Yaesu FT-7100M, Technical Supplement, Page: 6 / 68

6
Circuit Description
The detected audio passes through the de-emphasis
network, a high-pass filter consisting of Q1117
( M5223AGP-1 ) and associated circuitry, and a low-pass
filter consisting of Q1117 ( M5223AGP-2 ) and associated
circuitry. The filtered audio signal is amplified by Q1046
( NJM2902V-3 ), then passes through the audio volume
control IC Q1096 ( M511312FP ), which adjusts the audio
sensitivity to compensate for audio level variations, and
then is delivered to audio switch
Q1094 ( BU4053BCFV ).
When the internal speaker is selected, the audio signal
is amplified by Q1098 ( TDA7233D ) then applied to the
internal loudspeaker. When the external speaker is select-
ed, the audio signal is amplified by
Q1097 ( TDA2003H ),
then it passes through the EXT SP jack to the external
loudspeaker.
V/V (VHF-VHF) Dual Reception
During V&V operation, the incoming VHF "sub" band
signal is passed through a low-pass filter network, anten-
na switching diode D1056 (1SS355), D1057 (RLS135) and
a high-pass filter network to the RF amplifier Q1007
(3SK131). The amplified RF signal is passed through a
high-pass filter network, VHF "sub" RF amplifier Q1013
(2SC3120), and a low-pass filter network, then is applied
to the VHF "sub" first mixer Q1015 (2SC3120) along with
the 255 MHz VHF "sub" first local signal from the PLL
circuit.
The 399 ~ 403 MHz VHF "sub" first IF signal is applied
to the VHF "sub" second IF mixer Q1019 ( 3SK228 ) along
with the VHF "sub" second local signal from the PLL cir-
cuit. The VHF "sub" second local signal is generated be-
tween 444.05 MHz and 448.05 MHz by the UHF VCO
Q1023 .
The 45.05 MHz VHF "sub" second IF signal is applied
to the UHF receiving circuit. The VHF "sub" signal is am-
plified, filtered, and demodulated, etc., by the UHF "main"
receiving circuit, described previously.
U/U (UHF-UHF) Dual Reception
During U/U operation, the incoming UHF "sub" band
signal is passed through high-pass and low-pass filter
networks, antenna switching diodes
D1058 ( 1SS355 ) and
D1059 ( RLS135 ), and another high-pass filter network to
the RF amplifier Q1009 ( 2SC3120 ). The amplified RF sig-
nal is passed through a low-pass filter network, UHF "sub"
RF amplifier
Q1014 ( 2SC3120 ), and low-pass filter net-
work, then is applied to the UHF "sub" first mixer Q1016
( 2SC3120 ) along with the 255 MHz UHF "sub" first local
signal from the PLL circuit.
The 175 ~ 195 MHz UHF "sub" first IF signal is applied
to the UHF "sub" second IF mixer Q1023 ( 3SK228 ) along
with the UHF "sub" second local signal from the PLL cir-
cuit. The UHF "sub" second local signal is generated be-
tween 153.30 MHz and 173.30 MHz by the VHF VCO
Q1025.
The 21.7 MHz UHF "sub" second IF signal applied to
VHF receiving circuit. The UHF "sub" signal is amplified,
filtered, and demodulated, etc., by the VHF receiving cir-
cuit, described previously.
VHF Squelch Control
When no VHF carrier is being received, noise at the
output of the detector stage in Q1043 is amplified and
band-pass filtered by the noise amp section of Q1043 , then
passes through the noise amplifier Q1051 ( 2SC4154E ) to
noise detector D1034 ( MC2850 ). The resulting DC volt-
age is applied to pin 93 of main CPU Q 1 0 7 5
( M30620ECGP ), which compares the squelch threshold
level to that which set by the front panel VHF SQL knob.
While no carrier is received, pin 76 of Q1075 remains
"high," turning on the squelch switch Q1076 ( RT1N241M )
to disable audio output from the speaker.
UHF Squelch Control
When no UHF carrier is being received, noise at the
output of the detector stage in Q1034 is amplified and
band-pass filtered by the noise amp section of Q1034 , then
passes through the noise amplifier Q1052 ( 2SC4154E ) to
noise detector D1030 ( MC2850 ). The resulting DC volt-
age is applied to pin 89 of main CPU Q1075 , which com-
pares the squelch threshold level to that which set by the
front panel UHF
SQL knob.