Transmitter System - Alinco DR-135 Service Manual

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

2) Transmitter System

1. Modulator Circuit
4
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.)
When the frequency is within 118 ~ 135.995MHz, Q110 automatically turns
ON, pin 14 of IC108 becomes "L" level and the condition becomes in AM detec-
tion mode.
The receiver signal passed through the duplexer is let to the antenna switch
(D107, D101). After passing through the band-pass filter, the signal is amplified
by RF amplifier Q112. Secondly the signal is mixed with the signal from the first
local oscillator in the first-mixer Q106, then converted into the first IF . Its un-
wanted signal is let to IC106, pin24. Then converted into the second IF. and is
demodulated by AM decoder of IC106,and is output from pin13 as the AF
signal.
The 2nd IF 450 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 electric 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 fre-
quency modulation.