Yaesu vx 160 schematic

VHF FM Transceiver

VX-160V/-180V

Service Manual

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.

International Division

8350 N.W. 52nd Terrace, Suite 201, Miami, FL 33166, 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-160V VX-180V

Introduction

This manual provides technical information necessary for servicing the VX-160V and VX-180V 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

Operating Manual Reprint ........................... 2

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

Specifications................................................... 7

Exploded View & Miscellaneous Parts ...... 8

Block Diagram.................................................9

Circuit Description ................................10

Alignment ................................................12

Board Unit (

MAIN Unit............................................................... 17

Schematics, Layouts & Parts

)

Operating Manual Reprint

Controls & Connectors Before You Begin

LED Indicator

Glows Green Monitor on Blinking Green Busy Channel (or SQL off) Glows Red Transmitting Blinking Red Battery Voltage is low Blinking Yellow Receiving a Selective Call

Antenna

Push To Talk (

PTT) Switch

Monitor Button

Microphone

Battery Pack Latch

CH (Channel) Selector

VOL/PWR Knob

MIC/SP Jack

(

External Mic/Earphone

Speaker

LCD (VX-180)

Soft KEY (VX-180)

Display Icons & Indicators (VX-180 Only)

Battery Pack Installation and Removal

r To install the battery, hold the transceiver with your

left hand, so your palm is over the speaker and your thumb is on the top of the belt clip. Insert the battery pack into the battery compartment on the back of the radio while tilting the Belt Clip outward, then close the Battery Pack Latch until it locks in place with a “Click.”

)

r To remove the battery, turn the radio off and remove

any protective cases. Open the Battery Pack latch on the bottom of the radio, then slide the battery downward and out from the radio while holding the Belt Clip.

Caution!

Do not attempt to open any of the rechargeable NiCd packs, as they could explode if accidentally shortcircuited.

This indicator confirms that DUAL WATCH is active.

This icon is the “Low Battery” indicator, which appears when the battery voltage becomes too low for proper operation.

This indicator confirms that DUAL 2-TONE DECODE is active.

This indicator confirms that this channel will be skipped during scan.

8 Character Alpha-numeric Invertible Display

Low Battery Indication

r As the battery discharges during use, the voltage gradu-

ally becomes lower. When the battery voltage reaches

6.3 volts, substitute a freshly charged battery and recharge the depleted pack. The TX/BUSY indicator on the top of the radio will blink red (on the VX-180, the “ ” icon will appear on the LCD) when the battery voltage is low.

r Avoid recharging Ni-Cd batteries often with little use

between charges, as this can degrade the charge capacity. We recommend that you carry an extra, fullycharged pack with you so the operational battery may be used until depletion (this “deep cycling” technique promotes better long-term battery capacity).

Operation

Operating Manual Reprint

Preliminary Steps

r Install a charged battery pack onto the transceiver, as

described previously. r Screw the supplied antenna onto the Antenna jack.

Never attempt to operate this transceiver without an

antenna connected. r If you have a Speaker/Microphone, we recommend that

it not be connected until you are familiar with the ba-

sic operation of the VX-160/-180.

Operation Quick Start

r Turn the top panel’s VOL/

PWR knob clockwise to turn

on the radio on.

r Turn the top panel’s CH selec-

tor knob to choose the desired

operating channel.

r Rotate the VOL/PWR knob to

set the volume level. If no sig-

nal is present, press and hold

in the MONITOR key (the

lower button on the left side)

for more than 1 seconds; back-

ground noise will now be heard, and you may use this

to set the VOL/PWR knob for the desired audio level.

r Press and hold in the MONI-

TOR key for more than 1 sec-

onds (or press the MONITOR key twice) to quiet the noise and resume normal (quiet) monitoring.

r To transmit, press and hold in

the PTT switch. Speak into the microphone area of the front panel grille (lower left-hand corner) in a normal voice level. To return to the Receive mode, release the PTT switch.

r If a Speaker/Microphone is available, remove the plas-

tic cap and its two mounting screws from the right side of the transceiver, then insert the plug from the Speaker/ Microphone into the MIC/SP jack; secure the plug using the screws supplied with the Speaker/Microphone. Hold the speaker grille up next to your ear while receiving. To transmit, press the PTT switch on the Speaker/Microphone, just as you would on the main transceiver’s body.

Note:Save the original plastic cap and its mounting

screws. They should be re-installed when not using the Speaker/Microphone.

Key Functions

The VX-180 provides programmable [A], [B], and [C] function keys, and both the VX-160 and VX-180 provide programmable MONITOR keys. These “Soft” keys functions can be customized (set to other functions), via programming by your VERTEX STANDARD dealer, to meet your communications/network requirements. Some features may require the purchase and installation of optional internal accessories. The possible Soft key programming features are illustrated at the right, and their functions are explained in the next chapter. For further details, contact your VERTEX STANDARD dealer. For future reference, check the box next to each function that has been assigned to the Soft key on your particular radio, and keep it handy.

Function

None Monitor Low Power Lock* Lamp* Channel Up* Channel Down* Scan Follow-me Scan Dual Watch Talk Around Add/Del* Call/Reset Speed Dial TX Save Off

* VX-180 only

Soft Key

[A] [B] [C]

MONITOR key

Operating Manual Reprint

Description of Operating Functions

Monitor

Press the assigned Soft key momentarily to override (disable) the Tone squelch. Background noise or incoming signals will now be heard whether or not a matching tone is present on the signal). Press and hold in the assigned Soft key for more than 1 seconds to override both the Noise and Tone squelch. Again press and hold in the assigned Soft key for more than 1 seconds (or press the assigned Soft key twice) to resume normal (quiet) Noise and Tone squelch action.

Low Power

Press the assigned Soft key to set the radio's transmitter to the “Low Power” mode, thus extending battery life. Press the assigned Soft key again to return to “High Power” operation when in difficult terrain.

Lock

Press the assigned Soft key to lock the Soft keys (except Lock and Monitor key); thus, the [A], [B], [C], and MONI- TOR keys can be disabled to prevent radio settings from

being disturbed.

Lamp

Press the assigned Soft key to illuminate the LCD for five seconds.

Channel Up

Press the assigned Soft key to switch to a higher operating channel number.

Channel Down

Press the assigned Soft key to switch to a lower operating channel number.

Scan

The Scanning feature is used to monitor multiple channels programmed into the transceiver. While scanning, the radio will check each channel for the presence of a signal, and will stop on a channel if a signal is present. r To activate scanning:

Press the assigned Soft key. The scanner will search the channels, looking for active ones; it will pause each time it finds a channel on which someone is speaking.

r To stop scanning:

Press the assigned Soft key.

Operation will revert to the channel to which the CH knob is set.

Follow-Me Scan

“Follow-Me” Scan feature checks a User-assigned Priority Channel regularly as you scan the other channels. Thus, if only Channels 1, 3, and 5 (of the 8 available channels) are designated for “Scanning,” the user may nonetheless assign Channel as the “User-assigned” Priority Channel via the “Follow-Me” feature. Press the assigned Soft key to activate “Follow-Me” scanning, then turn the CH selector knob to the channel which you want to designate as the “User-Assigned Priority Channel”. When the scanner stops on an “active” channel, the User-assigned Priority Channel will automatically be checked every few seconds.

Dual Watch

The Dual Watch feature is similar to the Scan feature, except that only two channels are monitored: the current operating channel, and the “Priority” channel. r To activate Dual Watch:

Press the assigned Soft key. The scanner will search the two channels; it will pause each time it finds a channel on which someone is speaking.

r To stop Dual Watch:

Press the assigned Soft key. Operation will revert to the channel to which the CH knob is set.

Talk Around

Press the assigned Soft to activate the Talk Around feature when you are operating on duplex channel systems (separate receive and transmit frequencies, utilizing a “repeater” station). The Talk Around feature allows you to bypass the repeater station and talk directly to a station that is nearby. This feature has no effect when you are operating on “Simplex” channels, where the receive and transmit frequencies are already the same. Note that your dealer may have made provision for “Talk Around” channels by programming “repeater” and “Talk Around” frequencies on two adjacent channels. If so, the key may be used for one of the other Pre-Programmed Functions.

Add/Del

The Add/Del feature allows the user to arrange a custom Scan. Press the assigned Soft key to delete/restore the current channel to/from your scanning list. When you delete a current channel, “SKIP” will appear on the LCD after pressing the Soft key. When you restore a current channel, “SKIP” indicator on the LCD will turn off.

Operating Manual Reprint

Description of Operating Functions

Call/Reset

When the 2-tone selective calling unit is installed, press the assigned Soft key to silence the receiver and reset for another call, when a communication is finished.

Speed Dial

Your Dealer may have pre-programmed Auto-Dial telephone number memories into your radio. To dial a number, just press the Dealer-assigned Soft key for Speed Dialing. The DTMF tones sent during the dialing sequence will be heard in the speaker.

Accessories & Options

FNB-64 7.2 V 700 mAh Ni-Cd Battery FNB-V57 7.2 V 1100 mAh Ni-Cd Battery FBA-25 Alkaline Battery Case NC-77B 120 VAC Overnight Desktop Charger NC-77C 230-240 VAC Overnight Desktop Charger VAC-800 Desktop Rapid Charger VAC-6800 6-unit Multi Charger MH-45B4B Speaker/Microphone MH-37A4B Earpiece Microphone VC-25 VOX Headset VCM-1 Mobile Mounting Bracket (for VAC-800) LCC-160/S Leather Case (for VX-160) LCC-180/S Leather Case (for VX-180) CT-42 PC Programming Cable CT-27 Radio to Radio Programming Cable CE44 Programming Software

TX Save Off

Press the assigned Soft key to disable the Transmit Battery Saver, if you are operating in a location where high power is almost always needed. The Transmit Battery Saver helps extend battery life by reducing transmit power when a very strong signal from an apparently nearby station is being received. Under some circumstances, though, your hand-held radio may not be heard well at the other end of the communication path, and high power may be necessary at all times.

Cloning

The VX-160/-180 includes a convenient “Cloning” feature, which allows the programming data from one transceiver to be transferred to another VX-160/-180. Here is the procedure for Cloning one radio's data to another.

1. Turn both transceivers 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. Press and hold in the PTT and MONITOR switches (just below the PTT switch) while turning the transceiver on. Do this for both transceivers (the order of the switch-on does not matter). “CLONE” will appear on the displays (for the VX-180) of both transceivers when Clone mode is successfully activated in this step; in the case of the VX-160, no change will be observed at this point.

5. On the Destination transceiver, press the MONITOR switch. “LOADING” will appear on the LCD (for VX- 180; for VX-160, the TX/BUSY indicator on the top of the radio will glow Green).

6. Press the PTT switch on the source transceiver; “SEND-

ING” will appear on the Source transceiver (for VX180; for VX-160, the TX/BUSY indicator on the top

of the radio will glow Red), and the data will be transferred.

7. If there is a problem during the cloning process, “ER-

ROR” will appear on the LCD (for VX-180; for VX- 160, the TX/BUSY indicator on the top of the radio

will blink Red); check your cable connections and battery voltage, and try again.

8. If the data transfer is successful, the display will re-

turn to “CLONE” (for VX-180; for VX-160, the TX/ BUSY indicator on the top of the radio will turn off). Turn both transceivers off and disconnect the CT-27 cable. You can then turn the transceivers back on, and begin normal operation.

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

Optional Cloning Cable CT-27

Specifications

GENERAL Specifications

Frequency Range (MHz): 134 - 160 (A)

148 - 174 (C)

Number of Channels: 16 channels Channel Spacing: 12.5 / 25 kHz (15 / 30 kHz) PLL Steps 2.5 / 6.25 kHz Power Supply voltage: 7.5 VDC ± 20% Operating Temperature Range: –22°F to +140°F (–30°C to +60°C) Frequency Stability: ±2.5 ppm Dimensions (WHD): 2.3" (W) x 4.7" (H) x 1.2" (D) (58 x 120 x 31 mm) Weight (approx.): 0.81 lb. (365 g) w/FNB-64

RECEIVER Specifications (Measurements made per EIA standard TIA/EIA-603)

Sensitivity

EIA 12 dB SINAD : 0.20 µV 20 dB Quieting : 0.30 µV

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, 5% THD

TRANSMITTER Specifications (Measurements made per EIA standard TIA/EIA-603)

Power output: 5.0 / 1.0 W Modulation: 16K0F3E, 11K0F3E 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.

Exploded View & Miscellaneous Parts

RA029600A (Lot. 17~)

RA0173500 CAP

R6147510 RING NUT (x 2 pcs)

RA0296100 VOLUME KNOB

RA029620A (Lot. 3~) RA0296200 (Lot. 1~) KNOB (CH)

RA0309800 (Lot. 20~) MYLAR SHEET (SP)

RA0334900A REFLECTOR SHEET (VX-180)

RA0294800 INTER CONNECTOR (VX-180)

RA0107000 TERMINAL PLATE R

RA010340A TERMINAL HOLDER

RA0296000 (Lot. 1~) FRONT CASE ASSY (VX-160)

RA0210600 RUBBER PACKING (x 2 pcs)

M4090151A (Lot. 10~) M4090151 (Lot. 1~) SPEAKER

RA0294200 PTT KNOB

RA0294400 LCD HOLDER (VX-180)

G6090139 LCD (VX-180)

RA029450A (Lot. 10~) RA0294500 LIGHT GUIDE (VX-180)

RA0110200

HOLDER RUBBER

REF. VXSTD P/N Description Qty.

MAIN Unit

À U44104002 TAPTITE SCREW M2X4NI 10

U44104002

(VX-180U)

TAPTITE SCREW M2X4NI 2

Â U20206007 BINDING HEAD SCREW M2.6X6B 2 Ã U24110002 TAPTITE SCREW M2X10NI 2 Ä U02206007 SEMS SCREW SM2.6X6B 2 Å U00103002 PAN HEAD SCREW M2X3NI 1

RA0210900 WINDOW

RA029590B (Lot. 17~) RA0295900 (Lot. 1~) FRONT CASE ASSY (VX-180)

RA0293900 RUBBER KNOB

RA0123500 LATCH NAIL B

TERMINAL PLATE L

CP7064001 BELT CLIP ASSY

RA0294300 (Lot. 1~) RA029430A (Lot. 4~) RUBBER PACKING

RA029310D (Lot. 26~) RA029310C (Lot. 20~) RA029310B (Lot. 11~) RA029310A (Lot. 3~) RA0293100 REAR CASE ASSY (w/SMA CONNECTOR, TERMINAL PLATE L, PAN HEAD SCREW M2X3NI)

CAUTION

The mic element must be desoldered and removed from the PCB on order to reinstall its protective rubber cover.

Therefore, be careful not to remove this cover unless mic element replacement is necessary.

ÁÀ

Block Diagram

Circuit Description

Receive Signal Path

Incoming RF from the antenna jack is delivered to the RF Unit and passes through a low-pass filter consisting of coils L1001, L1002, and L1031, capacitors C1004, C1005, C1008, C1010, C1014, C1016, and C1221, and antenna switching diode D1003 (RLS135 TE-17).

Signals within the frequency range of the transceiver enter a varactor-tuned band-pass filter consisting of coils L1010 and L1011, capacitors C1044, C1046, C1060, C1065, and C1068, and diodes D1011 (HVC358B), D1012 (HVC358B), D1013 (HVC358B), and D1014 (HVC358B), then are amplified by Q1012 (2SC5006- T1) and enter a varactor-tuned band-pass filter consisting of coils L1017 and L1021, capacitors C1084, C1086, C1095, and C1097, and diodes D1018 (HVC358B) and D1019 (HVC358B), before mixing by first mixer Q1026 (SGM2016AM-T7).

Buffered output from the VCO is amplified by Q1007 (2SC5005-T1) to provide a pure first local signal between 190.25 and 218.25 MHz for injection to the first mixer. The 44.25 MHz first mixer product then passes through monolithic crystal filter XF1002 (HDF0042, 5.5 kHz BW) to strip away unwanted mixer products, and the IF signal is then amplified by Q1033 (2SC4215Y TE85R).

The amplified first IF signal is applied to FM IF subsystem IC Q1037 (TA31136FN-EL), which contains the second mixer, second local oscillator, limiter amplifier, noise amplifier, and RSSI amplifier.

The second local signal is produced from the PLL reference/second local oscillator of 14.60 MHz crystal X1001. The 14.60 MHz reference signal is tripled by Q1036, capacitor C1209, and coil L1029, and the resulting 43.8 MHz second local signal is then delivered to the mixer section of Q1037, which produces the 450 kHz second IF when mixed with the first IF signal.

The second IF then passes through ceramic filter CF1001 (ALFYM450G=K on “Narrow” channels) or CF1002 (ALFYM450F=K on “Wide” channels) to strip away all but the desired signal, and then is applied to the limiter amplifier in Q1037, which removes amplitude variations in the 450 kHz IF, before detection of the speech by the ceramic discriminator, CD1001 (CDBC450CX24).

Detected audio from Q1037 is applied to the audio high-pass filter, and then passes via the volume control to the audio amplifier Q1039 (NJM2070M-TE2), which provides up to 1/2 Watt to the optional headphone jack or a 4-ohm loudspeaker.

Squelch Control

The squelch circuitry consists of a noise amplifier and

band-pass filter within Q1037, and noise detector D1018 (1SS355 TE-17).

When no carrier is received, noise at the output of the detector stage in Q1037 is amplified and band-pass filtered by the noise amplifier section of Q1037 and the network between pins 7 and 8, and then is rectified by D1028.

The resulting DC squelch control voltage is passed to pin 37 of the microprocessor Q1014 (M37516E6HP). If no carrier is received, this signal causes pin 24 of Q1014 to go high and pin 20 to go high. Pin 24 signals Q1060 (RT1P441U-T11-1) to disable the supply voltage to the audio amplifier Q1039, while pin 20 holds the green (Busy) half of the LED off, when pin 24 is high and pin 20 is high.

Thus, the microprocessor blocks output from the audio amplifier, and silences the receiver, while no signal is being received (and during transmission, as well).

When a carrier appears at the discriminator, noise is removed from the output, causing pin 37 of Q1014 to go low and the microprocessor to activate the “Busy” LED via Q1014.

The microprocessor then checks for CTCSS or CDCSS code squelch information, if enabled. If not transmitting and CTCSS or CDCSS is not activated, or if the received tone or code matches that programmed, audio is allowed to pass through the audio amplifier Q1039 (NJM2070M TE2) to the loudspeaker by the enabling of the supply voltage to it via Q1037.

Transmit Signal Path

Speech input from the microphone is amplified by Q1017 (NJM2902V TE1); and R1054, the audio is amplified in another section of Q1017.

The processed audio may then be mixed with a CTCSS tone generated by Q1014 (M37516E6HP) for frequency modulation of the PLL carrier (up to ±5 kHz from the unmodulated carrier) at the transmitting frequency.

If a CDCSS code is enabled for transmission, the code is generated by microprocessor Q1014 (M37516E6HP) and delivered to D1004 (HVC350B TRF) for CDCSS modulating.

The modulated signal from the VCO Q1002 (2SC5231C8-TL) is buffered by Q1007 (2SC5005-T1). The low-level transmit signal then passes through the T/ R switching diode D1016 (DAN235E-TL) to driver amplifiers Q1015 (2SC5227-4-TB) and Q1016 (2SK2596BXTL), then the amplified transmit signal is applied to the final amplifier Q1024 (2SK2974-T11), which delivers up to 5 watts of output power.

The transmit signal then passes through the antenna switch D1003 (RLS135 TE-11) and is low-pass filtered, to suppress harmonic spurious radiation, before delivery to the antenna.

after pre-emphasis by C1066

Circuit Description

Automatic Transmit Power Control

Current from the final amplifier is sampled by R1108, R1115, and R1125, and is rectified by Q1057 (IMZ2A T108). The resulting DC is fed back through Q1032 (FMW1 T98) to the drive amplifier Q1016 and final amplifier Q1024, for control of the power output. The microprocessor selects “High” or “Low” power levels.

Transmit Inhibit

When the transmit PLL is unlocked, pin 7 of PLL chip

Q1005 goes to a logic “Low,” and unlock detector Q1056 (2SA1586Y TE85R) goes to a logic “High.” The resulting DC unlock control voltage is passed to pin 14 of the microprocessor, Q1014. While the transmit PLL is unlocked, pin 22 of Q1014 remains high, which then turns off Q1029 (CPH6102-TL) and the Automatic Power Controller Q1032 (FMW1 T98) to disable the supply voltage to the drive amplifiers Q1015/Q1016 and final amplifier Q1024, thereby disabling the transmitter.

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 L1001, L1002, and L1031 plus capacitors C1004, C1005, C1008, C1010, C1014, C1016, and C1221, resulting in more than 60 dB of harmonic suppression prior to delivery of the RF signal to the antenna.

PLL Frequency Synthesizer

The PLL circuitry on the Main Unit consists of VCO Q1002 (2SC5231C8-TL), VCO buffer Q1007 (2SC5005), and PLL subsystem IC Q1005 (MB15A02PFV1-G-BND-EF), which contains a reference divider, serial-to-parallel data latch, programmable divider, phase comparator, and charge pump.

Frequency stability is maintained by temperature compensating thermistor TH1004. The output from TH1004 is applied to pin 39 of Q1014. Q1014 outputs thermal data to D/A converter Q1052 (M62364FP 600D), which produces a DC voltage corresponding to the thermal data. The resulting DC voltage is applied to varactor diode D1004 (HVC350B TRF) to stabilize the 14.60 MHz Reference Frequency.

While receiving, VCO Q1002 oscillates between

190.25 and 218.25 MHz according to the transceiver version and the programmed receiving frequency. The VCO output is buffered by Q1007, then applied to the prescaler section of Q1005. There the VCO signal is divided by 64 or 65, according to a control signal from the data latch section of Q1005, before being sent to the programmable divider section of Q1005.

The data latch section of Q1005 also receives serial dividing data from the microprocessor, Q1014, 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 or

3.125 kHz derivative of the current VCO frequency.

Meanwhile, the reference divider section of Q1005 divides the 14.60 MHz crystal reference (from the reference oscillator, Q1022) by 5840 (or 4672) to produce the

2.5 kHz (or 3.125 kHz) loop references (respectively).

The 2.5 kHz (or 3.125 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 Q1004, which produces a pulsed output with pulse duration depending on the phase difference between the input signals.

This pulse train is filtered to DC and returned to the varactor D1037 (HVC358B) and D1042 (HVC355B). Changes in the level of the DC voltage are applied to the varactor, affecting the reference in the tank circuit of the VCO according to the phase difference between the signals derived from the VCO and the crystal reference oscillator.

The VCO is thus phase-locked to the crystal reference oscillator. The output of the VCO Q1002, after buffering by Q1007, is applied to the first mixer as described previously.

For transmission, the VCO Q1002 oscillates between 146 and 174 MHz according to the model version and 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 (1SV229 TPH3), as described previously.

Receive and transmit buses select which VCO is made active, using Q1059 (RT1N441U-T11-1) and Q1059 (RT1P441U-T11-1).

Miscellaneous Circuits

Push-To-Talk Transmit Activation

The PTT switch on the microphone is connected to pin 48 of microprocessor Q1014, so that when the PTT switch is closed, pin 23 of Q1014 goes low. This signal disables the receiver by disabling the 5 V supply bus at Q1036 (DTB123EK T146) to the front-end, FM IF subsystem IC Q1037, and the receiver VCO circuitry.

At the same time, Q1027 (FMW1 T98) and Q1029 (CPH6102-TL) activate the transmit 5V supply line to enable the transmitter.

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