Addendum
Page 2, 12-50093 Issue 1 HF SSB Transceiver X2 Technical Service Manual
Local Oscillators
Introduction
Each synthesizer 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 where the R3 NTC (Negative Temperature Coefficient)
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
o
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.
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