RMU800A SERVICE MANUAL
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2.3 IF Amplifier
The first IF signal is amplified by Q125, Q118 and then enters IC119
（
TA31136FN
）
. The signal is mixed
with the second local oscillator signal (73.05MHz) to create a 450KHz second IF signal. The second IF
signal is then fed to a ceramic filter (N: CF101, CF103; W: CF102, CF104) to eliminate unwanted signals.
The resulting signal is detected by IC119 and output from Pin9 as an AF signal.
2.4 AF Amplifier
The AF signal from IC119 is amplified by IC109 before being filtered. The resulting AF signal passes
through Q108
（
AF MUTE
）
and IC121(electronic switch) , then is amplified by IC106 ( the received
signalling is inputted into CPU for decoding) and IC104. The amplified signal is fed to IC125 (volume
control) and Q114 (SP MUTE) before entering AF AMP (IC126). The outputted AF signal is then delivered
to the speaker through control panel.
2.5 Squelch
The AF signal from IC119 is amplified by IC109 again, and then filtered to remove noise signals. The
noise signal is amplified by Q121 and rectified by D110 to produce an ASQ level. The ASQ level is then
compared in CPU (IC120) to generate a level which controls AF MUTE and SP MUTE. IC120 determines
whether to output sounds from the speaker by controlling Q108, Q114.
3. Transmitter Circuit
Figure 2 Transmitter Section Configuration
3.1 MIC Circuit and Modulation Circuit
The AF signal from MIC is amplified by IC104 after passing through the MIC control switch (Q507). The
resulting signal is then amplified by IC106 and pre-emphasized, encoded. It is passed to IC121
(electronic switch) before reaching IC125. The signalling is inputted into IC125 and enters VCO for
modulation.
