Yaesu FT-2800M Technical Supplement page 8

Circuit Description
Transmitter
The speech signal from the microphone is delivered via
the MIC Jack to the RF Unit; after passing through Q315
(NJM2902V) which consists of amplifier, pre-emphasis,
limiter (IDC instantaneous deviation control) and lowpass
filter, to Q319 (M6364FP) which is adjusted for opti-
mum deviation level and delivered to the TX VCO Q322.
The speech signal from the microphone and CTCSS are
FM modulated by the TX VCO of the synthesizer, while
DCS audio is modulated by the reference frequency os-
cillator of the synthesizer.
Synthesizer output, after passing through diode switch
D311 (1SS321), is amplified by pri- drivers Q317
(2SC3356) and Q314 (RD00HVS1), driver Q313
(2SK3075), and power amplifier Q305 (RD70HVS1)
to obtain full RF output. The RF energy then passes
through antenna switch D303 (XB15A407) and a low-
pass filter circuit and finally to the antenna connector.
RF output power from the final amplifier is sampled by
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C318 and C324 and is rectified by D302 (1SS321).
The resulting DC is fed through Automatic Power Con-
troller Q309 (UMT1N), Q312 (DTC114), and Q311
(2SB1197) to transmitter RF amplifier Q305 and is used
to provide control of the power output.
Generation of spurious products by the transmitter is min-
imized by the fundamental carrier frequency being equal
to the final transmitting frequency, modulated directly in
the transmit VCO.
Additionally harmonic suppression is provided by a low-
pass filter consisting of L303, L305, C303, C309, C310,
and C316, resulting in more than 60 dB of harmonic sup-
pression prior to delivery of the RF