Alinco DR-235 TMkIII Service Manual page 4

5. Squelch Circuit
6. AIR Band Reception
7. WIDE/NARROW
Switching circuit
2 ) T r a n s m i t t e r S y s t e m D R - 2 3 5
1. Modulator Circuit
2. Power Amplifier Circuit
3. APC Circuit
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The detected output which is outputted from the pin 9 of IC108 is inputted
to pin 8 of IC108 after it was been amplified by 10120:A and it is outputted
from pin 14 after the noise component was been eliminated from the
composed band pass filter in the built in amplifier of the IC. 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 IC108, and is output from pin12 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 D115 and D116.
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:C and D consists of four operational amplifiers; one amplifier (pins
12, 13, and 14) is composed of pre-emphasis and IDC circuits and the
other (pins 8, 9, and 10) 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.
The transmitted signal is oscillated by the VCO, amplified by the drive
amplifier (Q145) and younger amplifier (Q115), and input to the final
power module (IC110). The signal is then amplified by the final power
module (IC110) and led to the antenna switch (D110) and low-pass filter
(L113, L114, L115, L116, C215, C216, C202, C203 and C204), where
unwanted high harmonic waves are reduced as needed, and the resulting
signal is supplied to the antenna.
Part of the transmission power from the low-pass filter is detected by
D111, converted to DC. The detection voltage is passed through the APC
circuit (IC114:A,IC114:B), then it controls the APC voltage supplied to the
younger amplifier Q115 and the final power module IC110 to fix the
transmission power.