Circuit Description - Kenwood TK-3170 Service Manual

1. Frequency Configuration
The receiver utilizes double conversion. The first IF is
49.95MHz and the second IF is 450kHz. The first local oscil-
lator signal is supplied from the PLL circuit.
The PLL circuit in the transmitter generates the necessary
frequencies. Figure 1 shows the frequencies.
TX/RX : 450~490MHz
ANT
1st MIX
MCF
ANT RF
SW AMP
49.95MHz
400.05~
440.05MHz
RF
TX
AMP
AMP
450~490MHz
Fig. 1 Frequency configuration
2. Receiver System
The receiver system is shown in Figure 2.
2-1. Front End (RF AMP)
The signal coming from the antenna passes through the
transmit/receive switching diode circuit (D604, D605, D606
and D608), passes through a BPF (L717 and L718), and is
amplified by the RF amplifier (Q705).
The resulting signal passes through a BPF (L711, L712 and
L713) and goes to the mixer. These BPFs are adjusted by
variable capacitors (D703, D704, D705, D706 and D707). The
input voltage to the variable capacitor is regulated by voltage
output from the DC amplifier (IC19).
2-2. First Mixer
The signal from the front end is mixed with the first local
oscillator signal generated in the PLL circuit by Q704 to pro-
duce a first IF frequency of 49.95 MHz.
The resulting signal passes through the XF701 MCF to cut
the adjacent spurious and provide the optimum characteris-
tics, such as adjacent frequency selectivity.
2-3. IF Amplifier Circuit
The first IF signal is passed through a four-pole monolithic
crystal filter (XF701) to remove the adjacent channel signal.
ANT
BPF
ANT
SW
TUNE

CIRCUIT DESCRIPTION

CF
450kHz
SP
IF AF
VOL
SYSTEM AMP
50.4MHz
X3
TCXO 16.8MHz
multiply
MIC
PLL
MIC
VCO
AMP
Q705
RF Q704
BPF XF701
AMP 1st MIX
MCF Q703
IF AMP
TUNE 1st Local
Fig. 2 Receiver system
The filtered first IF signal is amplified by the first IF amplifier
(Q703) and then applied to the lF system IC (IC701). 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 out-
put (TCXO X501) and produces the second IF signal of
450kHz.
The second IF signal is passed through the ceramic filter
(Wide : CF701, Narrow : CF702) to remove the adjacent chan-
nel signal. The filtered second IF signal is amplified by the
limiting amplifier and demodulated by the quadrature detec-
tor with the ceramic discriminator (CD701). The demodu-
lated signal is routed to the audio circuit.
2-4. Wide/Narrow Switching Circuit
Wide and Narrow settings can be made for each channel
by switching the ceramic filters CF701 (Wide), CF702 (Nar-
row). The Wide and Narrow is output from IC4.
D701 and D702 are switched to ceramic filters when a
Wide/Narrow level is selected.
Q702 turns on/off with the Narrow and the IC701 detector
output level is changed to maintain a constant output level
during wide or narrow signals.
IC701
Narrow
Fig. 3 Wide/Narrow switching circuit
CF702
CF701
IC10
AF AMP
IC701
AQUA-L
IF, MIX, DET
Q701
X501
X3 multiply TCXO
16.8MHz
2nd Local
TK-3170/3173
Q702
R719
R717
R718
CD701 5C
Narrow
Wide
CF701
D702 D701
CF702
IC18
AF PA SP
IC13 IC16
VOL
AFOUT
23