Transmitter System (Dr-235) - Alinco DR-235 Service Manual

4. Audio Circuit
5. Squelch Circuit
6. AIR Band Reception(T only)
7. WIDE/NARROW switching circuit

5) Transmitter System (DR-235)

1. Modulator Circuit
The audio signal from pin 12 of IC108 is amplified by the audio amplifier
(IC104:A), and switched by the signal switch IC (IC111) and then input it to the
de-emphasis circuit.
and is compensated to the audio frequency characteristics in the de-emphasis
circuit (R203, R207, R213, R209, C191, C218, C217) and amplified by the AF
amplifier (IC104:D). The signal is then input to volume (VR1) . The adjusted
signal is sent to the audio power amplifier (IC117) through pin 1 to drive the
speaker.
The detected output which is outputted from the pin 12 of IC108 is inputted to
pin 19 of IC108 after it was been amplified by IC104:A and it is outputted from
pin 20 after the noise component was been eliminated from the composed
band pass filter in the built in amplifier of the IC, then the signal is rectified by
D106 to convert into DC component. The adjusted voltage level at VR101 is
delivered to the comparator of the CPU.
The voltage is led to pin 2 of CPU and compared with the setting voltage. The
squelch will open if the input voltage is lower than the setting voltage.
During open squelch, pin 30 (SQC) of the CPU becomes "L" level, AF control
signal is being controlled and sounds is outputted from the speaker.)
If it is made air band receiving mode, IF signal is demodulated by AM decoder
of IC106, and is output from pin13 as the AF signal.
The 2nd IF 455 kHz signal which passes through filter FL101 (wide) and FL102
(narrow) during narrow, changes its width using the width control switching
IC103 and IC102.
The audio signal is converted to an electrical signal by the microphone, and
input it to the microphone amplifier (Q6). Amplified signal which passes through
mic-mute control IC109 is adjusted to an appropriate mic-volume by means of
mic-gain adjust VR106.
IC114:A and B consists of two operational amplifiers; one amplifier (pins 1, 2,
and 3) is composed of pre-emphasis and IDC circuits and the other (pins 5, 6,
and 7) is composed of a splatter filter. The maximum frequency deviation is
obtained by VR107. and input to the signal switch (IC113) (9600 bps packet
signal input switch) and input to the cathode of the varicap of the VCO, to
change the electric capacity in the oscillation circuit. This produces the frequency
modulation.
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