Receiver System; Band A/B Vhf Receiver Circuit; Band A/B Uhf Receiver Circuit - Kenwood TM-V71A Service Manual

TM-V71A/V71E

2. Receiver System

2-1. Band A VHF Receiver Circuit
The incoming signal from the antenna passes through
a filter circuit and goes to the RF amplifier (Q228). The
amplifi ed signal enters the band-pass fi lter. After the signal
passes through the band-pass fi lter, it is amplifi ed by another
RF amplifier (Q227) and then passes through the band-
pass fi lter before entering the mixer (Q226). The frequency
of the signal is converted by the fi rst local oscillator (Upper
heterodyne) to generate a 45.05MHz first IF signal. The
signal passes through the MCF (XF486), is amplifi ed by the
IF amplifi er (Q495) and then enters the FM IC (IC486).
The signal is converted to the 455kHz second IF signal
by the second local oscillator (Upper heterodyne). It is then
detected to generate an audio signal.
D134,135 RF AMP
LPF D186,188 Q228
ANT
SW
RF AMP
Q293
2-3. Band A UHF Receiver Circuit
The incoming signal from the antenna passes through
a filter circuit and goes to the RF amplifier (Q363). The
amplified signal enters the band-pass filter. After the
signal passes through the band-pass filter, it is amplified
by another RF amplifier (Q362) and then passes through
the band-pass filter before entering the mixer (Q361).
The frequency of the signal is converted by the fi rst local
oscillator (Lower heterodyne) to generate a 45.05MHz fi rst
IF signal. The signal passes through the MCF (XF486), is
amplifi ed by the IF amplifi er (Q495) and then enters the FM
IC (IC486). The signal is converted to the 455kHz second IF
signal by the second local oscillator (Upper heterodyne). It is
then detected to generate an audio signal.
4
CIRCUIT DESCRIPTION
BPF BPF
D241~243 D238~240 RF AMP
L248,249,258 L245,257 Q227
IC667
AIP
MPU D/A
SW
IC918 IC576
IC576
Q229
SW
BPF BPF
D306~308 D303~305
RF AMP
L312~314 L309,310,322
Q292
IC667
AIP
MPU D/A
SW
IC918 IC577
IC576
Q294
SW
Fig. 2 Band A and Band B VHF receiver circuit
2-2. Band B VHF Receiver Circuit
The incoming signal from the antenna passes through
a filter circuit and goes to the RF amplifier (Q293). The
amplifi ed signal passes through the band-pass fi lter and is
amplified by another RF amplifier (Q292). It then passes
through the band-pass fi lter and goes to the mixer (Q291).
The frequency of the signal is converted by the fi rst local
oscillator (Upper heterodyne) to generate a 49.95MHz fi rst
IF signal. The signal passes through the MCF (XF546), is
amplified by the IF amplifier (Q551) and then enters the
FM IC (IC546). The signal is then converted to the 450kHz
second IF signal by the second local oscillator, which is
tripled 16.8MHz (Upper heterodyne). It is then detected to
generate an audio signal.
BPF BPF
D232~234 D229~231 MIXER
L232,236,250 L232,233,260 Q226
1st Local OSC
Band A
BPF BPF
D297~299 D294~296
MIXER
L301,302,323 L297,298,324
Q291
1st Local OSC
Band B
2-4. Band B UHF Receiver Circuit
The incoming signal from the antenna passes through
a filter circuit and goes to the RF amplifier (Q408). The
amplifi ed signal passes through the band-pass fi lter and is
amplified by another RF amplifier (Q407). It then passes
through the band-pass fi lter and goes to the mixer (Q406).
The frequency of the signal is converted by the fi rst local
oscillator (Lower heterodyne) to generate a 49.95MHz fi rst
IF signal. The signal passes through the MCF (XF546), is
amplified by the IF amplifier (Q551) and then enters the
FM IC (IC546). The signal is then converted to the 450kHz
second IF signal by the second local oscillator, which is
tripled 16.8MHz (Upper heterodyne). It is then detected to
generate an audio signal.
The VHF/ UHF band-pass filter is tuned to the desired
frequency according to the BPF voltage output from the D/A
IC (IC667), and is controlled by the MPU (IC918) and the
varicap.
X486
45.505MHz
MCF IF AMP
2nd Local OSC
XF486 Q495
FM IC
IC486
45.05MHz
CF
Wide
CF
Narrow
16.8MHz Q547
TCXO Tripler
X66 x3
MCF IF AMP
XF546 Q551
FM IC
IC546
49.95MHz
CF
Wide
CF
Narrow
Band A
AF
2nd Local OSC
Band B
AF