HYT TM-600 User manual

4

TM-600 Mobile Radio
1
Contents
Revision History ................................................................................................................2
Introduction........................................................................................................................3
Safety Information .............................................................................................................3
Radio Overview..................................................................................................................5
Software Specification ......................................................................................................7
Circuit Description...........................................................................................................17
Semiconductor Data ........................................................................................................22
Component Description ..................................................................................................27
TM-600 Parts List 1 ..........................................................................................................28
Tuning Description ..........................................................................................................92
Terminal Function ..........................................................................................................104
Troubleshooting Flow Chart .........................................................................................107
Disassembly and Reassembly for Repair.................................................................... 111
Exploded View ...............................................................................................................114
TM-600 Parts List 2 ........................................................................................................ 115
Packing ........................................................................................................................... 116
TM-600 PCB View........................................................................................................... 117
TM-600 Block Diagram ..................................................................................................126
TM-600 Schematic Diagram ..........................................................................................127
Specifications ................................................................................................................141

TM-600 Mobile Radio
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Revision History
Version Date Contents Revised
8130M60000000 January, 2007 Initial Release
8130M60000010 March, 2008 The following information is updated/added:
1. New frequency ranges (470-520MHz 350-400MHz
440-470MHz) are added.
2. Tuning Description, Parts List 1, Schematic Diagram and
PCB View are updated.
3. Definition of J503 (further expansion port) is added.
4. Parts List 2 and Exploded View are updated.
5. Function key, tuning item and initial frequency of each
channel are added.
8130M60000020 August, 2009 The following information is updated/added:
1. Parts List 1, Schematic Diagram and PCB View are
updated.
2. Definition of J503 (further expansion port) is updated.
3. Tuning Description is updated.
4. DI and reset circuits are added for U1-U4.

TM-600 Mobile Radio
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Introduction
Manual Scope
This manual is intended for use by experienced technicians familiar with similar types of communication
equipment. It contains all service information required for the equipment and is current as of the
publication date.
Safety Information
The following safety precautions shall always be observed during operation, service and repair of this
equipment.
zThis equipment shall be serviced by qualified technicians only.
zDo not modify the radio for any reason.
zUse only HYT supplied or approved antenna.
zGain of antenna must not exceed 3dBi for VHF or 5.5dBi for UHF.
zMobile antenna Installation: Install the mobile antenna at least 82cm (32 inches) away from your
body, in accordance with the requirements of the antenna manufacturer/supplier.
zTransmit only when people inside and outside the vehicle are at least the minimum distance away
from a properly installed, externally mounted antenna.
zMobile antenna substitution: Don’t substitute HYT supplied or approved antenna, or excessive radio
frequency radiation will result. Please contact your dealer or the manufacturer for further
instructions.
zPlease make sure there’s no stress on the antenna joint during transportation or installation.
zTo avoid electromagnetic interference and/or compatibility conflicts, turn off your radio in any area
where posted notices instruct you to do so. Hospital or health facilities may be using equipment that
is sensitive to external RF energy.
zFor vehicles with an air bag, do not place a radio in the area over an air bag or in the air bag
deployment area.
zTurn off your radio prior to entering any area with explosive and flammable materials.
zDo not expose the radio to direct sunlight over a long time, nor place it close to heating source.

TM-600 Mobile Radio
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▇Operation Guidelines
For vehicles equipped with electronic anti-skid braking systems, electronic ignition systems or electronic
fuel injection systems, interferences may occur during radio transmission. If the foregoing electronic
equipments are installed on your vehicle, please contact your dealer for further assistance to make sure
that radio transmission will not interfere with these equipments.
For radio installation in vehicles fueled by LP gas with LP gas container within interior of the vehicles, the
following precautions are recommended for personal safety.
1. Any space containing radio equipment shall be isolated by a seal from the space in which the LP gas
container and its fittings are located.
2. Remote (outside) fitting connections shall be used.
3. Good ventilation is required for the container space.
▇Installation Guidelines
zVehicle installation: The antenna can be mounted at the center of a vehicle metal roof or trunk lid if
the minimum safe distance is observed.
zDo not mount the mobile radio overhead or on a sidewall unless you take special precautions.
zIf the mobile radio is not properly installed, road shock could bump the radio loose, and the falling
radio could, in some circumstances, cause serious injury to the driver or a passenger. In case of
vehicle accidents, even when properly installed, the radio could break loose and become a
dangerous projectile.

TM-600 Mobile Radio
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Radio Overview
Front Panel View
1) [Volume] Knob
Rotate the knob clockwise to increase the volume, and rotate it counter-clockwise to decrease the
volume.
2) Low Power Indicator
This indicator glows when the radio is at low power.
3) Scan Indicator
This indicator glows when the radio is scanning.
4) 8-segment Numeric LED
Used to display the current channel number, menu, option, etc.
5) [▲]Key
6) [▼]Key
Your dealer can program [▲]/[▼]as shortcuts to various radio features.
7) TX/RX Indicator
This indicator glows red during transmission, and glows green during reception.
8) [Power] Switch
Used to turn the radio on/off.
9) [P2] Key
10) [P1] Key
Your dealer can program [P1]/[P2] as shortcuts to various radio features.
11) Microphone Jack
Used to connect the microphone.

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Rear Panel View
1）15-Pin Connector (for external expansion)
2）External Speaker Jack
Used to connect the external speaker (for the 3.5mm plug only).
Note: Please refer to “Test Cable for Speaker Output” in “Tuning Description” for details.
3）Power Inlet
Used to connect the HYT-authorized DC power cable for input of 13.6V DC power.
4）Antenna Connector
Used to connect the external connector.
Microphone
8-segment Numeric LED Display

TM-600 Mobile Radio
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Software Specification
Frame of Radio Modes
Keypad Entry for Mode Startup
Mode Display Operation Remarks
User Mode Channel No. The radio enters User Mode upon
power-on.
i.e. Conventional Mode
Tuning Mode 0Power on the radio whiling holding
down [P1].
Model Set Mode 0Power on the radio whiling holding
down [P2].
Clone Mode C Power on the radio whiling holding
down [P1]+[P2].
PC Mode No display Connect the mobile radio to PC via
the programming cable, and then
send commands via PC.
PC Mode
Tuning Mode
Conventional Mode
User Mode
Model Set Mode
Clone Mode
Wired Clone Mode
Wireless Clone Mode

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Key Assignment
Your dealer may assign a function to the programmable key ([P1]/[P2], [▲]/[▼]). See the table below for
more details.
Note: "CH Number” in the table below indicates any value within 1~8.
Key Assignment
No. Function
Key Setting Display Remarks
Off CH Number No function
CH Up CH Number Channel up
CH Down CH Number Channel down
MONI A CH Number
MONI A: Monitor
Unmute-Momentary
MONI B CH Number MONI B: Monitor Unmute-Toggle
MONI C (default) CH Number
MONI C: Carrier
Squelch-Momentary
MONI D CH Number MONI D: Carrier Squelch-Toggle
User Selectable
Tone (UST) UST Number (0.-9.) CTCSS/CDCSS signaling
Sel 2-Tone 2-Tone Number (0.-9.) Select 2-Tone.
Sel Tx Power CH Number Switch Tx power.
Scan ●Scan
Add/Delete ●Temporarily add/delete a nuisance
channel.
Reverse CH Number Reverse frequency
Talk Around CH Number Talk around
SEL SQL SQL Number (0.-9.) Select squelch level.
Home CH Home CH Number(1-8) Home channel
Public Address P Public address
Scrambler CH Number Scrambler
Compander CH Number Compander
Emergency Call EmergencyCH
Number (1- 8) Emergency call
HDC Encode Call List Number HDC call
Lone Worker L. or L Lone worker
Whisper R. or R Whisper
AUX A None AUX A
AUX B None AUX B
1 [P1]
Transparent
Transmission Mode CH Number
Enable/disable Transparent
Transmission Mode.
2 [P2] Off CH Number No function

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CH Up CH Number Channel up
CH Down CH Number Channel down
MONI A CH Number
MONI A: Monitor
Unmute-Momentary
MONI B CH Number MONI B: Monitor Unmute-Toggle
MONI C CH Number
MONI C: Carrier
Squelch-Momentary
MONI D CH Number MONI D: Carrier Squelch-Toggle
User Selectable
Tone (UST) UST Number (0.-9.) CTCSS/CDCSS signaling
Sel 2-Tone 2-Tone Number (0.-9.) Select 2-Tone.
Sel Tx Power CH Number Switch Tx power.
Scan (default) ●Scan
Add/Delete ●Temporarily add/delete a nuisance channel.
Reverse CH Number Reverse frequency
Talk Around CH Number Talk around
SEL SQL SQL Number (0.-9.) Select squelch level.
Home CH HomeCH Number (1- 8) Home channel
Public Address P Public address
Scrambler CH Number Scrambler
Compander CH Number Compander
Emergency Call EmergencyCH
Number (1-8) Emergency call
HDC Encode List Number (1.-9.) HDC call
Lone Worker L (off) L . (on) Lone worker
Whisper R (off) R. (on) Whisper
AUX A None AUX A
AUX B None AUX B
Transparent
Transmission Mode CH Number
Enable/disable Transparent
Transmission Mode.
Off CH Number No function
CH Up (default) CH Number Channel up
CH Down CH Number Channel down
MONI A CH Number
MONI A: Monitor
Unmute-Momentary
MONI B CH Number MONI B: Monitor Unmute-Toggle
MONI C CH Number
MONI C: Carrier
Squelch-Momentary
MONI D CH Number MONI D: Carrier Squelch-Toggle
User Selectable
Tone (UST) UST Number (0.-9.) CTCSS/CDCSS signaling
Sel 2-Tone 2-Tone Number (0.-9.) Select 2-Tone.
3
[▲]
Sel Tx Power CH Number Switch Tx power.

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Scan ●Scan
Add/Delete ●Temporarily add/delete a nuisance
channel.
Reverse CH Number Reverse frequency
Talk Around CH Number Talk around
SEL SQL SQL Number (0.-9.) Select squelch level.
Home Channel HomeCH Number (1-8) Home channel
Public Address P Public address
Scrambler CH Number Scrambler
Compander CH Number Compander
Emergency Call Emergency CH
Number (1- 8) Emergency call
HDC Encode Call List Number HDC call
Lone Worker L. or L Lone worker
Whisper R. or R Whisper
AUX A None AUX A
AUX B None AUX B
3
[▲]
Transparent
Transmission Mode CH Number
Enable/disable Transparent
Transmission Mode.
Off CH Number No function
CH Up CH Number Channel up
CH Down (default) CH Number Channel down
MONI A CH Number
MONI A: Monitor
Unmute-Momentary
MONI B CH Number MONI B: Monitor Unmute-Toggle
MONI C CH Number
MONI C: Carrier
Squelch-Momentary
MONI D CH Number MONI D: Carrier Squelch-Toggle
User Selectable
Tone (UST) UST Number (0.-9.) CTCSS/CDCSS signaling
Sel 2-Tone 2-Tone Number (0.-9.) Select 2-Tone.
Sel Tx Power CH Number Switch Tx power.
Scan ●Scan
Add/Delete ●Temporarily add/delete a nuisance
channel.
Reverse CH Number Reverse frequency
Talk Around CH Number Talk around
SEL SQL SQL Number (0.-9.) Select squelch level.
Home Cannel HomeCH Number (1-8) Home channel
Public Address P Public address
Scrambler CH Number Scrambler
Compander CH Number Compander
4
[▼]
Emergency Call Emergency CH
Number (1- 8) Emergency call

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HDC Encode Call List Number HDC call
Lone Worker L. or L Lone worker
Whisper R. or R Whisper
AUX A None AUX A
AUX B None AUX B
4 [▼]
Transparent
Transmission Mode CH Number
Enable/disable Transparent
Transmission Mode.
Hook Check
CH Number
Selected when a remote speaker
microphone is in use.
5
[HOOK
]/[MON
I] Monitor CH Number
Selected when a desktop
microphone is in use.
6
[Volum
e]
Knob Volume Control CH Number Control volume.
PC Mode
After connected with the mobile radio via the programming cable, PC can send data to the radio and
save it in the radio’s EEPROM. In addition, radio programming and tuning are accessible via the
programming software.
1. LED glows green when PC is writing data into the radio, and glows red when PC is reading data
from the radio. After programming is completed, the radio will reset automatically.
2. The following items can be set via the programming software:
1）TX High Power
2）TX Low Power
3）Maximum Frequency Deviation
4）CDCSS Balance
5）CTCSS Deviation (67.0Hz)
6）CTCSS Deviation (151.4Hz)
7）CTCSS Deviation (254.1Hz)
8）CDCSS Deviation
9）DTMF Deviation
10）MSK Deviation
11）Single Tone Deviation
12）RX Sensitivity
13）Squelch On Level (9)
14）Squelch On Level (3)
15）Squelch Off Level (9)
16）Squelch Off Level (3)

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Clone Mode
Data can be transferred from one radio to another through Wired Clone Mode or Wireless Clone Mode.
Wired Clone Mode
1) Power on the source radio while holding down [P1]+[P2]. Then “C” is displayed on the 8-segment
numeric LED. After LED flashes orange twice, the radio enters Wired Clone Mode. However, if Clone
Mode is disabled by your dealer, User Mode will be entered.
2) Press [▲]to switch between Dealer Clone Mode and Factory Clone Mode, with “C” or “C.” displayed
respectively.
3) Dealer Clone Mode (default mode) is different from Factory Clone Mode for the reason that tuning
data and embedded messages will not be cloned in Dealer Clone Mode. However, in Factory Clone
Mode, all data will be cloned.
4) Connect the target radio to the source radio via the programming cable and turn the target radio on.
5) Press [P2] on the source radio to start cloning. The LED on the source radio glows red, and data is
being cloned to the target radio. During the cloning process, the LED on the target radio glows green.
When all data is successfully cloned, the LED on the source radio goes out, and the target radio
automatically enters User Mode. If cloning fails, the LED on the target radio flashes red.
6) Press [P2] on the source radio to return to Clone Mode, with “C” or “C.” on the 8-segment numeric
LED. Repeat the above steps to continue wired cloning.
Wireless Clone Mode
1) Power on the source radio while holding down [P1]+[P2]. Then “C” is displayed on the 8-segment
numeric LED. After LED flashes orange twice, the radio enters Wired Clone Mode. However, if Clone
Mode is disabled by your dealer, User Mode will be entered.
2) Press [P1] to enter Wireless Clone Mode, with “1” displayed on the 8-segment numeric LED. You
can press [P1] again to return to Wired Clone Mode.
3) Press [▲]to switch between Dealer Clone Mode and Factory Clone Mode, with “1” or”1.” displayed
on the 8-segment numeric LED respectively. Press [▼]to select a channel for cloning, and the
channel number is then displayed on the 8-segment numeric LED. “1” indicates that Dealer Clone
Mode is entered, while ”1.” Indicates Factory Clone Mode is entered.
Dealer Clone Mode (default mode) is different from Factory Clone Mode for the reason that tuning
settings and embedded messages will not be cloned in Dealer Clone Mode. However, in Factory
Clone Mode, all data will be cloned.
4) For the target radio, repeat steps 1)-2). Then place the target radio close to the source radio, and
press [P2] on the source radio to start wireless cloning.
5) During cloning, the LED on the source radio glows red, while the LED on the target radio glows
orange.
6) After cloning is completed, the red LED on the source radio goes out. You may repeat the steps
above to continue wireless cloning. When all data is successfully received, the target radio
automatically enters User Mode; otherwise, its LED flashes red.
Note: Clone Mode can be enabled/disabled by your local dealer. Wired Clone Mode is accessible only
when Clone Mode is enabled.

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Tuning Mode
1. For Tuning Mode, operate as follows:
1) Power on the radio while holding down [P1]. The LED flashes red twice, and then the radio enters
Tuning Mode.
2) Use [▲]/[▼]to select a tuning item among 0-9, A-F, with “0.-9.”, “A.-F.” displayed respectively.
3) Sub-item and corresponding display:
i. For tuning items 0-9 and A-B: Press [P2] to enter an item, and use [▲]/ [▼]to adjust the value.
Then press [P2] again to save the value and move to the next item; or press [P1] to return to the
previous item without saving the value.
ii. For tuning items C-F: Press [P2] to enter an item, and press it again to acquire the value
automatically, with “0-6” displayed. Then press [P2] to save the value and move to the next item;
or press [P1] to return to the previous item without saving the value.
Note: 0.: Center frequency; 1.: Low frequency; 2.: High frequency; 3.: Center frequency of medium band;
4.: Center frequency of narrow band; 5.: Low frequency of narrow band; 6.: High frequency of narrow
band; 7: Low-medium frequency; 8: Medium-high frequency.
2. Tuning Items and Display
Tuning
Item
Main
Display
Wideband/
Narrowband Frequency Sub Display Description
Center 0．No signal
Low 1．No signal
TX High
Power
0 High power
W
High 2．No signal
Center 0．No signal; Low Power
Indicator is on.
Low 1．No signal; Low Power
Indicator is on.
TX Low
Power 1 Low power
W
High 2．No signal; Low Power
Indicator is on.
Center 0．No signal
Low 1．No signal
W
High 2．No signal
M Center
3．No signal
Center 4．No signal
Low 5．No signal
Maximum
Frequency
Deviation
2
N
High 6．No signal
Center 0．100Hz square wave
Low 1．100Hz square wave
W
High 2．100Hz square wave
M Center
3．100Hz square wave
CDCSS
Balance 3
N Center
4．100Hz square wave
Center 0．CTCSS: 67.0Hz
Low 1．CTCSS: 67.0Hz
CTCSS
Deviation
4
W
High 2．CTCSS: 67.0Hz

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M Center
3．CTCSS: 67.0Hz
N Center
4．CTCSS: 67.0Hz
Center 0．CTCSS: 151.4Hz
Low 1．CTCSS: 151.4Hz
W
High 2．CTCSS: 151.4Hz
M Center
3．CTCSS: 151.4Hz
5
N Center
4．CTCSS: 151.4Hz
Center 0．CTCSS: 254.1Hz
Low 1．CTCSS: 254.1Hz
W
High 2．CTCSS: 254.1Hz
M Center
3．CTCSS: 254.1Hz
6
N Center
4．CTCSS: 254.1Hz
Center 0．CDCSS: 023N
Low 1．CDCSS: 023N
W
High 2．CDCSS: 023N
M Center
3．CDCSS: 023N
CDCSS
Deviation 7
N Center
4．CDCSS: 023N
Center 0．DTMF: 9
Low 1．DTMF: 9
W
High 2．DTMF: 9
M Center
3．DTMF: 9
DTMF
Deviation 8
N Center
4．DTMF: 9
Center 0．0XAAA…
Low 1．0XAAA…
W
High 2．0XAAA…
M Center
3．0XAAA…
MSK
Deviation 9
N Center
4．0XAAA…
Center 0．1KHz
Low 1．1KHz
W
High 2．1KHz
M Center
3．1KHz
Single
Tone
Deviation
A
N Center
4．1KHz
- Low
1．No signal; SQL off
- Low-medium 7．No signal; SQL off
- Center
0．No signal; SQL off
- Medium-high 8．No signal; SQL off
Rx
Sensitivity B
- High 2．No signal; SQL off
Center 0．No signal
Low 1．No signal
SQL 9
W High 2．No signal
Squelch
On Level
C
SQL 9
M Center 3．No signal

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Center 4．No signal
Low 5．No signal
SQL 9
N High 6．No signal
Center 0．No signal
Low 1．No signal
SQL 9
W High 2．No signal
SQL 9
M Center 3．No signal
Center 4．No signal
Low 5．No signal
D
SQL 9
N High 6．No signal
Center 0．No signal
Low 1．No signal
SQL 9
W High 2．No signal
SQL 9
M Center 3．No signal
Center 4．No signal
Low 5．No signal
E
SQL 9
N High 6．No signal
Center 0．No signal
Low 1．No signal
SQL 3
W High 2．No signal
SQL 3
M Center 3．No signal
Center 4．No signal
Low 5．No signal
Squelch
Off Level
F
SQL 3
N High 6．No signal
Model Set Mode
1. Power on the radio while holding [P2]. After the LED flashes green twice, the radio enters Model Set
Mode. The selected frequency range will be displayed on the 8-segment numeric LED.
2. Press [▲]/[▼]to select a frequency range (0-5).
3. Press [P2] to confirm the selection. Then the LED glows orange and the radio starts to reset. After
reset, the radio enters User Mode.
Note:
1. Once [P2] is pressed to confirm a new frequency range, the previously stored channel information
(such as frequency, CTCSS/CDCSS, channel function settings) will be cleared, and some functions
will also be changed. Therefore, do not make this operation unless it’s very necessary (e.g. when
EEPROM is replaced).
2. The table below lists frequency range of each model and initial frequency of each channel after
frequency range is set.

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Note: L: lowest frequency; H: highest frequency; C: center frequency
Frequency
range RX/TX 1 ( C ) 2 ( L ) 3 ( H ) 4 5 6 7 8
RX(MHz) 155.15 136.15 173.85 145.55 164.55 155.00 155.20 155.40
0(V) TX(MHz) 155.00 136.00 174.00 145.50 164.50 155.00 155.20 155.40
RX(MHz) 435.15 400.15 469.85 417.55 452.55 435.00 435.20 435.40
1(U1) TX(MHz) 435.00 400.00 470.00 417.50 452.50 435.00 435.20 435.40
RX(MHz) 475.15 450.15 499.85 462.55 487.55 475.00 475.20 475.40
2(U2) TX(MHz) 475.00 450.00 500.00 462.50 487.50 475.00 475.20 475.40
RX(MHz) 495.15 470.15 519.85 482.55 507.55 495.00 495.20 495.40
3(U3) TX(MHz) 495.00 470.00 520.00 482.50 507.50 495.00 495.20 495.40
RX(MHz) 375.15 350.15 399.85 362.55 387.55 375.00 375.20 375.40
4(U4) TX(MHz) 375.00 350.00 400.00 362.50 387.50 375.00 375.20 375.40
RX(MHz) 455.15 440.15 469.85 447.55 462.55 455.00 455.20 455.40
5(U5) TX(MHz) 455.00 440.00 470.00 447.50 462.50 455.00 455.20 455.40
TM-600 VHF: 136-174MHz;
TM-600 U1: 400-470MHz;
TM-600 U2: 450-500MHz;
TM-600 U3: 470-520MHz;
TM-600 U4: 350-400MHz;
TM-600 U5: 440-470MHz;
CH 1 2 3 4 5 6 7 8
RX OFF OFF OFF OFF CTS67.0HZ DI454 151.4 DI454CTCSS
CDCSS TX OFF OFF OFF OFF CTS67.0HZ DI454 151.4 DI454
PWR TX H H H L L L L L
CH
NAME
CH 1
Wide
CH 2
Wide
CH 3
Wide
CH 4
N
CH 5
Wide
CH 6
Wide
CH 7
N
CH 8
N

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17
Circuit Description
Frequency Configuration
The receiver utilizes double conversion superheterodyne. The first IF is 49.95MHz and the second IF is
450KHz. The first local oscillator signal is supplied by the PLL circuit, while the second local oscillator
signal (50.4MHz) is generated from the frequency tripling of TCXO (16.8MHz). The PLL circuit generates
the frequencies required for transmission. See Fig.1.
Frequency Range VHF: 136MHz-174MHz
UHF: 400MHz-470MHz;
450MHz-500MHz;
470MHz-520MHz;
350MHz-400MHz;
440MHz-470MHz;
Receiver Circuit
The receiver section configuration is shown as Fig. 1.
Fig. 1 Receiver Circuit
1. RF AMP BPF
It consists of the front-stage BPF (LC resonant circuit where D107, D108 and D109 are located) and RF
amplifier (Q111) and the final-stage BPF(D110 and D111). The bandpass frequency range is the
frequency range of the radio. The signals are filtered by the BPF to remove unwanted signals before
going to the first mixer.
2. The First Mixer
The signal from the BPF is mixed with the first local oscillator signal from the PLL circuit in the first mixer
(Q112) to generate the first IF signal (49.95MHz). The first IF signal then feeds through the crystal filter
(IF200) to further remove spurious signals.

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18
3. IF Amplifier
The first IF signal is amplified by Q113 and then enters IC102 (TA31136FN), where the signal is mixed
with the second local oscillator signal (50.4MHz) to generate the second IF signal (450KHz). The second
IF signal then feeds through a ceramic filter (N: CF202; W: CF203) to remove unwanted signal. Finally
the resulting signal is processed by IC102 and output from Pin 9 as the audio signal.
4. Audio Amplifier
The Rx audio signal from IC102 is amplified and filtered by IC402, and then enters IC401 for further
amplification (the Rx signalling is obtained and input into CPU for decoding). The processed signal
passes through Q406 (AF MUTE) and is amplified by IC405. Then the amplified signal feeds to K301
(volume control) and Q511 (SP MUTE) before entering audio amplifier (IC511). Finally the audio signal is
output to drive the speaker.
5. Squelch Circuit
Some Rx audio signals from IC102 go back to IC102 via its Pin8, and are amplified, filtered and rectified
by IC102 to produce an SQL level. The SQL level is then compared with the existing reference level in
CPU (IC502) to generate a level to control AF MUTE and SP MUTE, and to determine whether to output
audio from the speaker by controlling Q406 and Q511.
Transmitter Circuit
The transmitter circuit is composed of MIC circuit, modulation circuit, RF driver, final-stage power
amplifier circuit and APC circuit.
Fig. 2 Transmitter Circuit
1. MIC and Modulation circuit
The audio signal from MIC is amplified by IC405. The resulting signal is then amplified, pre-emphasized
and encoded by IC401. Before the audio signal enters VCO, signaling is added. Then the signal with
signaling added goes to VCO for modulation.

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19
2. RF Driver and Final-stage Power Amplifier Circuit
The TX-RF signal from Q703 in the VCO circuit is amplified by Q101, Q110 and Q109, and goes to the
final-stage amplifier (IC101) for further amplification. Then the amplified signal enters LPF and is
transmitted from the antenna.
3. APC
The APC is used to keep the power output at a constant preset value. D101 and D102 transform the
signal from the detector to DC voltage, which is then compared with the reference voltage from CPU in
IC104 and output as DC control voltage. The DC control voltage controls the output power by controlling
the grid of IC101.
4. DI Balance Modulation Circuit
This circuit allows you to change signal amplitude by adjusting VR802 manually, and realize perfect
modulation of external data signal (DI), without any distortion. Thus, the potential for further expansion is
greatly enhanced.
PLL Circuit
PLL circuit generates the first local oscillator signal for reception and the RF signal for transmission. PLL
circuit consists of TX frequency oscillator (Q701), RX frequency oscillator (Q702), buffer amplifier (Q703),
RF amplifier (Q102), PLL IC (IC801), LPF and TX/RX VCO control switch (Q704, Q706).
In Tx mode, IC120 transmits the frequency data to PLL IC and drives PLL IC. Q704 is turned on to
activate TX VCO. The output signal is amplified by Q703, Q102, and then divided by PLL IC into 2.5KHz,
5KHz or 6.25KHz signal. The divided signal is compared with 2.5KHz, 5KHz or 6.25KHz reference signal
from the 16.8MHz crystal oscillator (2.5 PPM frequency stability) in the phase comparator. The frequency
control voltage from the phase comparator is sent to TX VCO after passing through LPF (Q802, Q803).
In the meantime, modulation signal (TX) is passed to TX VCO for frequency modulation.
The working principle in Rx mode is similar to that in Tx mode.
Fig. 3 PLL Circuit