Alinco DR-135, Service Manual

Page: 10 / 71

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5. Squelch Circuit
The detected output which is outputted from the pin 11 of IC108 is inputted to
pin 13 of IC108 after it was been amplified by IC104: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, 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.
6. WIDE/NARROW switching circuit
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.
8) Transmitter System (DR-435)
1. Modulator Circuit
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.
2. Power Amplifier Circuit
The transmitted signal is oscillated by the VCO, amplified by the drive amplifier
(Q131, Q125) 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 (L116, L114, L115, C215,
C216, C202, C203 and C204), where unwanted high harmonic waves are
reduced as needed, and the resulting signal is supplied to the antenna.
3. APC Circuit
Part of the transmission power from the low-pass filter is detected by D111 and
D112, converted to DC. The detection voltage is passed through the APC
circuit(Q118, Q117, Q116), then it controls the APC voltage supplied to the
younger amplifier Q115 and the final power module IC110 to fix the transmission
power.