Circuit Description - Kenwood TK-3202 Service Manual

TK-3202/3206
1. Frequency Configuration
The receiver utilizes double conversion. The first IF is 38.85
MHz and the second IF is 450 kHz. The first local oscillator
signal is supplied from the PLL circuit.
The PLL circuit in the transmitter generates the necessary
frequencies. Fig. 1 shows the frequencies.
ANT TX/RX: 450 ~ 490MHz (TK-3202(K,M), TK-3206(M))
400 ~ 430MHz (TK-3206(M3))
470 ~ 512MHz (TK-3202(K2,M2))
RF
ANT SW
AMP
TX: 450 ~ 490MHz
(TK-3202(K,M), TK-3206(M))
400 ~ 430MHz
(TK-3206(M3))
470 ~ 512MHz
(TK-3202(K2,M2))
TX
AMP
Fig. 1 Frequency configuration
2. Receiver
The frequency configuration of the receiver is shown in Fig. 2.
ANT
RF AMP
BPF
ANT SW
TUNE
CF201
IC201
IF,MIX,DET
X1
Q1
TCXO
X3 multiply
2nd Local
Fig. 2 Receiver section
1) Front End (RF AMP)
The signal coming from the antenna passes through the
transmit/receive switching diode circuit, (D103,D104,D106
and D122) passes through a BPF (L229 and L228), and is
amplified by the RF amplifier (Q205).
The resulting signal passes through a BPF (L214,L212 and
L211) and goes to the mixer. These BPFs are adjusted by
variable capacitors (D203,D204,D205,D206 and D210). The
input voltage to the variable capacitor is regulated by
voltage output from the microprocessor (IC405).
2) First Mixer
The signal from the front end is mixed with the first local
oscillator signal generated in the PLL circuit by Q1 to
produce a first IF frequency of 38.85 MHz.
The resulting signal passes through the XF201 MCF to cut
the adjacent spurious and provide the opitimun
characteristics, such as adjacent frequency selectivity.
8

CIRCUIT DESCRIPTION

CF
450kHz
MCF
IF SYSTEM
AMP
38.85MHz
38.4MHz
RX: 411.15 ~ 451.15MHz
(TK-3202(K,M), TK-3206(M))
X3 multiply
361.15 ~ 391.15MHz
TCXO
(TK-3206(M3))
431.15 ~ 473.15MHz
(TK-3202(K2,M2))
RF PLL
MIC
AMP VCO
AMP
MIXER MCF
Q205 BPF Q204 XF201
TUNE 1st Local
IC301
IC302
AF PA
AF VOL
AQUA
12.8MHz
3) IF Amplifier Circuit
The first IF signal is passed through a four-pole monolithic
crystal filter (XF201) to remove the adjacent channel signal.
The filtered first IF signal is amplified by the first IF amplifier
(Q203) and then applied to the lF system IC (IC201). The IF
system IC provides a second mixer, second local oscillator,
limiting amplifier, quadrature detector and RSSI (Received
Signal Strength Indicator). The second mixer mixes the first
IF signal with the 38.4MHz of the second local oscillator
SP
output (TCXO X1) and produces the second IF signal of
AF
450kHz.
The second IF signal is passed through the ceramic filter
(CF201) to remove the adjacent channel signal. The filtered
12.8MHz
second IF signal is amplified by the limiting amplifier and
demodulated by the quadrature detector with the ceramic
MIC
discriminator (CD201). The demodulated signal is routed to
the audio circuit.
4) Wide/Narrow Switching Circuit
Narrow and Wide settings can be made for each channel
by switching the demodulation level.
The WIDE (low level) and NARROW (high level) data is
output from IC405, pin 45.
When a WIDE (low level) data is received, Q202 turn on.
IF AMP
When a NARROW (high level) data is received, Q202 turn
Q203
off.
Q202 turns off/on with the Wide/Narrow data and the IC201
detector output level is switched to maintain a constant
output level during wide or narrow signals.
SP
RX_W/N
(IC405)
L : Wide
H : Narrow
Fig. 3 Wide/Narrow switching circuit
5) Audio Amplifier Circuit
The demodulated signal from IC201 goes to AF amplifier
through IC301.
The signal then goes through an AF volume control, and is
routed to an audio power amplifier (IC302) where it is amplified
and output to the speaker.
AFOUT
QUAD IFOUT
C214
R211
Q202
CD201
R213
Q203
IC201
FM IF SYSTEM
5R