Kenwood TK-2107, Service Manual

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5
TK-2107
TK-260 :K, K2
1. Frequency configuration
The receiver utilizes double conversion. The first IF is
38.85MHz and the second IF is 450kHz. The first local
oscillator signal is supplied from the PLL circuit.
CIRCUIT DESCRIPTION
ANT
ANT SW
RF
AMP
MCF
CF
IF SYSTEM
AF
AMP
RX
TX
PA
AMP
TX
AMP
PLL
VCO
MIC
AMP
TCXO
X3
multiply
38.85MHz
450kHz
38.4MHz
12.8MHz
SP
MIC
Fig. 1 Frequency configuration
ANT
D102, D103
BPF
RF AMP
Q203 BPF
MIXER
Q202
MCF
XF200
IF AMP
Q201
CF200
IF, MIX, DET
IC200
AF AMP
LPF, HPF
IC300
AF PA AMP
IC302
SP
X3
multiply
Q1
TCXO
1st Local OSC
(PLL)
ANT SW
Fig. 2 Receiver section configuration
The PLL circuit in the transmitter generates the necessary
frequencies. Fig. 1 shows the frequencies.
2. Receiver
The receiver is double conversion superheterodyne,
designed to operate in the frequency range of 216 to 223MHz
(M3 type).
The frequency configuration is shown in Fig. 1.
1) Front - end RF amplifier
An incoming signal from the antenna is applied to an RF
amplifier (Q203) after passing through a transmit/receive
switch circuit (D102 and D103 are off) and a band pass filter
(L208, L209 and L210). After the signal is amplified (Q203),
the signal is filtered through a band pass filter (L203 and L214)
to eliminate unwanted signals before it is passed to the first
mixer. (See Fig. 2)
2) First Mixer
The signal from the RF amplifier is heterodyned with the
first local oscillator signal from the PLL frequency synthesizer
circuit at the first mixer (Q202) to create a 38.85MHz first
intermediate frequency (1st IF) signal. The first IF signal is
then fed through two monolithic crystal filters (MCFs : XF200)
to further remove spurious signals.
3) IF amplifier
The first IF signal is amplified by Q201, and then enters
IC200 (FM processing IC). The signal is heterodyned again
with a second local oscillator signal within IC200 to create a
450kHz second IF signal. The second IF signal is then fed
through a 450kHz ceramic filter (CF200) to further eliminate
unwanted signals before it is amplified and FM detected in
IC200.
4) AF amplifier
The recovered AF signal obtained from IC200 is amplified
by IC300 (1/4), filtered by the IC300 low-pass filter (2/4) and
IC300 high-pass filter (3/4) and (4/4), and de-emphasized by
R303 and C306. The processed AF signal passes through an
AF volume control and is amplified to a sufficient level to drive
a loud speaker by an AF power amplifier (IC302).