Circuit Description - Kenwood TK-2160 Service Manual

1. Frequency Configuration
The receiver utilizes double conversion. The first IF is 49.95
M Hz 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 show s the frequencies.
ANT TX/RX: 136 ~ 174M Hz (K,M )
RF
ANT SW
AM P
49.95M Hz
RX: 185.95 ~ 233.95M Hz
TX: 136 ~ 174M Hz (K,M )
(K,M )
TX
AM P AM P
Fig. 1 Frequency configuration
2. Receiver
The frequency configuration of the receiver is shown in Fig. 2.
ANT
RF AM P
Q404
BPF
ANT SW
TUNE
CF401
IC602
AF Am p
IC401
IF,M IX,DET
X1
Q4
TCXO
16.8M Hz
X3 m ultiply
2nd Local
Fig. 2 Receiver section
1) Front End (RF AM P)
The signal coming from the antenna passes through the
transmit/receive sw itching diode circuit, (D204,D206,D208
and D212) passes through a BPF (L411 and L412), and is
amplified by the RF amplifier (Q404).
The resulting signal passes through a BPF (L407 and L409)
and goes to the mixer. These BPFs are adjusted by variable
capacitors (D402,D403,D404 and D405). The input voltage
to the variable capacitor is regulated by voltage output from
the microprocessor (IC805).
2) First M ixer
The signal from the front end is mixed w ith the first local
oscillator signal generated in the PLL circuit by Q403 to
produce a first IF frequency of 49.95 M Hz.
The resulting signal passes through the XF401 M CF to cut
t he adjacent spurious and provide t he opit im un
characteristics, such as adjacent frequency selectivity.

CIRCUIT DESCRIPTION

CF
450kHz
M CF
AF
IF SYSTEM
AM P
50.4M Hz
X3 m ultiply
TCXO
16.8M Hz
RF PLL
M IC
VCO
AM P
M IXER M CF IF AM P
XF401
BPF Q403
Q402
TUNE 1st Local
IC601
IC605
AF VOL AF PA
AQUA
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
(Q402) and then applied to the lF system IC (IC401). The
IF syst em IC provides a second m ixer, second local
oscillator, limiting amplifier, quadrature detector and RSSI
(Received Signal Strength Indicator). The second mixer
mixes the first IF signal w ith the 50.4M Hz of the second
SP
local oscillator output (TCXO X1) and produces the second
IF signal of 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
demodulated by the quadrature detector w ith the ceramic
M IC
discriminator (CD401). The demodulated signal is routed
to the audio circuit.
4) Wide/ Narrow Sw itching Circuit
Narrow and Wide settings can be made for each channel
by sw itching the demodulation level.
The WIDE (high level) and NARROW (low level) data is
output from IC805, pin 54.
When a WIDE (high level) data is received, Q401 turn off.
When a NARROW (low level) data is received, Q401 turn on.
Q401 turns on/off w ith the W ide/Narrow data and the
IC401 detector output level is sw itched to m aintain a
constant output level during w ide or narrow signals.
SP
AFOUT
Q401
W/N
H : Wide
L : Narrow
Fig. 3 Wide/ Narrow sw itching circuit
5) Audio Amplifier Circuit
The demodulated signal from IC401 is amplified by IC602,
and goes to AF amplifier through IC601.
The signal t hen goes t hrough an AF volum e cont rol
(VR801), and is routed to an audio pow er amplifier (IC605)
w here it is amplified and output to the speaker.
TK-2160
Q402
IC401
FM IF SYSTEM
QUAD IFO
C409
R408
CD401
R409
5R
7