Transmitter Signal Path; Squelch Control - Yaesu FT-8800R Technical Supplement

Circuit Description
Meanwhile, a portion of the output of 11.7 MHz crystal
X1003 is multiplied fourfold by Q1043 (2SC4400) to pro-
vide the 46.8 MHz second local signal, then applied to the
IF IC Q1047. Within the IF IC Q1047, the 46.8 MHz second
local signal is mixed with the 47.25 MHz "Sub" band first
local signal to produce the 450 kHz "Sub" band second IF.
The 450 kHz "Sub" band second IF is delivered to the
ceramic filter CF1003 (CFWM450E) which strips away all
but the desired signal, then passed through the IF ampli-
fier within Q1047 to the ceramic discriminator CD1002
(CDBM450C24) which removes any amplitude variations
in the 450 kHz IF signal before detection of speech.
The demodulated "Sub" band audio is passed through the
de-emphasis network, audio switch D1048 (DAN222),
low-pass filter network (consisting of Q1053 (NJM2902V)
and associated circuitry) and the high-pass filter network
(consisting of Q1054 (NJM2904V) and associated circuit-
ry). The filtered audio signal is passed through the audio
volume control IC Q1063 (M511312FP), which adjusts the
audio sensitivity to compensate for audio level variations,
then is delivered to the audio switch Q1066 and Q1067
(both TC4W66FU).
When the internal speaker is selected, the audio signal is
amplified by Q1069 (TDA7233D) then applied to the in-
ternal loudspeaker. When the external speaker is select-
ed, the audio signal is amplified by Q1068 (LA4425A),
then it passes through the EXT SP jack to the external loud-
speaker.

Squelch Control

"Main" Band
When no carrier is being received on the "Main" band,
noise at the output of the detector stage in Q1044 is am-
plified and band-pass filtered by the noise amp section of
Q1044. The resulting DC voltage is delivered to pin 5 of
main CPU Q1104 (M38268MCL), which compares the
squelch threshold level to that which set by the front pan-
el SQL knob.
While no carrier is being received on the "Main" band,
pin 2 of Q1105 remain "low," to disable the audio output
from the speaker.
"Sub" Band
When no carrier is being received on the "Sub" band, noise
at the output of the detector stage in Q1047 is amplified
and band-pass filtered by the noise amp section of Q1047.
The resulting DC voltage is delivered to pin 2 of main
CPU Q1104, which compares the squelch threshold level
to that which set by the front panel SQL knob.
While no carrier is being received on the "Right" band,
pin 15 of Q1105 remain "low," to disable the audio out-
put from the speaker.
8

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 Q1074 (NJM2902V) to
prevent over-modulation, then is delivered to a low-pass
filter network consisting of Q1074 and associated circuitry.
430 MHz Signal
The adjusted speech signal from Q1074 is passed through
transistor switch Q1114, Q1115 (both DTC144EE) to var-
actor diodes D1079 (HVC375B) and D1080 (HVC350B),
which frequency modulate the transmitting VCO, made
up of UHF-VCO/B Q1116 (2SC5006) and D1081
(HSC277).
The modulated transmit signal is passed through buffer
amplifiers Q1117, Q1118 and Q1119 (all 2SC5006) and
diode switches D1099, D1101 (both HSC277) to the pre-
drive amplifier Q1132 (2SK2596).
The amplified transmit signal from Q1132 is passed
through diode switch D1106 (HSC277) and the driver am-
plifier Q1134 (RD07MVS1) to the diode switch D1107
(HSC277), then finally amplified by power amplifier
Q1135 (RD70HVF1), providing up to 35 Watts of power
output. These three stages of the power amplifier's gain
are controlled by the APC circuit.
The 35-Watt RF signal is passed through a high-pass fil-
ter network to the antenna switch D1118, D1119, and
D1120 (all UM9957F), then passed through a low-pass
filter network and another high-pass filter network to the
ANT jack.
144 MHz Signal
The adjusted speech signal from Q1074 is passed through
the transistor switch Q1114, Q1115 (both DTC144EE) to
varactor diodes D1082 and D1085 (both HVC365), which
frequency modulate the transmitting VCO, made up of
VHF-VCO/B Q1120 (2SC5374) and D1083 (HVC131).
The modulated transmit signal is passed through buffer
amplifiers Q1121 and Q1122 (both 2SC5374) and diode
switches D1089 and D1102 (both HSC277) to the pre-drive
amplifier Q1132 (2SK2596).
The amplified transmit signal from Q1132 is passed
through the diode switch D1105, D1106 (both HSC277)
and the driver amplifier Q1134 (RD07MVS1) to diode
switch D1108 (RLS135), then finally amplified by power
amplifier Q1135 (RD70HVF1) up to 50 Watts of power
output. These three stages of the power amplifier's gain
are controlled by the APC circuit.