Kenwood TK-7108 Service Manual
VHF FM TRANSCEIVER
TK-7108
SERVICE MANUAL
M VERSION
Cabinet
(A01-2178-02)
Front glass
(B10-2668-03)
© 2002-7 PRINTED IN JAPAN
B51-8636-00 (S) PDF
Panel assy
(A62-0942-03)
Key top
(K29-9065-01)
TK-7108
CONTENTS / GENERAL
CONTENTS GENERAL
GENERAL .................................................. 2
OPERATING FEATURES .......................... 4
REALIGNMENT ......................................... 7
DISASSEMBLY FOR REPAIR ................... 9
CIRCUIT DESCRIPTION .......................... 10
SEMICONDUCTOR DATA ...................... 15
COMPONENTS DESCRIPTION .............. 16
PARTS LIST ............................................. 18
EXPLODED VIEW ..................................... 24
PACKING .................................................. 25
ADJUSTMENT ......................................... 26
PC BOARD
DISPLAY UNIT (X54-3340-20) ............. 31
TX-RX UNIT (X57-6293-01) ................. 33
SCHEMATIC DIAGRAM ........................... 39
BLOCK DIAGRAM .................................... 43
LEVEL DIAGRAM ..................................... 45
TERMINAL FUNCTION ............................ 47
SPECIFICATIONS .................. BACK COVER
INTRODUCTION
SCOPE OF THIS MANUAL
This manual is intended for use by experienced technicians familiar with similar types of commercial grade communications equipment. It contains all required service information for the equipment and is current as of this publication date. Changes which may occur after publication are
covered by either Service Bulletins or Manual Revisions,
which are issued as required.
ORDERING REPLACEMENT PARTS
When ordering replacement parts or equipment information, the full part identification number should be included.
This applies to all parts : components, kits, and chassis. If
the part number is not known, include the chassis or kit
number of which it is a part and a sufficient description of
the required component for proper identification.
PERSONNEL SAFETY
The following precautions are recommended for personnel safety :
•DONOT transmit if someone is within two feet (0.6
meter) of the antenna.
•DONOT transmit until all RF connectors are secure and
any open connectors are properly terminated.
• SHUT this equipment when near electrical blasting caps
or while in an explosive atmosphere.
• All equipment should be properly grounded before
power-up for safe operation.
• This equipment should be serviced by only qualified tech-
nicians.
PRE-INSTALLATION CONSIDERNATIONS
1. UNPACKING
Unpack the radio from its shipping container and check
for accessory items. If any item is missing, please contact
KENWOOD immediately.
2. LICENSING REQUIREMENTS
Federal regulations require a station license for each radio installation (mobile or base) be obtained by the equipment owner. The licensee is responsible for ensuring transmitter power, frequency, and deviation are within the limits
permitted by the station license.
Transmitter adjustments may be performed only by a licensed technician holding an FCC first, second or general
class commercial radiotelephone operator’s license. There
is no license required to install or operate the radio.
2
GENERAL
TK-7108
3. PRE-INSTALLATION CHECKOUT
3-1. Introduction
Each radio is adjusted and tested before shipment. However, it is recommended that receiver and transmitter operation be checked for proper operation before installation.
3-2. Testing
The radio should be tested complete with all cabling and
accessories as they will be connected in the final installation.
Transmitter frequency, deviation, and power output should
be checked, as should receiver sensitivity, squelch operation, and audio output. Signalling equipment operation
should be verified.
4. PLANNING THE INSTALLATION
4-1. General
Inspect the vehicle and determine how and where the
radio antenna and accessories will be mounted.
Plan cable runs for protection against pinching or crushing
wiring, and radio installation to prevent overheating.
4-2. Antenna
The favored location for an antenna is in the center of a
large, flat conductive area, usually at the roof center. The
trunk lid is preferred, bond the trunk lid and vehicle chassis
using ground straps to ensure the lid is at chassis ground.
5. INSTALLATION PLANNING – CONTROL STATIONS
5-1. Antenna system
Control station. The antenna system selection depends
on many factors and is beyond the scope of this manual.
Your KENWOOD dealer can help you select an antenna system that will best serve your particular needs.
5-2. Radio location
Select a convenient location for your control station radio
which is as close as practical to the antenna cable entry
point. Secondly, use your system’s power supply (which
supplies the voltage and current required for your system).
Make sure sufficient air can flow around the radio and power
supply to allow adequate cooling.
SERVICE
This radio is designed for easy servicing. Refer to the
schematic diagrams, printed circuit board views, and alignment procedures contained in this manual.
NOTE
If you do not intend to use the 3.5-mm jack for the external speaker, fit the supplied speaker-jack cap to stop dust
and sand getting in.
4-3. Radio
The universal mount bracket allows the radio to be
mounted in a variety of ways. Be sure the mounting surface
is adequate to support the radio’s weight. Allow sufficient
space around the radio for air cooling. Position the radio
close enough to the vehicle operator to permit easy access
to the controls when driving.
4-4. DC Power and wiring
1. This radio may be installed in negative ground electrical
systems only. Reverse polarity will cause the cable fuse
to blow. Check the vehicle ground polarity before installa-
tion to prevent wasted time and effort.
2. Connect the positive power lead directly to the vehicle
battery positive terminal. Connecting the Positive lead to
any other positive voltage source in the vehicle is not rec-
ommended.
3. Connect the ground lead directly to the battery negative
terminal.
4. The cable provided with the radio is sufficient to handle
the maximum radio current demand. If the cable must be
extended, be sure the additional wire is sufficient for the
current to be carried and length of the added lead.
Antenna connector
speaker jack cap
Power input
connector
3
TK-7108
OPERATING FEATURES
1. Controls and Functions
1-1. Front Panel
q
we tr
u
1-2. Microphone
o
y
1-4. Display
i
Indicator Description
Lights while transmitting.
Lights when a signal is detected on
the currently selected channel.
Lights while the function pro-
grammed onto its corresponding key
is activated.
Lights while the function pro-
grammed onto its corresponding key
is activated.
Lights to display the currently se-
lected channel (1 ~ 4 or 5 ~ 8).
(Power) switch
q
Press to switch the transceiver ON. Press and hold for
approximately 1 second to switch the transceiver OFF.
w ▲ key
Press to increase the volume level.
e ▼ key
Press to decrease the volume level.
r ● key
PF (Programmable Function) key. The default setting of
this key is None (no function). The programmable
functions available for this key are listed below.
key
t
PF (Programmable Function) key. The default setting of
this key is Monitor (page 10). Other programmable
functions available for this key are listed below.
y 1 / 2 / 3 / 4 keys
Press to select a channel from 1 to 4. When using the
Group function, press to select a channel from 5 to 8.
u Microphone jack
Insert the microphone plug into this jack (the microphone
is an optional accessory).
i Speaker
Internal speaker.
o PTT switch
Press this switch, then speak into the microphone to call
a station.
1-5. Rear panel
Antenna connector
External
speaker jack
Power input
connector
1-3. Auxiliary Programmable Functions:
• Emergency • None (no function)
• Group • Scan On/ Off
• Key Lock • Talk Around
• Monitor • Temporary Delete
4
OPERATING FEATURES
TK-7108
2. Operation Features
The TK-7108 is a VHF FM radio designed to operate in
conventional format. The programmable features are summarized.
3. Transceiver Controls and Indicators
3-1. Front Panel Controls
All the keys on the front panel are momentary-type push
buttons. The functions of these keys are explained below.
• POWER key
Transceiver POWER key. When the power is switched
off, all the parameters are stored in memory. When the
power is switched on again, the transceiver returns to the
previous conditions.
• CHANNEL keys
• MONITOR key (Programmable)
• key (Programmable)
• VOLUME UP/DOWN key
When the key is pressed, the volume level is increased/
decreased and repeats if held for 200ms or longer.
• BUSY/TX LED
The BUSY indicator (Green LED) shows that the channel
is in use. The TX indicator (Red LED) shows that you are
transmitting.
3-2. Programmable Keys
The FPU (KPG-70D) enables programmable keys to select the following functions.
• Emergency • Talk Around
• Key Lock • Temporary Delete
•Monitor • None
• Scan ON/OFF • Group
• Emergency
Pressing this key for longer than 1 second causes the
transceiver to enter the emergency mode. The transceiver
jumps to the programmed "Emergency channel" and transmits for 25* seconds.
The transceiver disables mic mute while transmitting.
After finishing transmission, the transceiver receivers for 5*
seconds. The transceiver Mute* the speaker while receiving. Following the above sequence, the transceiver continues to transmit and receive.
* Default value.
• Key lock
Pressing this key causes the transceiver to accept entry
of only the [Vol Up/Down]*, [Key lock], Microphone [PTT],
[Monitor], [Emergency], and [Power] keys.
* Programmable
• Monitor
Used to release signalling (press once) or squelch (press
and hold for approximately two seconds) when operating as
a conventional. It is also used to reset option signalling.
• Talk around
Press this key, the transceiver uses the receive fre-
quency and the tone for transmission.
The operator can call the other party directly (without re-
peater). Press this key again, the talk around function goes off.
• Temporary delete
The "Add" channel contained in the scan sequence, and
"Delete" channel is not contained. In the scan mode, this
key switches the channel delete temporarily (Press and hold
for approximately one second).
When the transceiver is turned off, the transceiver exits
the scan or switches the scan function off.
• None
Sounds error operation beep, and no action will occur.
Use this function when the transceiver is required to be
more simple operated.
• Group
If Group has been programmed onto a key, press the
Group key to select the second group of channels. While
active, the LED beside the key lights. At this time, press a
key from 1 to 4 to select a channel from 5 to 8. To return to
channels 1 through 4, press the Group key again.
Note: You cannot use the Group function while operating
in Emergency mode.
4. Scan Operating
■ SCAN start condition
Two or more channels must be added to all channels that
can be scanned. The transceiver must be in normal receive
mode (PTT off).
When you activate the key programmed to the scan ON/
OFF function, the scan starts. The indicator next to the programmed key LED blinks.
■ Scan stop condition
The scan stops temporarily if the following conditions are
satisfied.
1) A carrier is detected, then QT/DQT matches on channels
for which receive the QT/DQT is set by the programming
software.
2) A carrier is detected on the channels for which receiving
QT/DQT is not set by the programming software or when
the monitor (signalling cancel) function is activated.
■ Revert channel
The revert channel is used to transmit during scanning
and set by the programming software (KPG-70D).
1) Selected channel
The transceiver reverts to the channel before scanning or
the channel that you changed during scan.
2) Selected with talkback
The transceiver reverts to the selected channel prior to
scan initiation.
However, if a call is received on a channel other then the
selected channel and PTT is pressed before scanning re-
sume, the transceiver "talks back" on the current receive
channel.
• Scan ON/OFF
Press this key starts scanning. Pressing this key stops
scanning.
■ Scan end
When you press the key programmed to the scan function during scan mode, the scan ends.
The indicator next to the programmed key LED turns off.
5
TK-7108
OPERATING FEA TURES
■ Temporary delete
It is possible to delete channel temporary during scan.
When scan stops on unnecessary channel for example by
interference of the other party, activate the delete function
(for example press and hold the key for approximately one
second), then that channel is deleted temporarily and scan
re-start immediately.
The temporary deleted channels return to pre-set delete/
add channels, when the transceiver is turned off or the scan
function is switched off.
5. Details of Features
■ Time-out timer
The time-out timer can be programmed in 30 seconds
increments from 30 seconds to five minutes and off. If the
transmitter is transmitted continuously for longer than the
programmed time, the transmitter is disabled and a warning
tone sounds while the PTT button is held down. The warning tone stops when the PTT button is released.
■ PTT ID
PTT ID provides a DTMF ANI to be sent with every time
PTT (beginning of transmission, end of transmission, or
both).
You can program PTT ID "on" or "off" for each channel.
The contents of ID are programmed each Radio.
The timing that the transceiver sends ID is programmable.
BOT : DTMF ID (Beginning of TX) is sent on beginning of
transmission.
EOT : DTMF ID (End of TX) is sent on end of transmis-
sion.
Both : DTMF ID (Beginning of TX) is sent on beginning of
transmission and DTMF ID (End of TX) is sent on end of
transmission.
■ Off hook decode
If the Off hook decode function has been enabled, removing and replacing the microphone on the hook has no
effect for decoding QT/DQT and option signalling.
■ "TOT" pre-alert
The transceiver has "TOT" pre-alert timer. This parameter
selects the time at which the transceiver generates "TOT"
pre-alert tone before "TOT" is expired.
"TOT" will be expired when the selected time passes
from a TOT pre-alert tone.
■ "TOT" re-key time
The transceiver has "TOT" re-key timer. This timer is the
time you can not transmit after "TOT" exceeded. After "TOT"
re-key time expired you can transmit again.
■ "TOT" reset time
The transceiver has "TOT" reset timer. This timer is the
minimum wait time allowed during a transmission that will
reset the "TOT" count.
"TOT" reset time causes the "TOT" to continue even after
PTT is released unless the "TOT" reset timer has expired.
6
■ Clear to transpond
The transceiver waits the transpond of DTMF if channel
is busy until channel open. This feature prevents the interference to other party.
6. Option Signalling (DTMF)
Built-in DTMF decoder is available for option signalling.
It is possible to use individual call, group call, Stun.
If the option signalling matches, a predetermined action
will occur.
If option signalling matches on a channel is set up with
option signalling, the channel LED will flash and option signalling will be released. The transpond or alert tone will
sound.
While option signalling matches (or if option signalling is
deactivated when you are transmitting), you can mute or
unmute QT/DQT/Carrier.
■ SP Unmute
You can select the type of SP Unmute system for each
channel. The selection is as follows.
Carrier, QT/DQT:
Channel with this option will not check ID Code in order
to open its speaker.
Carrier+DTMF, QT/DQT+DTMF:
Channel that is set with this option will have to check for
ID Code in order to open its speaker.
Default:
Carrier, QT/DQT.
SP Unmute
Carrier None
Carrier+DTMF
QT/DQT Yes
QT/DQT+DTMF
Note:
When QT/DQT is not used, QT/DQT and QT/DQT+DTMF
can not be selected.
When DTMF is not used, Carrier+DTMF and QT/
DQT+DTMF can not be selected.
Channel Setting
QT/DQT DTMF Condition
None Carrier Sounds
Yes
None Yes
None
Yes
Yes Yes
RX Condition
Carrier Sounds
Carrier+DTMF Sounds
Carrier Not Sounds
Carrier+DTMF Sounds
Carrier Not Sounds
Carrier+QT/DQT
Carrier Not Sounds
Carrier+QT/DQT
Carrier+QT/DQT+DTMF
Carrier+DTMF Not Sounds
Carrier Not Sounds
Carrier+QT/DQT
Carrier+QT/DQT+DTMF
Carrier+DTMF Not Sounds
■ Auto Reset
If option signalling matches a group set up with option
signalling, option signalling is released. After matching option signalling, option signalling will temporarily reset automatically.
Speaker
Sounds
Sounds
Sounds
Not Sounds
Sounds
OPERATING FEA TURES / REALIGNMENT
User mode
PC mode
Data programming mode
PC test mode
PC tuning mode
Clone mode
TK-7108
■ Stun
If the stun code matches, a predetermined action will occur. Whether option signalling is activated or not, when
stun matches on any channel, the transceiver will become
TX inhibited or TX/RX inhibited. While stun is active, if the
stun code + "#" code is received, stun will deactivate.
When stun matches, transpond will function. Alert will
not be output.
7. Audible User Feedback Tones
The transceiver outputs various combinations of tones to
notify the user of the transceiver operating state.
Refer to the help file on the KPG-70D, regarding the functions that are not listed below.
■ Stun on tone
When a stun code is received, transpond tone sounds.
■ Stun off tone
When a stun release code is received, transpond tone
sounds.
■ Group call tone
Sounds when a group call with the correct DTMF option
signalling is received, repeats 7 times. You can select yes or
no in the Alert tone level setting.
■ Individual call tone
Sounds when an individual call with the correct DTMF
option signalling is received. You can select yes or no in the
Alert tone level setting.
REALIGNMENT
1. Modes
Mode Function
User mode For normal use.
PC mode Used for communication between the
radio and PC (IBM compatible).
Data programming Used to read and write frequency data
mode and other features to and from the radio.
PC test mode Used to check the radio using the PC.
This feature is included in the FPU.
PC tuning mode Used to tune the radio using the PC.
Clone mode Used to transfer programming data from
one radio to another.
2. How to Enter Each Mode
Mode Operation
User mode Power ON
PC mode Received commands from PC
Clone mode [1]+Power ON (Two seconds)
■ Key input error tone
Sounds when a key is pressed but that key cannot be
used. You can select yes or no for the optional feature's
warning tone.
■ Transpond tone
Sounds when an individual call with the correct DTMF
option signalling is received. For group calls, only the group
tone will sound, not the transpond tone.
■ Pre alert tone
Sounds prior to the TOT TX inhibit activation. If TOT pre
alert is set, the tone sounds at the amount of time programmed, before the TOT expires (TOT time – TOT pre alert
time = Pre alert tone sounding time). You can select yes or
no for the optional feature's warning tone.
■ Transmit protection
The power module is protected against heat while transmitting by making the radio cuts down TX power when the
temperature of the power module becomes higher than reference. After that, if the temperature continue to rise, transmission is stopped. The power module is also protected
against over voltage by having the radio to check that the
voltage of power supply connected to the radio is not higher
than about 17V when the radio is turned on, otherwise it can
not transmit. In both cases when transmission is stopped, a
beep will continue to sound until the PTT key is released.
3. PC Mode
3-1. Preface
The TK-7108 transceiver is programmed using a personal
computer, a programming interface (KPG-46) and programming software (KPG-70D).
The programming software can be used with an IBM PC
or compatible. Figure 1 shows the setup of an IBM PC for
programming.
3-2. Connection Procedure
1. Connect the TK-7108 to the personal computer with the
interface cable.
2. When the Power is switched on, user mode can be en-
tered immediately. When the PC sends a command, the
radio enters PC mode.
When data is transmitted from transceiver, the red LED
blink.
When data is received by the transceiver, the green LED
blink.
In the PC mode, 4CH LEDs, [MON] LED and [
turned on.
Notes :
• The data stored in the personal computer must match
model type when it is written into the EEPROM.
• Attach the interface cable, then change the TK-7108 to
PC mode.
] LED are
7
TK -7108
REALIGNMENT
3-3. KPG-46 Description
(PC programming interface cable : Option)
The KPG-46 is required to interface the TK-7108 to the
computer. It has a circuit in its D-subconnector (25-pin) case
that converts the RS-232C logic level to the TTL level.
The KPG-46 connects the modular microphone jack of
the TK-7108 to the computers RS-232C serial port.
KPG-46
IBM-PC
KPG-70D
TK-7108
Fig. 1
3-4. Programming Software Description
The KPG-70D programming disk is supplied in 3-1/2" disk
format. The software on this disk allows a user to program
TK-7108 radio via a programming interface cable (KPG-46).
Adding the data password.
If the data password is set in the optional feature menu,
you must enter the password (Master transceiver) to activate a clone mode.
you can use 1, 2, 3, and 4 to configure the password. The
maximum length of the password is 10 digits.
1. [1]+Power ON.
2. [1]~[4] LED, and MON LED are turned ON.
3. Enter the password using [1]~[4] keys.
4. Press [MON] key.
5. If the password matches, the transceiver enters a clone
mode. Otherwise, transceiver beeps and returns to the
password input mode.
Cloning cable
(E30-3382-05)
3-5. Programming With IBM PC
If data is transferred to the transceiver from an IBM PC
with the KPG-70D, the destination data (basic radio information) for each set can be modified.
4.Clone Mode
Programming data can be transferred from one radio to
another by connecting them via their modular microphone
jacks. The operation is as follows (the transmit radio is the
master and the receive radio is the slave).
NOTE: Clone mode should enabled.
1. Turn the master TK-7108 power ON with the [1] key held
down. The TK-7108 [
2. Power on the slave TK-7108.
3. Connect the cloning cable (No. E30-3382-05) to the
modular microphone jacks on the master and slave.
4. Press the [ ] key on the master TK-7108 transceiver. The
data of the master is sent to the slave. While the master
is sending data, [TX] LED blinked. While the slave is re-
ceiving the data, 4 LEDs, [MON] LED, [
on and [BUSY] LED blinked. When cloning of data is com-
pleted, the master [TX] LED turned off, and the slave au-
tomatically operates in the User mode. The slave can
then be operated by the same program as the master.
5. The other slave can be continuously cloned. Carry out
the operation in step 2 to 4.
] LED is turned on.
] LED are turned
Fig. 2
8
DISASSEMBLY FOR REP AIR
TK -7108
1. When you remove the panel, turn the transceiver up
side down. Detach the panel by lifting the tabs as
shown below.
tabs
Fig. 1
3. To remove the display unit PCB, detach the PCB by
lifting at the indents of the PCB as shown below.
indents
Fig. 3
2. To remove the cabinet, first turn the transceiver up
side down. Detach the cabinet by prying the tabs as
shown below.
tabs
tabs
Fig. 2
4. When mounting the front panel, match the 4 tabs of
the chassis with the panel, being sure they attach
securely.
tabs
tabs
Fig. 4
9
TK-7108
CIRCUIT DESCRIPTION
Frequency Configuration
The receiver utilizes double conversion. The first IF is
49.95MHz and the second IF is 450kHz. The first local oscillator signal is supplied from the PLL circuit.
The PLL circuit in the transmitter generates the neces-
sary frequencies. Figure 1 shows the frequencies.
ANT
ANTSWRF
POWER
AMP
AMP
RF
AMP
1st
MIX
MCF
49.95MHz
RX
TX
1/2
CF 450kHz
IF SYSTEM
50.4MHz
X3
multiply
TCXO
PLL/VCO
AF
PA
16.8MHz
MIC
AMP
SP
MIC
Fig. 1 Frequency configuration
Receiver System
The receiver is double conversion superheterodyne. The
frequency configuration is shown in Figure 1.
■ Front-end RF Amplifier
An incoming signal from the antenna is applied to an RF
amplifier (Q26) after passing through a transmit/receive
switch circuit (D31 is off) and a band pass filter (L36, L38
and varactor diodes: D25, D26). After the signal is amplified
(Q26), the signal is filtered through a band pass filter (L30,
L32 and varactor diodes: D21, D22) to eliminate unwanted
signals before it is passed to the first mixer.
The voltage of these diodes are controlled by tracking the
CPU (IC6) center frequency of the band pass filter. (See Fig. 2)
■ First Mixer
The signal from the RF amplifier is heterodyned with the
first local oscillator signal from the PLL frequency synthesizer circuit at the first mixer (Q21) to create a 49.95MHz
first intermediate frequency (1st IF) signal. The first IF signal
is then fed through two monolithic crystal filters (MCFs :
XF1) to further remove spurious signals.
■ IF Amplifier
The first IF signal is amplified by Q19, and the enters IC5
(FM processing IC). The signal is heterodyned again with a
second local oscillator signal within IC5 to create a 450kHz
second IF signal. The second IF signal is then fed through a
450kHz ceramic filter (Wide : CF1, Narrow : CF2) to further
eliminate unwanted signals before it is amplified and FM detected in IC5.
Item Rating
Nominal center frequency 49.95MHz
Pass bandwidth ±5.0kHz or more at 3dB
35dB stop bandwidth ±20.0kHz or less
Ripple 1.0dB or less
Insertion loss 5.0dB or less
Guaranteed attenuation
Terminal impedance 350 / 5.5pF
80dB or more at fo±1MHz
Spurious : 40dB or more within fo±1MHz
Table 1 Crystal filter (L71-0591-05) : XF1
Item Rating
Nominal center frequency 450kHz
6dB bandwidth ±6.0kHz or more
50dB bandwidth ±12.5kHz or less
Ripple 2.0dB or less
Insertion loss 6.0dB or less
Guaranteed attenuation 35.0dB or more within fo±100kHz
Terminal impedance 2.0k
Table 2 Ceramic filter (L72-0993-05) : CF1
Item Rating
Nominal center frequency 450kHz
6dB bandwidth ±4.5kHz or more
50dB bandwidth ±10.0kHz or less
Ripple 2.0dB or less
Insertion loss 6.0dB or less
Guaranteed attenuation 60.0dB or more within fo±100kHz
Terminal impedance 2.0k
Table 3 Ceramic filter (L72-0999-05) : CF2
CF1 (Wide)
10
ANT
D30,31
ANT
SW
IC3
D/A
L36,38
D25,26
BPF
TV
CPU
Q26
RF AMP
L30,32
D21,22
BPF
1/2 divider
1st local
OSC (VCO/PLL)
Q21
MIX
IC23
XF1
MCF
Q19
IF AMP
X1
TCXO
Fig. 2 Receiver system
CF2 (Narrow)
IC5
IF system
Q6
X3 multiply
IC3
D/A CONVERTER
DEO
CIRCUIT DESCRIPTION
Q18
NOISE AMP
D18IC5 IC6
AF
RSSI
DET
CPU
IF
SYSTEM
SQIN
RSSI
TK-7108
■ Wide/Narrow Changeover Circuit
The Wide port (pin 92) and Narrow port (pin 91) of the
CPU is used to switch between ceramic filters. When the
Wide port is high, the ceramic filter SW diodes (D13, D15)
cause CF1 to turn on to receive a Wide signal.
When the Narrow port is high, the ceramic filter SW diodes
(D13, D15) cause CF2 to turn on to receive a Narrow signal.
IC5
R78
IF System
R73
R77
Wide
IC6 92pin
Narrow
IC6 91pin
IF_IN MIX_O
CF1
(Wide)
CF2
D13 D15
(Narrow)
R74
Fig. 3 Wide/Narrow changeover circuit
■ AF Signal System
The detection signal from IF IC (IC5) goes to D/A converter (IC3) to adjust the gain and is output to AF filter (IC10)
for characterizing the signal. The AF signal output from IC10
and the DTMF signal, BEEP signal are summed and the resulting signal goes to the D/A converter (IC3). The AFO output level is adjusted by the D/A converter. The signal output
from the D/A converter is input to the audio power amplifier
(IC102). The AF signal from IC102 switches between the
internal speaker and speaker jack (J1) output.
IC5
IF IC
IC3 IC10
DEO
D/A
CONV.
AF
Filter
IC3
D/A
CONV.
IC102 SP
AF PA
■ Squelch Circuit
The detection output from the FM IF IC (IC5) passes
through a noise amplifier (Q18) to detect noise. A voltage is
applied to the CPU (IC6). The CPU controls squelch according to the voltage (SQIN) level. The signal from the RSSI pin
of IC5 is monitored. The electric field strength of the receive signal can be known before the SQIN voltage is input
to the CPU, and the scan stop speed is improved.
Fig. 5 Squelch circuit
PLL Frequency Synthesizer
The PLL circuit generates the first local oscillator signal
for reception and the RF signal for transmission.
■ PLL
The frequency step of the PLL circuit is 5 or 6.25kHz. A
16.8MHz reference oscillator signal is divided at IC1 by a
fixed counter to produce the 5 or 6.25kHz reference frequency. The voltage controlled oscillator (VCO) output signal is buffer amplified by Q15, then divided in IC1 by a dualmodule programmable counter. The divided signal is compared in phase with the 5 or 6.25kHz reference signal in the
phase comparator in IC1. The output signal from the phase
comparator is filtered through a low-pass filter and passed
to the VCO to control the oscillator frequency. (See Fig. 6)
■ VCO
The operating frequency is generated by Q11 in transmit
mode and Q10 in receive mode. The oscillator frequency is
controlled by applying the VCO control voltage, obtained
from the phase comparator, to the varactor diodes (D10 and
D12 in transmit mode and D9 and D11 in receive mode).
The TX/RX pin is set low in receive mode causing Q12 and
Q7 to turn Q11 off, and turn Q10 on. The TX/RX pin is set
high in transmit mode. The outputs from Q10 and Q11 are
amplified by Q15 and sent to the RF amplifiers.
FIg. 4 AF signal system
11
TK-7108
CIRCUIT DESCRIPTION
IC1 : PLL IC
5kHz/6.25kHz
1/N
PLL
DATA
16.8MHz
REF
OSC
1/M
Phase
comparator
5kHz/6.25kHz
Charge
pump
Fig. 6 PLL circuit
■ Unlock Circuit
During reception, the 8RC signal goes high, the 8TC signal goes low, and Q29 turns on. Q31 turns on and a voltage
is applied to the collector (8R). During transmission, the
8RC signal goes low, the 8TC signal goes high and Q30
turns on. Q33 turns on and a voltage is applied to 8T.
The CPU in the control unit monitors the PLL (IC1) LD
signal directly. When the PLL is unlocked during transmission, the PLL LD signal goes low. The CPU detects this
signal and makes the 8TC signal low. When the 8TC signal
goes low, no voltage is applied to 8T, and no signal is transmitted.
8R 8T
Q31
SW
8C
Q33
SW
LPF
D10,12
D9,11
Q11
TX VCO
Q10
RX VCO
Q15
BUFF
AMP
Q7,12
T/R SW
Q3
AMP
Transmitter System
■ Outline
The transmitter circuit produces and amplifies the desired frequency directly. It FM-modulates the carrier signal
by means of a varicap diode.
■ Power Amplifier Circuit
The transmit output signal from the VCO passes through
the transmission/reception selection diode (D19) and amplified to a specified level of the power module (IC101) by the
drive block (Q23 and Q25). The amplified signal goes to a
low-pass filter. The low-pass filter removes unwanted highfrequency harmonic components, and the resulting signal is
goes the antenna terminal.
Q29
SW
Q30
SW
8RC
LD
IC6
CPU
Fig. 7 Unlock circuit
IC22IC21(1/2)MIC
MIC/IDC
NJM2100V
MIC KEY
INPUT
IC3 Q11
D/A
CONVERTER
M62363FP
X1
TCXO
16.8MHz
Splatter
FILTER
NJM2904V
CPU
784214GC
VCO
2SK508NV
(K52)
IC1
PLL
MB15A02
8TC
IC6
IC1
PLL
PLL lock
: LD "H"
Q15
BUFFER
2SC5108
(Y)
Q3
RF AMP
2SC4649
(N,P)
IC4
SUM AMP
NJM2902V
IC3
D/A
CONVERTER
M62363FP
IC3
D/A
CONVERTER
M62363FP
IC23
1/2
DIVIDER
UPB1509GV
BUFFER
NJM2902V
Q20
RF AMP
2SC4649
(N,P)
IC4
Q23
RF AMP
2SC3357
Q25
RF AMP
2SC2954
IC101
POWER AMP
M67741H-32
ANT
12
Fig. 8 Transmitter system
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