Driver Unit; Control Circuit - Icom IC-25A Instruction Manual

in the PLL unit to become the local oscillator signal for the transmitter and receiver, and to get а
DC-voltage to control the frequency of the VCO.
DRIVER UNIT
CLOCK PULSE GENERATE CIRCUIT
The input data for the microcomputer, is controlled by a custom-made LS type TTL IC, 1С6,.
The clock pulses are generated by a mechanical rotary-encoder which is connected directly to the
shaft of the tuning control knob. The rotary-encoder puts out two signals which are 90 degree out
of phase signals. Clock pulse signals and UP/DOWN signals are generated by the UP/DOWN control
circuit consisting of IC7 and IC8. These signals are fed to Pins 3 and 4 of IC6 through level con-
verters 010 and 011.
SCAN and MIC UP/DOWN CONTROL CIRCUIT
Scan Control Circuit |
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MIC
UP/DOWN
The scan function is provided by pushing the scan Start/Stop (S/S) button. When pushed the S/S
button, Pin 5 of IC6 is lowered to ground level, the voltage at (E) and (Ваге also lowered, and the
multivibrator, consisting of IC7, starts oscillation for scanning, and the decimal point of the
frequency display will blink. When Pin 5 of IC6 is lowered, Pin 3 (UP/DOWN control terminal)
is also lowered, but its voltage is still 1V ~ 2V, so the downward scanning is selected.
The oscillation frequency (scan speed) can be adjusted by R47. When a VFO is selected (in the
programmed scan or full range scan function), the voltage at (G) is ground level, and 09 is turned
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