Circuit Description; Receiver Signal Path; “Left” Band Signals; “Right” Band Signals - Yaesu FT-8900R Technical Supplement

Receiver Signal Path

"Left" Band 430 MHz Signal
The 430 MHz signal is passed through a high-pass filter
network and a low-pass filter network to the antenna
switch diodes D1001/D1002 (both RLS135), then passed
through another low-pass filter network to the "Left" band
RF amplifier Q1001 (3SK296ZQ).
The amplified 430 MHz signal is passed through the band
switch D1008 (HSC277) to the varactor-tuned band-pass
filter network consisting of D1009, D1010, D1011 (all
HVC358B) and associated circuitry, then applied to the
first mixer Q1004 (3SK296ZQ). Meanwhile, the UHF lo-
cal signal from the UHF-VCO/A Q1112 (2SC5006) is de-
livered to first mixer Q1004, yielding the 45.05 MHz "Left"
band first IF.
"Left" Band 144 MHz Signal
The 144 MHz signal is passed through a low-pass filter
network and a high-pass filter network to the antenna
switching relay RL1001 (G5A-237P), then passed through
another high-pass filter network and low-pass filter net-
work to the "Left" band RF amplifier Q1006 (3SK296ZQ).
The amplified 144 MHz signal is passed through a varac-
tor-tuned band-pass filter network consisting of D1019,
D1020, D1021 (all HVC365) and associated circuitry to the
first mixer Q1010 (3SK296ZQ). Meanwhile, the VHF lo-
cal signal from the VHF-VCO/A Q1115 (2SC5374) is de-
livered to first mixer Q1010, yielding the 45.05 MHz "Left"
band first IF.
"Left" Band 50 MHz Signal
The 50 MHz signal is passed through a low-pass filter
network and antenna switching relay RL1003 (G5A-237P),
then passed through another low-pass filter network, an-
tenna switch relay RL1002 (G5A-237P), and band switch
diode D1144 (HSC277) to yet another low-pass filter net-
work, then applied to the "Left" band RF amplifier Q1006
(3SK296ZQ).
The amplified 50 MHz signal is passed through a band-
pass filter network and band switch diode D1027
(HSC277) to the first mixer Q1015 (3SK296ZQ). Mean-
while, the 50 MHz local signal from the RX50-29-VCO
Q1121 (2SC5374) is delivered to first mixer Q1015, yield-
ing the 45.05 MHz "Left" band first IF.
"Left" Band 28 MHz Signal
The 28 MHz signal is passed through a low-pass filter
network and antenna switching relay RL1003 (G5A-237P),
then passed through another low-pass filter network, an-
tenna switching relay RL1002 (G5A-237P) and band
switch diode D1144 (HSC277) to yet another low-pass fil-
ter network, then delivered to the "Left" band RF ampli-
fier Q1012 (2SC5374).

Circuit Description

The amplified 28 MHz signal is passed through a band-
pass filter network and band switch diode D1028
(HSC277) to the first mixer Q1015 (3SK296ZQ). Mean-
while, the 28 MHz local signal from the RX50-29-VCO
Q1121 is delivered to first mixer Q1012, yielding the 45.05
MHz "Left" band first IF.
"Left" Band IF and AF Signals
The 45.05 MHz "Left" band first local signal is delivered
to the monolithic crystal filter XF1002 which strips away
unwanted mixer products, then is passed through IF am-
plifier Q1019 (2SC4400) to the IF IC Q1024 (TA31136FN).
Meanwhile, a portion of the output of 11.15 MHz crystal
X1003 is multiplied fourfold by Q1027 (2SC4400) to pro-
vide the 44.6 MHz second local signal, then delivered to
the IF IC Q1024. Within the IF IC Q1024, the 44.6 MHz
second local signal is mixed with the 45.05 MHz "Left"
band first local signal to produce the 450 kHz "Left" band
second IF.
The 450 kHz "Left" band second IF is passed through the
filter switch D1033/D1034 (both DAN235E) to the ceram-
ic filter CF1002 (CFWM450E) which strips away all but
the desired signal, then it passes through the IF amplifier
within Q1024 to the ceramic discriminator CD1002
(CDBM450C24), which removes any amplitude variations
in the 450 kHz IF signal before detection of speech.
The demodulated "Left" band audio is passed through
the de-emphasis network, audio switch D1035 (DAN222),
low-pass filter network (consisting of Q1034 (NJM2902V)
and associated circuitry), and a high-pass filter network
(consisting of Q1025 (NJM2092V) and associated circuit-
ry). The filtered audio signal is passed through the audio
volume control IC Q1042 (M511312FP), which adjusts the
audio sensitivity to compensate for audio level variations,
then is delivered to the audio switch Q1046 and Q1047
(both TC4W66FU).
When the internal speaker is selected, the audio signal is
amplified by Q1050 (TDA7233D) then applied to the in-
ternal loudspeaker. When the external speaker is select-
ed, the audio signal is amplified by Q1045 (LA4425A),
then it passes through the EXT SP jack to the external loud-
speaker.
"Right" Band 430 MHz Signal
The 430 MHz signal is passed through a high-pass filter
network and a low-pass filter network to the antenna
switch diodes D1001/D1002, then passed through anoth-
er low-pass filter network to the "Right" band RF ampli-
fier Q1002 (3SK296ZQ).
The amplified 430 MHz signal is delivered through the
band switch D1008 (HSC277) to the varactor-tuned band-
pass filter network consisting of D1004, D1005, D1006 (all
HVC358B) and associated circuitry, then applied to the
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