Circuit Description - Kenwood TK-2302 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 : 136~174MHz
ANT
1st MIX
MCF
ANT RF
SW AMP
38.85MHz
RX:
174.85~
212.85MHz
RF
TX
AMP
AMP
TX: 136~174MHz
Fig. 1 Frequency confi guration
2. Receiver
The frequency confi guration of the receiver is shown in
Fig. 2.
ANT RF AMP
BPF Q204
ANT
SW
RCTV
CF201
IC201 IC308
IF, MIX, DET AQUA-L
Q2 X1
X3 multiply TXCO
2nd Local 12.8MHz
Fig. 2 Receiver sectio
■ Front End (RF AMP)
The signal coming from the antenna passes through the
transmit/receive switching diode circuit, (D103, D104 and
D105) passes through a BPF (L214, L216 and L213), and is
amplifi ed by the RF amplifi er (Q204).
The resulting signal passes through a BPF (L209 and
L211) and goes to the mixer. These BPFs are adjusted by
variable capacitors (D203, D204, D205 and D202). The input
voltage to the variable capacitor is regulated by voltage out-
put from the MCU (IC306).

CIRCUIT DESCRIPTION

CF
450kHz
SP
IF
AF
SYSTEM
AMP
38.4MHz
X3
TCXO 12.8MHz
multiply
MIC
PLL
MIC
1/2
AMP
VCO
MIXER MCF IF AMP
BPF Q203 XF201 Q202
PCTV 1st Local
IC309
AF VOL SP
AF PA
TK-2302/2302
■ 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.
■ 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 IC306, pin 5. When a WIDE (low level) data is
received, Q201 turn on. When a NARROW (high level) data
is received, Q201 turn off.
Q201 turns on/off 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.
AFOUT
Q201
W/N
(IC306)
L : Wide
H: Narrow
Fig. 3 Wide/Narrow switching 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.
V /2306
( )
Q202
IC201
FM IF SYSTEM
QUAD IFOUT
R209
5R
9