Circuit Description - Kenwood TK-3202 Service Manual

■ 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 38.85MHz.
The resulting signal passes through the XF201 MCF to cut
the adjacent spurious and provide the optimum characteris-
tics, such as adjacent frequency selectivity.
■ 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 out-
put (TCXO X1) and produces the second IF signal of 450kHz.
The second IF signal is passed through the ceramic filter
(CF201) to remove the adjacent channel signal. The filtered
second IF signal is amplified by the limiting amplifier and de-
modulated by the quadrature detector with the ceramic dis-
criminator (CD201). The demodulated signal is routed to the
audio circuit.
■ Wide 5k/Wide 4k, Narrow Switching Circuit
Narrow and Wide 5k, Wide 4k 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.
When a NARROW (high level) data is received, Q202 turn off.
Q202 turns off/on with the Wide/Narrow data and the
IC201 detector output level is switched to maintain a con-
stant output level during wide or narrow signals.
Q202
RX_W/N
(IC405)
L : Wide 5k/4k
H: Narrow
Fig. 3 Wide 5k/Wide 4k, Narrow switching circuit

CIRCUIT DESCRIPTION

Q203
AFOUT
IC201
FM IF SYSTEM
QUAD IFOUT
R211
5R
■ 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 ampli-
fied and output to the speaker.
■ Squelch
Part of the AF signal from the IC enters the FM IC (IC201)
again, and the noise component is amplified and rectified by a
filter and an amplifier to produce a DC voltage corresponding
to the noise level.
The DC signal from the FM IC goes to the analog port of
the microprocessor (IC405). IC405 determines whether to
output sounds from the speaker by checking whether the in-
put voltage is higher or lower than the preset value.
To output sounds from the speaker, IC405 sends a high
signal to the SP MUTE line and turns IC302 on through Q303,
Q304, Q305, Q306 and Q316. (See Fig. 4.)
IC201: FM IF
IF amp
SIGNAL
DTMF
QT/DQT
BUSY QT/DQT IN
IC405
CLK, DATA,
STD, LOADN
CPU
AF CONT
Fig. 4 AF amplifier and Squelch
■ Receive Signaling
• QT/DQT
The output signal from FM IC (IC201) enters the micropro-
cessor (IC405) through IC301. IC405 determines whether
the QT or DQT matches the preset value, and controls the SP
MUTE and the speaker output sounds according to the
squelch results.
TK-3202
IC301
AQUA-L
IC302 Q306,316
AF PA SW SP
Q303,304,305
SW
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