Circuit Description - Kenwood TK-3180 Service Manual

1. Overview
This transceiver is UHF/FM portable transceiver designed
to operate in the frequency range of 450 to 520MHz.
2. Circuit Configuration by Frequency
The receiver is a double-conversion superheterodyne with
a first intermediate frequency (IF) of 59.85MHz and a second
IF of 455kHz. Incoming signals from the antenna are mixed
with the local signal from the PLL to produce the first IF of
59.85MHz.
This is then mixed with the 59.395MHz second local oscil-
lator output to produce the 455kHz second IF. This is de-
tected to give the demodulated signal.
The transmit signal frequency is generated by the PLL
VCO, and modulated by the signal from the microphone. It is
then amplified and sent to the antenna.
TX/RX : 450~520MHz
ANT
1st MIX
MCF
RF
ANT
SW AMP
59.85MHz
390.15~
460.15MHz
PA TX
AMP
AMP
450~520MHz
Fig. 1 Frequency configuration
ANT
L215
L111,112
L113 L216
ANT
SW
D106,107 BPF
D213,214
Q605
IC607
(1/2)
AQUA-L
SW
AM2

CIRCUIT DESCRIPTION

CF
455kHz
SP
FM IF AF
SYSTEM AMP
59.395MHz
MIC
PLL
MIC
VCO
AMP
Q207 L210
L211
RF Q206
XF200
AMP L212 1st MIX
BPF MCF
1st Local
OSC (PLL)
IC609
AF PA
IC605
Q618
VOL SW
VC1
SSW
VC2
Fig. 2 Receiver section
3. Receiver System
3-1. RF unit
An incoming RF signal from the antenna terminal is
passed through the antenna switch (D106, D107 and D213
are off) and then the bandpass filter (L215, L216). The
bandpass filter is adjusted by a variable capacitor. The input
voltage to the variable capacitor is regulated by the voltage
output from the D/A converter (IC605). The signal is ampli-
fied by RF amplifier (Q207), and passed through the band-
pass filter (L210, L211, L212).
The resulting signal is applied to the first mixer (Q206),
where it is mixed with the first local oscillator signal output
from the frequency synthesizer to produce the first IF
(59.85MHz).
3-2. IF unit
The first IF signal is passed through a four-pole monolithic
crystal filter (XF200) to remove a adjacent channel signal. The
filtered first IF signal is amplified by the first IF amplifier
(Q205) and then applied to the lF system IC (IC200). 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 59.395MHz of second local oscillator output
(crystal unit X200) and produces the second IF signal of
455kHz.
The second IF signal is passed through the ceramic filter
(CF201 : Wide, CF200 : Narrow) to more remove the adjacent
channel signal. The filtered second IF signal is amplified by
the limiting amplifier and demodulated by the quadrature de-
tector with ceramic discriminator (CD200). The demodulated
signal is routed to the audio circuit.
Q205
IF AMP
IC200
MIX, DET, IF
X200
CF200
2nd local
OSC
CF201
INT. SP
EXT. SP
TK-3180
IC600 (1/2)
AF AMP
Q203 IC606
SW SW HSDO
DMUTE
7