS code “023” (051)

–––

05 1

    

Activate ARTS using DCS code “165” (163):

       

16 3

If the CTCSS/DCS/ARTS status programming process
fails, the radio will emit an alert tone (beep-beep-beep:

).

  

 You may check the CTCSS/DCS/ARTS status by press-

ing and holding in the MONITOR button. The radio
will respond with the CTCSS/DCS confirmation beeps
according to the chart at the beginning of this section.

Programming the Channel Data

CH

1
2

CH

01
02
03
04
05
06
07
08
09
10

Code #

001
002
003
004
005
006
007
008
009
010
011
012
013
014
015
016
017
018
019
020
021
022
023
024
025

VX-131 DEFALUT SETTING

Frequency

(

MHz

151.6250
–

Frequency

(

MHz

151.6250

151.9550

154.5700

154.6000

151.7000

151.7600

151.5125

151.6550

151.6850

151.7150

)

)

W/N
W/N
W/N
W/N
W/N
W/N
W/N
W/N
W/N
W/N

CTCSS

67.0 Hz

69.3 Hz

71.9 Hz

74.4 Hz

77.0 Hz

79.7 Hz

82.5 Hz

85.4 Hz

88.5 Hz

91.5 Hz

94.8 Hz

97.4 Hz

100.0 Hz

103.5 Hz

107.2 Hz

110.9 Hz

114.8 Hz

118.8 Hz

123.0 Hz

127.3 Hz

131.8 Hz

136.5 Hz

141.3 Hz

146.2 Hz

151.4 Hz

BW

W

BW

channels are non-EIA/TIA standard codes

CTCSS/

DCS
OFF

–

–

VHF MODEL CHANNEL CHART

Red

Blue

–
–
–
–
–
–

CH

11
12
13
14
15
16
17
18
19
20

CTCSS

156.7 Hz

159.8 Hz

162.2 Hz

165.5 Hz

167.9 Hz

171.3 Hz

173.8 Hz

177.3 Hz

179.9 Hz

183.5 Hz

186.2 Hz

189.9 Hz

192.8 Hz

196.6 Hz

199.5 Hz

203.5 Hz

206.5 Hz

210.7 Hz

218.1 Hz

225.7 Hz

229.1 Hz

233.6 Hz

241.8 Hz

250.3 Hz

254.1 Hz

Color

Purple

Green

Code #

026
027
028
029
030
031
032
033
034
035
036
037
038
039
040
041
042
043
044
045
046
047
048
049
050

VX-132 DEFALUT SETTING

Frequency

(

MHz

151.6250

151.9550

Frequency

(

151.7450

151.7750

151.8650

151.8950

151.9250

152.7000

154.4900

154.5150

154.5400

154.6000

MHz

)

)

Code #

051
052
053
054
055
056
057
058
059
060
061
062
063
064
065
066
067
068
069
070
071
072
073
074
075

BW

W
W

BW

W/N
W/N
W/N
W/N
W/N
W/N
W/N
W/N
W/N
W/N

CTCSS/

DCS
OFF
OFF

Frequency

CH

(

MHz

21

154.6550

22

158.4000
–
–
–
–
–
–
–
–

CTCSS/DCS/ARTS STATUS CODE CHART

DCS

023
025
026
030
032
036
043
047
051
053
054
065
071
072
073
074
114
115
116
122
125
131
132
134
143

)

–
–
–
–
–
–
–
–

Code #

076
077
078
079
080
081
082
083
084
085
086
087
088
089
090
091
092
093
094
095
096
097
098
099
100

BW

W/N
W/N

–
–
–
–
–
–
–
–

DCS

145
152
155
156
162
165
172
174
205
212
223
224
225
226
243
244
245
246
250
251
252
255
261
263
265

Code #

101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125

DCS

266
271
274
306
311
315
325
331
332
343
346
351
356
364
365
371
411
412
413
423
431
432
435
445
446

Code #

126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150

DCS

452
454
455
462
464
465
466
503
506
516
523
526
532
546
565
606
612
624
627
631
632
654
662
664
703

Code #

151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174

000

DCS

712
723
731
732
734
743
754

ARTS (023)
ARTS (043)
ARTS (071)
ARTS (116)
ARTS (143)
ARTS (165)
ARTS (224)
ARTS (246)
ARTS (263)
ARTS (311)
ARTS (346)
ARTS (411)
ARTS (435)
ARTS (462)
ARTS (516)
ARTS (606)
ARTS (654)

OFF

5

Cloning

The VX-131/-132 series includes a convenient “Cloning” feature, which allows the programming data from one transceiv­er to be transferred to another VX-131/-132 series. Here is the procedure for cloning one radio’s data to another.

1. Turn both transceiver off.

2. Remove the plastic cap and its two mounting screws

from the MIC/SP jack on the right side of the trans­ceiver. Do this for both transceivers

3. Connect the optional CT-27 cloning cable between the
MIC/SP jacks of the two transceivers.

4. Turn the radio on while pressing and holding in the
MONITOR button.

5. Hold in the MONITOR button until the LED indicator
blinks orange (approx. 5 seconds), the release the
MONITOR button. Do this for both transceiver (the
order of the switch-on does not matter).

6. On the Destination transceiver, press the MONITOR

button. The LED indicator will change to green.

7. Press the PTT button on the Source transceiver, the

LED indicator will change to red, and the data will be
transferred.

8. If there is a problem during the cloning process, the
LED indicator will blink green; check your cable con­nections and battery voltage, and try again.

9. If the data transfer is successful, the LED indicator
return to blinking orange. Turn both transceivers off
and disconnect CT-27 cable. You can then turn the
transceivers back on, and begin normal operation.

10. Replace the plastic cap and its two mounting screws.

Optional Cloning Cable CT-27

6

Block Diagram

7

Block Diagram

Note

8

Circuit Description

Receive Signal Path

Incoming RF signal from the antenna jack is delivered to
the MAIN Unit and passes through a low-pass filter con­sisting of coils L1003 and L1006, capacitors C1009, C1012,
C1020, C1023, and C1030, and antenna switching diodes
D1006 and D1007 (both HSU277).

Signals within the frequency range of the transceiver en­ter a varactor-tuned band-pass filter consisting of coils
L1011 and L1012, capacitors C1062, C1064, C1075, C1081,
and C1084, and diodes D1009, D1010, D1012, and D1013
(all HVC355B), then amplified by RF amplifier Q1014
(2SC5006) and enter a varactor-tuned band-pass filter con­sisting of coils L1019 and L1021, capacitors C1096, C1099,
C1108, and C1113, and diodes D1019, D1020, D1021, and

D1022 (all HVC355B), before 1st mixing by 1st mixer
Q1026 (3SK320).

Buffered output from the VCO Q1003 (2SC5231) is am-
plified by Q1006 (2SC5005) to provide a pure 1st local
signal between 194.25 and 218.25 MHz for injection to the
1st mixer Q1026 (3SK320). The 44.25 MHz 1st IF signal
then passes through monolithic crystal filter XF1002 to
strip away all but the desired signal. The filtered 1st IF
signal is amplified by Q1033 (2SC4215Y).

The amplified 1st IF signal is applied to FM IF subsystem
IC Q1040 (TA31136FN), which contains the 2nd mixer,
2nd local oscillator, limiter amplifier, noise amplifier, and
RSSI amplifier.

A 2nd local signal is produced from the PLL reference/
2nd local oscillator of 14.60 MHz crystal X1001. The 14.60
MHz reference signal is tripled by Q1040 (TA31136FN),
capacitor C1173, and coil L1030, then resulting the 43.8
MHz second local signal delivered to mixer section of
Q1040 (TA31136FN) which produce the 450 kHz 2nd IF
mixed with the 1st IF signal.

The 2nd IF signal passes through the ceramic filter CF1001
(for “Narrow” bandwidth channels) or CF1002 (for
“Wide” bandwidth channels) to strip away unwanted
mixer products, and is then applied to the limiter amplifi­er in Q1040 (TA31136FN), which removes amplitude vari-
ations in the 450kHz IF, before detection of the speech by
the ceramic discriminator CD1001.

Detected audio from CD1001 is applied to the audio high­pass filter Q1030 (LM2902PW), and then passes through
the AF mute switch Q1037 (2SA1586Y), de-emphasis cir-
cuit consisting of resistor R1176 and Capacitor C1136, and
volume control to the audio amplifier Q1041 (NJM2070M),
which provides up to 0.5 Watts to the internal 4-Ω loud­speaker or the optional headphone.

Squelch Control

The squelch circuitry consists of a noise amplifier and
band-pass filter within Q1040 (TA31136FN) and noise
detector D1026 (1SS355).

When no carrier received, noise at the output of the de­tector stage in Q1040 (TA31136FN) is amplified and band-
pass filtered by the noise amplifier section of Q1040
(TA31136FN) and the network between pins 7 and 8 of
Q1040 (TA31136FN), and then rectified by D1026
(1SS355).

The resulting DC squelch control voltage is passed to pin
37 of the microprocessor Q1013 (M37516F8HP). If no car-
rier is received, this signal causes pin 20 and 24 of Q1013
(M37516F8HP) to go high. Pin 24 signal disable the sup­ply voltage of the audio amplifier Q1041 (NJM2070M).
Thus, the microprocessor blocks output from the audio
amplifier, and silences the receiver while no signal is be­ing received (and during transmission, as well). Pin 20
signal hold the green (Busy) half of the LED D1023 (12-
22SURSYGC) to off.

When a carrier appears at the discriminator, noise is re­moved from the receiver output, causing pin 37 of Q1013
(M37516F8HP) to go low and the microprocessor to acti­vate the green (Busy) half of the LED D1023 (12-
22SURSYGC) via Q1013 (M37516F8HP).

The microprocessor Q1013 (M37516F8HP) checks for the
CTCSS or DCS code squelch information. If the CTCSS or
DCS is not activated, or the received tone or code matches
that programmed, allows audio to pass through the au­dio amplifier Q1041 (NJM2070M) to the loudspeaker by
enabling the supply voltage to it via Q1039 (CPH6102).

Transmit Signal Path

Speech input from the microphone passes through a high­pass filter Q1017 (LM2902PW-2) and AF mute switch
Q1012 (2SA1586Y) to Q1001 (M62364FP) which adjust
the microphone gain. The adjusted audio passes through
a pre-emphasis circuit consisting of resistor R1063 and Ca­pacitor C1074 to the limiter amplifier Q1017 (LM2902PW-

3). The limited audio is applied to a low-pass filter Q1017
(LM2902PW-1/-4), then return to Q1001 (M62364FP)
which adjust the deviation level.

The audio signal is applied to varactor diode D1005
(HVC350) which which frequency modulates the VCO

Q1003 (2SC5231). The modulated signal from the VCO
Q1003 (2SC5231) is buffered by Q1006 (2SC5005), then

passes through the T/R switching diode D1014 (DAN235E)
to the driver amplifier Q1016 (2SC5227) and Q1019
(RD01MUS1), then amplified transmit signal is applied
to the final amplifier Q1024 (RD07MVS1) up to 2 watts
output power.

9

Circuit Description

The transmit signal then passes through the antenna switch
D1004 (RLS135) and is low-pass filtered to suppress har-
monic spurious radiation before delivery to the antenna.

CTCSS/DCS Signal Path

If a CTCSS tone encoder is enabled, the CTCSS tone gen­erated by Q1013 (M37516F8HP), then delivered to VCO
Q1003 (2SC5231) and TCXO X1001 for CTCSS modulat­ing.

If a DCS encoder is enabled, the DCS code is generated by
microprocessor Q1013 (M37516F8HP), then delivered to
TCXO X1001 for DCS modulating.

Automatic Transmit Power Control

Current from the final amplifier is sampled by R1136,
R1139 and R1142, and is rectified by Q1029 (IMZ2A). The
resulting DC is fed through the Automatic Power Con­troller Q1031 (FMW1) to the drive amplifier Q1019
(RD01MUS1) and final amplifier Q1024 (RD07MVS1), for
control of the power output.

Transmit Inhibit

When the transmit PLL is unlocked, pin 7 of PLL IC Q1005
(MB15A02PFV1) goes to logic “Low”, and unlock detec­tor Q1010 (2SA1586) goes to logic “High”. The resulting
DC unlock control voltage is passed to pin 14 of the mi­croprocessor Q1013 (M37516F8HP). While the transmit
PLL is unlocked, pin 22 of Q1013 (M37516F8HP) remains
high, which turns off Q1020 (CPH6102) and the Auto­matic Power Controller Q1031 (FMW1) to disable the sup­ply voltage to the drive amplifier Q1019 (RD01MUS1) and
final amplifier Q1024 (RD07MVS1), thereby disabling the
transmitter.

PLL Frequency Synthesizer

The PLL circuitry on the Main Unit consists of VCO Q1003
(2SC5231), VCO buffer Q1006 (2SC5005), and PLL IC
Q1005 (MB15A02PFV1) which contains a reference divid-
er, serial-to-parallel data latch, programmable divider,
phase comparator and charge pump.

While receiving, VCO Q1003 (2SC5231) oscillates be-
tween 194.25 and 218.25 MHz according to the pro­grammed receiving frequency. The VCO output is buff­ered by Q1006 (2SC5005), then applied to the prescaler
section of Q1005 (MB15A02PFV1). There the VCO signal
is divided by 64 or 65, according to a control signal from
the data latch section of Q1005 (MB15A02PFV1), before
being sent to the programmable divider section of Q1005
(MB15A02PFV1).

The data latch section of Q1005 (MB15A02PFV1) also re-
ceives serial dividing data from the microprocessor Q1013
(M37516F8HP), which causes the pre-divided VCO sig­nal to be further divided in the programmable divider
section, depending upon the desired receive frequency,
so as to produce a 2.5 kHz, 5 kHz, or 6.25 kHz derivative
of the current VCO frequency.

Meanwhile, the reference dividers section of Q1005 di­vides 14.60 MHz reference frequency from the TCXO Unit
X1001, by 5840 (or 2920 or 2336) to produce the 2.5 kHz
(or 5 kHz or 6.25 kHz) loops reference (respectively).

The 2.5 kHz (or 5 kHz or 6.25 kHz) signal from the pro­grammable divider (derived from the VCO) and that de­rived from the reference oscillator are applied to the phase
detector section of Q1005 (MB15A02PFV1), which pro-
duces a pulsed output with pulse duration depending on
the phase difference between the input signals.

Spurious Suppression

Generation of spurious products by the transmitter is min­imized by the fundamental carrier frequency being equal
to final transmitting frequency, modulated directly in the
transmit VCO. Additional harmonic suppression is pro­vided by a low-pass filter consisting of coils L1003 and
L1006, capacitors C1009, C1012, C1020, C1023, and C1030,
resulting in more than 60 dB of harmonic suppression
prior to delivery to the antenna.

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This pulse train is filtered to DC and returned to the var­actor diodes D1001 (HVC358B) and D1002 (HVC355B).
Changes in the level of the DC voltage applied to the var­actor diodes, affecting the reference in the tank circuit of
the VCO according to the phase difference between the
signals derived from the VCO and the TCXO Unit X1001.

The VCO is thus phase-locked to the crystal reference os­cillator. The output of the VCO Q1003 (2SC5231), after
buffering by Q1006 (2SC5005), is applied to the 1st mixer
as described previously.

For transmission, the VCO Q1003 (2SC5231) oscillates
between 150 and 174 MHz according to the programmed
transmit frequency. The remainder of the PLL circuitry is
shared with the receiver. However, the dividing data from
the microprocessor is such that the VCO frequency is at
the actual transmit frequency (rather than offset for IFs,
as in the receiving case). Also, the VCO is modulated by
the speech audio applied to D1005 (HVC350), as described
previously.

Receive and transmit buses select which VCO is made
active by Q1002 and Q1004 (both RT1N441U). TCXO unit
X1001 yields frequency stability of ±2.5 ppm @ –30 °C to
+60 °C.

Push-To-Talk Transmit Activation

The PTT switch S1002 is connected to pin 48 of micropro­cessor Q1013 (M37516F8HP), so that when the PTT switch
is closed, pin 23 of Q1013 (M37516F8HP) goes low. This
signal disables the receiver by disabling the 5 V supply
bus at Q1025 (DTB123EK) to the front-end, FM IF sub­system IC Q1040 (TA31136FN), and receiver VCO circuit-
ry.

At the same time, pin 22 of Q1013 (M37516F8HP) goes
high to activates the transmit 5V supply line at Q1021
(FMW1) and Q1020 (CPH6102) to enable the transmitter.

Circuit Description

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