Circuit Description - Kenwood TK-3160 Service Manual

TK-3160
1. Frequency Configuration
The receiver utilizes double conversion. The first IF is 49.95
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.
TX/RX: 440 ~ 470MHz (E)
ANT
470 ~ 512MHz (X2)
RF
ANT SW
AMP
TX: 440 ~ 470MHz (E)
470 ~ 512MHz (X2)
TX
AMP
Fig. 1 Frequency configuration
2. Receiver
The frequency configuration of the receiver is shown in Fig. 2.
ANT
BPF
ANT SW
TUNE
CF401
IC602
AF Amp
IC401
IF,MIX,DET
X1
Q4
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, (D204,D206,D208
and D212) passes through a BPF (L413 and L414), and is
amplified by the RF amplifier (Q404).
The resulting signal passes through a BPF (L409,L408 and
407) and goes to the mixer. These BPFs are adjusted by
variable capacitors (D402,D403,D404,D405 and D406). The
input voltage to the variable capacitor is regulated by
voltage output from the microprocessor (IC805).
2) First Mixer
The signal from the front end is mixed with the first local
oscillator signal generated in the PLL circuit by Q403 to
produce a first IF frequency of 49.95 MHz.
The resulting signal passes through the XF401 MCF to cut
the adjacent spurious and provide the opitimun
characteristics, such as adjacent frequency selectivity.
6

CIRCUIT DESCRIPTION

CF
450kHz
MCF
IF SYSTEM
AMP
49.95MHz
50.4MHz
X3 multiply
TCXO
RX: 390.05 ~ 420.05MHz (E)
420.05 ~ 462.05MHz (X2)
RF
PLL
MIC
AMP VCO
AMP
RF AMP MIXER
MCF
Q404 XF401
BPF Q403
TUNE 1st Local
IC601
IC605
AF VOL AF PA
AQUA
16.8MHz
3) IF Amplifier Circuit
The first IF signal is passed through a four-pole monolithic
crystal filter (XF401) to remove the adjacent channel signal.
The filtered first IF signal is amplified by the first IF amplifier
(Q202) and then applied to the lF system IC (IC401). 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 50.4MHz 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
(CF401) to remove the adjacent channel signal. The filtered
second IF signal is amplified by the limiting amplifier and
16.8MHz
demodulated by the quadrature detector with the ceramic
MIC
discriminator (CD401). 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 IC805, pin 54.
When a WIDE (low level) data is received, Q401 turn on.
IF AMP
When a NARROW (high level) data is received, Q401 turn
Q402
off.
Q401 turns off/on with the Wide/Narrow data and the IC401
detector output level is switched to maintain a constant
output level during wide or narrow signals.
SP
W/N
L : Wide
H : Narrow
Fig. 3 Wide/Narrow switching circuit
5) Audio Amplifier Circuit
The demodulated signal from IC401 is amplified by IC602,
and goes to AF amplifier through IC601.
The signal then goes through an AF volume control (VR801),
and is routed to an audio power amplifier (IC605) where it is
amplified and output to the speaker.
AFOUT
IFO
QUAD
C409
R408
Q401
CD401
R409
Q402
IC401
FM IF SYSTEM
5R