Service Manual Part 1
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Transmitter speech from the microphone is preamplified and fed into an automatic level
control circuit which also has three mute facilities (one for options and two for the
microprocessor). The speech is pre-emphasised and high pass filtered to reduce CTCSS
components. The speech passes via the RF PCB to the limiter on the TCXO/Tx audio
PCB.
The FFSK modem tones pass through a level potentiometer before being fed to the lim-
iter on the TCXO/Tx audio PCB. DCS/CTCSS signals are generated by the microproces-
sor and are filtered by a low pass filter before being passed to the level potentiometer on
the TCXO/Tx audio PCB.
Five tone Selcall and DTMF modules are both available to directly interface to the
microprocessor. Selcall tones are fed to the limiter on the TCXO/Tx audio PCB and
DTMF tones are summed at the automatic level control.
Receiver audio from the IF PCB passes through a low pass filter where it is split into sig-
nalling and speech paths. Five tone signals are coupled to the five tone module. DCS/
CTCSS passes through a low pass filter and limiter before arriving at the microproces-
sor. FFSK modem signals pass through a buffer amplifier before the modem input.
Speech is de-emphasised and passed through one or two high pass filters, depending on
what signalling is used. Processed speech passes through the mute to an amplifier
where speech and progress tones are summed. The signal then passes via the volume
control to the audio power amplifier, on the RF PCB.