TM-V71A/V71E
4
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.
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.
Fig. 2 Band A and Band B VHF receiver circuit
ANT
SW
D/A
AIP
SW
D134,135
D186,188
LPF
RF AMP
Q228
RF AMP
Q227
IF AMP
Q495
X486
45.505MHz
MIXER
Q226
MCF
XF486
CF
Wide
IC576
Q229
BPF
D241~243
L248,249,258
BPF
D238~240
L245,257
BPF
D232~234
L232,236,250
BPF
D229~231
L232,233,260
CF
Narrow
IC667
SW
IC576
MPU
IC918
FM IC
IC486
1st Local OSC
Band A
Band B
2nd Local OSC
Band A
AF
D/A
AIP
SW
RF AMP
Q293
RF AMP
Q292
IF AMP
Q551
MIXER
Q291
MCF
XF546
CF
Wide
IC576
Q294
BPF
D306~308
L312~314
BPF
D303~305
L309,310,322
BPF
D297~299
L301,302,323
BPF
D294~296
L297,298,324
CF
Narrow
IC667
SW
IC577
MPU
IC918
FM IC
IC546
1st Local OSC
2nd Local OSC
Band B
AF
45.05MHz
49.95MHz
TCXO
X66
Tripler
x3
16.8MHz
Q547
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.
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.
CIRCUIT DESCRIPTION
