Circuit Description - Kenwood TK-361SA Service Manual

TK-361SA
1. Frequency Confi guration
The receiver utilizes double conversion. The first IF is
38.85MHz and the second IF is 450kHz. The fi rst local oscil-
lator signal is supplied from the PLL circuit.
The PLL circuit in the transmitter generates the neces-
sary frequencies. Fig. 1 shows the frequencies.
ANT 463.975~464.375MHz
1st MIX
ANT RF
SW AMP
38.85MHz
425.125~
425.525MHz
TX
AMP
463.975~464.375MHz
Fig. 1 Frequency confi guration
2. Receiver
The frequency confi guration of the receiver is shown in
Fig. 2.
ANT RF AMP
BPF Q205
ANT
SW
PCTV
CF201
IC201
IF, MIX, DET
Q1
X3 multiply
2nd Local
Fig. 2 Receiver section
■ 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 amplifi ed by the RF amplifi er (Q205).
The resulting signal passes through a BPF (L214, L212
and L211) and goes to the mixer (Q204). These BPFs are
adjusted by variable capacitors (D203, D204, D205, D206
and D210). The input voltage to the variable capacitor is reg-
ulated by voltage output from the micro control unit (MCU)
(IC405).
■ First Mixer
The signal from the front end is mixed with the fi rst local
oscillator signal generated in the PLL circuit by Q3 to pro-
duce a fi rst IF frequency of 38.85MHz.
8

CIRCUIT DESCRIPTION

CF
450kHz
MCF
IF AF
SYSTEM AMP
38.4MHz
X3
TCXO 12.8MHz
multiply
RF PLL MIC
AMP
AMP VCO
MIXER MCF IF AMP
BPF Q204 XF201 Q203
PCTV 1st Local
IC302
AF VOL
AF PA
IC301
AQUA-L
X1
TCXO
12.8MHz
The resulting signal passes through the XF201 MCF to
cut the adjacent spurious and provide the opitimun charac-
teristics, such as adjacent frequency selectivity.
■ IF Amplifi er Circuit
The fi rst IF signal is passed through a four-pole mono-
lithic crystal fi lter (XF201) to remove the adjacent channel
signal.
The fi ltered fi rst IF signal is amplifi ed by the fi rst IF ampli-
fi er (Q203) and then applied to the lF system IC (IC201). The
IF system IC provides a second mixer, second local oscilla-
SP
tor, limiting amplifi er, quadrature detector and RSSI (Received
Signal Strength Indicator). The second mixer mixes the fi rst
IF signal with the 38.4MHz of the second local oscillator
output (Q1) and produces the second IF signal of 450kHz.
The second IF signal is passed through the ceramic fi lter
MIC
(CF201) to remove the adjacent channel signal. The fi ltered
second IF signal is amplified by the limiting amplifier and
demodulated by the quadrature detector with the ceramic
discriminator (CD201). The demodulated signal is routed to
the audio circuit.
■ Audio Amplifi er Circuit
The demodulated signal from IC201 goes to AF amplifi er
through IC301.
The signal then goes through an AF volume control, and
is routed to an audio power amplifi er (IC302) where it is am-
plifi ed 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 amplifi ed and rectifi ed by
a fi lter and an amplifi er to produce a DC voltage correspond-
ing to the noise level.
The DC signal from the FM IC goes to the analog port
SP
of the MCU (IC405). IC405 determines whether to output
sounds from the speaker by checking whether the input
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. 3)
IC201 FM IF
IF AMP
BUSY QT/DQT IN
IC405
MCU
AF CONT
Fig. 3 AF amplifi er and squelch
SIGNAL
IC301
AQUA-L
QT/DQT
IC302 Q306,316
AF PA SW
CLK, DATA,
STD, LOADN
Q303,304,305
SW
SP