Circuit Description - Kenwood TK-3301 Service Manual

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.
TX/RX : 446.00625~
446.09375MHz
ANT
1st MIX
MCF
ANT RF
SW AMP
38.85MHz
RX:
407.15625~
407.24375
MHz
TX
AMP
TX: 446.00625~
446.09375MHz
Fig. 1 Frequency confi guration
2. Receiver
The receiver is double conversion super-heterodyne, de-
signed to operate in the frequency range 446MHz.
The frequency confi guration of the receiver is shown in
Fig. 2.
ANT RF AMP
BPF Q204
ANT
SW
CF201
IC201 IC308
IF, MIX, DET AQUA-L
Q2 X1
X3 multiply TCXO
2nd Local 12.8MHz
Fig. 2 Receiver section
■ Front End (RF AMP)
The signal coming from the antenna passes through the
transmit/receive switching diode circuit, (D103, D104 and
D106) passes through a BPF (L213 and L212), and is ampli-
fi ed by the RF amplifi er (Q204).
The resulting signal passes through a BPF (L209, L207
and L206) and goes to the mixer. These BPFs are non-vari-
able type.

CIRCUIT DESCRIPTION

CF
450kHz
SP
IF AF
SYSTEM AMP
38.4MHz
X3
TCXO 12.8MHz
multiply
MIC
RF PLL MIC
AMP AMP
VCO
MIXER MCF IF AMP
BPF Q203 XF201 Q202
1st Local
IC309
SP
AF VOL AF PA
■ First Mixer
The signal from the front end is mixed with the fi rst local
oscillator signal generated in the PLL circuit by Q203 to pro-
duce a fi rst IF frequency of 38.85MHz.
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 monolithic
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-
fier (Q202) and then applied to the lF system IC (IC201).
The IF system IC provides a second mixer, limiting amplifi er,
quadrature detector and RSSI (Received Signal Strength In-
dicator). The second mixer mixes the fi rst IF signal with the
38.4MHz of the second local oscillator output (TCXO X1 and
Q2) and produces the second IF signal of 450kHz.
The second IF signal is passed through the ceramic fi lter
(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 IC308.
The signal then goes through an AF volume control , and
is routed to an audio power amplifi er (IC309) 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
of the MCU (IC306). IC306 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, IC306 sends a high
signal to the AF_CONT line and turns IC309 on through
Q312, Q313, Q314, Q315 and Q316. (See Fig. 4)
IC201: FM IF
IF amp
SIGNAL
DTMF
QT/DQT
BUSY QT/DQT IN
IC306
CLK, DATA,
STD, LOADN
MCU
AF_CONT
Fig. 3 AF amplifi er and squelch
TK-3301
IC308
AQUA-L
IC309
AF PA
Q315,316 SP
SW
SW
Q312,313,314
7