Section Vi - Theory Of Operation - Icom IC-230 Instruction Manual

5.4 Transmitting:
| a. Push the РТТ (push to talk) button on the microphone and the transceiver will
transmit: A red transmit indicator lamp comes on below 100 KHz Selector and the
meter will provide an indication of relative power output of the tranmitter. The
neddle will be on or near the eight mark on the meter scale.
b. Hold the microphone about three inches from your mouth and speak in a normal
voice. Shouting does not increase your communication range. The microphone is of
the dynamic type and provides good pickup for all levels of the voice.
c. To receive again, just release the PTT button.
5.5 For Repeater Use:
You may transmit at either 600 KHz above or below the receive frequency for Repeater
use. To decrease the transmit frequency place the "A-B" Switch in the "A" position:
to increase the transmit frequency, place the Switch in the "В" position.
SECTION VI - THEORY OF OPERATION
P.L.L. Synthesizer (Phase Looked Loop)
The P.L.L. consists of four modules: Voltage Controled Oscillator; Phase Detector; Local
Oscillator; and Comparison Oscillator.
6.1 VCO and PD Module
This is a self oscillating circuit with a frequency range of 135. 31 1 to 137.29 MHz, which
is mixed with a 10.7 MHz signal. The result is a frequency of 146.01 to 147.99 MHz.
The frequency of the Hartley oscillator is determined by L1, C9, D1. Dl is a variable
capacitance diode. The capacitance is altered by the voltage at either side. With the time
constant of R6, R8 and C4, when Q3 is cut off, Q2 a unijunction transistor, generates a
sawtooth voltage which is fed to the VCO through R11. The VCO will then sweep from
about 134.5 to 138.5 MHz.
The amplitude of the sweep is controlled by the anode voltage of D1 with potentiiameter
R13.
As an example, if an LO frequency of 124.045 MHz is selected, and the CO frequency is
11.265 MHz, the output of the VCO begins to sweep at about 134.5 MHz. As the
frequency reaches 134.31 MHz, the output from the PD increases and being fed to the
gate of ОЗ causes it to conduct. The voltage dropped by R8 decreases, causing the
increasing voltage. at CP1 to stop, and the frequency of the VCO is held at exactly
135.31 MHz. If the frequency of the VCO increases slightly, because of some change
of the constants in the circuit, the output of the PD becomes negative causing the output
of ОЗ to decrease, the voltage at CP1 increases, and the frequency of the VCO is kept
as accurate as the Crystal controlled LO and CO.
The output of Q2 is fed to the mixing module after pulse components are amplified
by Q1 to be used in indicating "locked" or "unlocked" condition.
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