Circuit Description; Frequency Configuration; Wide/ Narrow/ Apco Switching Circuit; Front-End Rf Amplifier - Kenwood TK-5210 Service Manual

1. Overview
This transceiver is a VHF/FM/APCO portable transceiver
designed to operate in the frequency range of 136 to
174MHz.
The unit consists of receiver, transmitter, phase-locked
loop (PLL) frequency synthesizer, base band parts, power
supply, and control circuits.

2. Frequency Configuration

The receiver is a double-conversion superheterodyne
using first intermediate frequency (IF) of 49.95MHz and
second IF of 450kHz. Incoming signals from the antenna are
mixed with the local signal from the PLL circuit to produce
the first IF of 49.95MHz.
This is then mixed with the 50.4MHz second local
oscillator output to produce the 450kHz second IF. This
signal is detected to give the demodulated signal in the DSP.
The transmit signal frequency is generated by the PLL
VCO, and modulated by the signal from the DSP. It is then
amplified and fed to the antenna.
ANT
TX/RX : 136~174MHz
1st MIX
MCF
RF
ANT
SW AMP
49.95MHz
16.8MHz x3
VCXO
50.4MHz
185.95~
223.95MHz
PA
TX
AMP
AMP
136~174MHz
Fig. 1 Frequency configuration
3. Receiver System

3-1. Front-end RF Amplifier

The signal is passed through an antenna matching coil,
where the high-frequency components are amplified by a
GaAs FET(Q202). The signals are then fed into band-pass
filter that uses varactor diode tuning to reject unwanted
signal components, and is fed to the 1st mixer.
3-2. 1st Mixer
The 1st mixer uses the GaAs IC (IC202). The 1st mixer
mixes the signal with the 1st local oscillator frequency from
the VCO, and converts it to the 1st IF (49.95MHz).
The signal then passes through monolithic crystal filter
(XF201) to remove unnecessary nearby frequency
components. The signal from the MCF is used as the 1st IF
signal.
3-3. IF Amplifier
The 1st IF signal is amplified by the IF amplifier (Q204) and
fed into the FM IC (IC204). The IF signal is then mixed with
the 2nd local oscillator frequency of 50.4MHz to generate the

CIRCUIT DESCRIPTION

CF
450kHz
SP
MIX AF
IF AMP AMP
FPGA
A/D
D/A
DSP
MIC
MIC
PLL
VCO AMP
2nd IF of 450KHz. The 450KHz signal is then passed through
a ceramic filter (CF201) and fed back into IC204 for additional
amplification.
L201 Q202 L202
BPF LNA BPF
TUNE
XF201
MCF IF AMP
49.95MHz
Fig. 2 Receiver section

3-4. Wide/ Narrow/ APCO Switching Circuit

Narrow and Wide and APCO settings can be made for
each channel by switching the ceramic filters CF203 (Wide),
CF204 (Narrow), CF202 (APCO).
The Wide and Narrow and APCO data is output from pin54
(WN) and pin55 (VN) of CPU (IC5).
When a Wide data (VN : low level, WN : high level) is
received, the 450KHz signal is passed through a ceramic filter
(CF203). When a Narrow data (VN : low level, WN : low level)
is received, the 450KHz signal is passed through a ceramic
filter (CF204). When a APCO data (VN : high level, WN : high
level) is received, the 450KHz signal is passed through a
ceramic filter (CF202).
If the 450kHz signal is a FM signal(Wide, Narrow), the
signal is detected by a ceramic discriminator (CD201). AF
signal is fed to CODEC(IC406), the AF level is adjusted and it
is output from 15pin of IC406. Q209 turns on/off with the
Wide/Narrow data and the IC204 detector output level is
changed to maintain a constant output level during Wide or
Narrow signals.
If the 450kHz signal is an APCO signal, the signal is
prepared by the buffer amplifier (IC208) and fed to FPGA
(IC13). The APCO signal is A/D-converted by the FPGA and
DSP (IC8), and is performed APCO demodulation.
The AF signal is output from 15pin of CODEC (IC406).
VN WN Filter
H H APCO
L H Wide
IC203
L L Narrow
CF201
VN
450kHz
49.95MHz
X201
Q205
VCXO
50.4MHz
x3 16.8MHz
Fig. 3 Wide/Narrow/APCO switching circuit
TK-5210
L204 L205 IC202
BPF BPF 1st MIXER
1st Local OSC
Q204
IC204
FM IC
2nd Local OSC
Tripler
Q205
X3
CF201
X201
VCXO
16.8MHz
CF202
APCO
IC205
CF204
Narrow
IC206 IC207
CD201
AF
CF203
VN
CD
Wide
WN WN
DET
IC204
FM IC
APCO
13