Receiver System - Kenwood TM-V708A Service Manual

TM-V708A

2. Receiver system

2-1. Main VHF Receiver
The incoming signal from the antenna passes through a
filter circuit and goes to the RF amplifier (Q205). The
amplified signal enters the helical resonator (L209, L207,
L204). The helical resonator is tuned to the desired frequency
according to the BPF voltage output from the CPU with the
varicap (D206, D205, D202). After the signal passes through
a filter, it is amplified by another RF amplifier (Q202) and goes
to the single balanced mixer (Q200, Q201). The frequency of
ANT
LPF
2-2. Main UHF Receiver
The incoming signal from the antenna passes through a
filter circuit and enters the RF amplifier (Q508). The amplified
signal passes through the SAW filter (L517), is amplified by
another RF amplifier (Q505). Then it passes through the LC
filter (L508) and enters the single balanced mixer (Q501,
Q502). The frequency of the signal is converted by the first
ANT
HPF LPF
4
CIRCUIT DESCRIPTION
RF AMP BPF RF AMP
Q202
Q205
3SK239A
3SK239A
L209,L207,L204
D206
D205
D202
TUNE BY VOLTAGE
CPU
Fig. 2 Main VHF Receiver circuit
RF AMP RF AMP
SAW FILTER
Q505
Q508
2SK1875
3SK239A
(V)
L517
Fig. 3 Main UHF Receiver circuit
the signal is converted by the first local oscillator (Upper
heterodyne) to generate a 38.85MHz first IF signal. The signal
passes through the MCF (XF100), is amplified by the IF
amplifier (Q112) and enters the IF IC (IC100). Then the signal
is converted to the 450kHz second IF signal by the second
local oscillator, which is tripled 12.8MHz (Lower heterodyne).
Then it is detected to generate an audio signal.
SINGLE BALANCED
IF AMP
MIXER MCF
Q112
Q200,201
2SC5108
2SK302
(GR)
XF100
LO
local oscillator (Lower heterodyne) to generate a 45.05MHz
first IF signal. The signal passes through the MCF (XF400), is
amplified by the IF amplifier (Q406) and enters the IF IC
(IC400). The signal is converted to the 455kHz second IF
signal by the second local oscillator (Upper heterodyne). Then
it is detected to generate an audio signal.
SINGLE BALANCED
MIXER
LC BPF MCF
Q501,502
2SK302
(GR)
L508 XF400
LO
IF IC
IC100
AF
(Y)
CF
38.4MHz
Q102
2SC4649 X3
(N.P)
12.8MHz
IF AMP
IF IC
Q406
IC400
2SC5108
(Y)
CF
45.505MHz
AF