Circuit Description - Kenwood TK-7180 Service Manual

1. Outline
The TK-7180/7189 is a VHF/FM transceiver designed to
operate in the frequency range of 136 to 174MHz. Transmis-
sion output power is 25 watts. The maximum channel capac-
ity is 512.
The unit consists of receiver, transmitter, phase-locked
loop (PLL) frequency synthesizer, and control circuits.
2. Receiver Circuit
The receiver is double conversion superheterodyne, de-
signed to operate in the frequency range of 136MHz to
174MHz.
The receiver circuit consists of the following : 2-1 front-
end circuit, 2-2 first mixer, 2-3 IF amplifier circuit, 2-4 audio
amplifier circuit, and 2-5 squelch circuit.
2-1. Front-end Circuit
The front-end circuit consists of former BPF (D11), RF am-
plifier Q103, and latter BPF (D103, D104, D105 and D106).
The BPF covers frequency ranges 136 to 174MHz.
The latter BPF (D103, D104, D105 and D106) attenuates
the unwanted signals, and sends only the necessary signal to
the first mixer.
TX-RX UNIT (X57-698)
IF AMP
Q172
MCF
XF171
(2/2)
RSSI
Q178
SW
W/N
DET
NOISE DET
D173
SQL
DET
IC407
ASQ
RSSI

CIRCUIT DESCRIPTION

44.85MHz
IF AMP
1st MIX DBM
Q171
MCF IC171
XF171
(1/2)
FM SYSTEM IC : IC172
QUD
CF172
NOISE
(Wide)
AMP
Q175
CF171
SW
(Narrow)
D172
CFSW
IC410
455kHz
DAC DEO
IC413
SW
IC404
AMP
CPU IC412 (B/2)
Fig. 1
2-2. First Mixer
The signal from the BPF is heterodyned with the first local
oscillator signal from the PLL frequency synthesizer circuit at
the first mixer DBM (IC171) to become a 44.85MHz first in-
termediate frequency (IF) signal. The first IF signal is fed
through a monolithic crystal filter (XF171) to further remove
spurious signals.
2-3. IF Amplifier
The first IF signal is amplified by Q171 and Q172, and then
enters IC172 (FM system IC). The signal is heterodyned
again with a second local oscillator signal (44.395MHz) with
in IC172 to become a 455kHz second IF signal. The second
IF signal is fed through a 455kHz ceramic filters (CF172;
Wide, CF171; Narrow) to further eliminate unwanted signal,
and the quadrature detection circuit FM-detects the signal to
produce a base-band signal and output it from pin 9.
2-4. Audio Amplifier
The demodulated audio signal from IC172 goes to IC415
through the AF amplifier (IC412) and IC413. The audio signal
goes to an electronic volume (IC410) and is amplified to drive
a loudspeaker by an audio power amplifier (IC417). The audio
output can be provided to external 4Ω speaker through the
speaker jack output (J401) on the rear panel. Q419 is a mute
switch.
RF AMP
BPF
Q103
D103~D106
LPF
Buff AMP Buff AMP
Q313
Q311
f +44.85MHz
RX
180.85~218.85MHz
X171
44.395MHz
SW
D171
CFSW
IC415 IC410
AQUA
DAC
-L
AFO
Receiver circuit
TK-7180/7189
136~174MHz
RX ANT
BPF
D11
Q306
RX VCO
TK-7180
model only
IC417 INT. SP
Q419
AF
MUTE
AMP
19