Circuit Description; Outline; Receiver Circuit; Audio Amplifier - Kenwood TK-8180 Service Manual

TK-8180

1. Outline

The TK-8180 is a UHF/FM transceiver designed to operate
in the frequency range of 450 to 520MHz. Transmission out-
put power is 30 watts (490~520MHz : 25W). The maximum
channel capacity 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 450MHz to
520MHz.
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 HPF (D107, D108,
D109 and D110), RF amplifier Q103, and latter BPF (D103,
D104, D105 and D106). The BPF covers frequency ranges
450 to 520MHz.
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 (X57-699)
IF AMP
Q172
XF171
RSSI
DET
NOISE DET
SQL
16

CIRCUIT DESCRIPTION

44.85MHz
IF AMP
1st MIX DBM
Q171
MCF MCF
XF171
(2/2) (1/2)
FM SYSTEM IC : IC172
Q178
QUD
SW
W/N
NOISE
AMP
Q175
D173
DET
SW
D172
CFSW
IC407 IC410
DAC DEO
IC404
ASQ
AMP
CPU
IC412 (B/2)
RSSI
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
IC171 D103~D106
LPF
Buff AMP
Q313
CF172
X171
(Wide)
44.395MHz
CF171
SW
(Narrow)
D171
CFSW
455kHz
IC413 IC415
AQUA
SW
-L
AFO
Receiver circuit
450~520MHz
HPF
Q103
D107~D110
Q306
RX VCO
Buff AMP
Q311
f –44.85MHz
RX
405.15~475.15MHz
IC410 IC417
Q419
AF
DAC MUTE
AMP
RX ANT
INT. SP