Technical description
HF SSB Transceiver 9323/9360/9390/9780 Technical Service Manual 4-15
Local oscillators
General
1 04-02972 and 04-03135 Sheet 1
Two digitally controlled synthesised local oscillators are used to drive both the
transmit and receive functions of the first and second mixers. VCO1 operates
between 45.25 MHz and 75 MHz, moving in 2 kHz steps. VCO2 operates in the
range of 44.5435 MHz to 44.5455 MHz, moving in 10 Hz steps.
The synthesisers IC10 and IC13 are programmed in serial data format from the
microprocessor IC101 [104-02976 Sheet 1], which accesses the channel data
stored in the E
2
PROM memory.
Each synthesiser is locked to the reference oscillator. This consists of a
7.304 MHz crystal (Z3) held at a constant temperature by an oven, which is one of
the following:
• a PTC thermistor (E1) at 60°C
• a high stability oven [1 04-03095] where the R3 NTC resistor measures the
temperature of the crystal and causes the op-amp comparator IC1 to vary the
current in the heating element V2 to maintain the temperature of 65°C to within
±1°C
The temperature of the high stability oven is set by R4. V1, R12 and R13 limit the
maximum current through V2 to approximately 400 mA.
VCO1 and phase lock loop (04–02972)
1 04-02972 Sheet 1
The oscillator VCO1 is designed around a differential amplifier consisting of
FETs V8 and V9. The frequency of oscillation is determined by the tuned circuit
L33, C94 and the capacitance of the varicaps D20 to D23. The oscillator output
power is set by source resistors R55 and R58. The resistor R54 assists in
maintaining a constant output level over the operating frequency range.
The oscillator output at the tap of the tuned inductor L33 is coupled via C101 to
an emitter follower V10. The output drives the two mixers IC4 and IC5 and the
prescaler IC9 (all pin 5).
The high frequency output from VCO1 is divided by a 64/65 prescaler IC9, down
to a frequency range of 706 kHz to 1.17 MHz (pins 2 and 3). A high or low on
pin 1 sets the division ratio.
IC10 is a complex chip that contains two programmable dividers and a phase
comparator. The phase comparator compares two input signals of the same
frequency and outputs a voltage that is dependent on their relative phase.
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