Yaesu FT-8900R, Technical Supplement, Page: 6 / 58

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first mixer Q1003 (
3SK296ZQ
). Meanwhile, the UHF lo-
cal signal from the UHF-VCO/B Q1106 (
2SC5006
) is de-
livered to first mixer Q1004 , yielding the 47.25 MHz
“Right” band first IF.
“Right” 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 “Right” band RF amplifier Q1007
(
3SK296ZQ
).
The amplified 144 MHz signal is passed through the var-
actor-tuned band-pass filter network consisting of D1016 ,
D1017 , D1018 (all
HVC365
) and associated circuitry to the
first mixer Q1008 (
3SK296ZQ
). Meanwhile, the VHF lo-
cal signal from the VHF-VCO/B Q1109 (
2SC5374
) is de-
livered to first mixer Q1008 , yielding the 47.25 MHz
“Right” band first IF.
“Right” Band IF and AF Signal
The 47.25 MHz “Right” band first IF is delivered to the
monolithic crystal filter XF1001 which strips away un-
wanted mixer products, then passed through the IF am-
plifier Q1017 (
2SC4400
) to the IF IC Q1018 (
TA31136FN
).
Meanwhile, a portion of the output of 11.7 MHz crystal
X1002 is multiplied fourfold by Q1026 (
2SC4400
) to pro-
vide the 46.8 MHz second local signal, then applied to the
IF IC Q1018 . Within the IF IC Q1018 , the 46.8 MHz sec-
ond local signal is mixed with the 47.25 MHz “Right” band
first local signal to produce the 450 kHz “Right” band sec-
ond IF.
The 450 kHz “Right” band second IF is delivered to the
ceramic filter CF1001 (
CFWM450E
) which strips away all
but the desired signal, then passed through the IF ampli-
fier within Q1018 to the ceramic discriminator CD1001
(
CDBM450C24
) which removes any amplitude variations
in the 450 kHz IF signal before detection of speech.
The demodulated “Right” band audio is passed through
the de-emphasis network, low-pass filter network (con-
sisting of Q1033 (
NJM2902V
) and associated circuitry) and
the high-pass filter network (consisting of Q1025
(
NJM2092V
) and associated circuitry). The filtered audio
signal is passed through the audio volume control IC Q1042
(
M511312FP
), which adjusts the audio sensitivity to com-
pensate 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.
Squelch Control
“Left” Band
When no carrier is being received on the “Left” band, noise
at the output of the detector stage in Q1024 is amplified
and band-pass filtered by the noise amp section of Q1024 .
The resulting DC voltage is delivered to pin 2 of main
CPU Q1084 (
M38268MCL
), which compares the squelch
threshold level to that which set by the front panel SQL
knob.
While no carrier is being received on the “Left” band, pins
43 and 45 of Q1084 remain “low,” to disable the audio
switch Q1046 / Q1047 , thus disabling the audio output from
the speaker.
“Right” Band
When no carrier is being received on the “Right” band,
noise at the output of the detector stage in Q1018 is am-
plified and band-pass filtered by the noise amp section of
Q1018 . The resulting DC voltage is delivered to pin 5 of
main CPU Q1084 , which compares the squelch threshold
level to that which set by the front panel SQL knob.
While no carrier is being received on the “Left” band, pins
42 and 44 of Q1084 remain “low,” to disable the audio
switch Q1046 and Q1047 , thus disabling the audio out-
put from the speaker.
Transmitter Signal Path
AF Signal
The speech signal from the microphone is passed through
the MIC jack J3003 to the AF amplifier Q3001 (
NJM2904V
)
on the PANEL-SUB UNT. The amplified speech signal is
passed through the panel separation jacks J3001 and J1005
to the MAIN Unit. On the MAIN UNIT, the speech signal
is delivered to the limiting amplifier Q1054 (
NJM2902V
)
to prevent over-modulation, then is delivered to a low-
pass filter network consisting of Q1054 and associated cir-
cuitry.
430 MHz Signal
The adjusted speech signal from Q1054 is passed through
transistor switch Q1051 (
BU4066BCFV
) to varactor di-
odes D1069 (
HVC375
) and D1070 (
HVC350B
), which fre-
quency modulate the transmitting VCO, made up of UHF-
VCO/B Q1106 (
2SC5006
) and D1071 (
HSC277
).
The modulated transmit signal is passed through buffer
amplifiers Q1107 , Q1108 , and Q1146 (all
2SC5006
) and
diode switches D1073 (
HSC277
) and D1128 (
DAN235E
)
to the pre-drive amplifier Q1139 (
2SK2596
).
The amplified transmit signal from Q1139 is passed
through diode switch D1134 (
HSC277
) and the driver
amplifier Q1137 (
2SK2975
) to the diode switch D1134
(
HSC277
), then finally amplified by power amplifier
Circuit Description