The VFO is a simple Clapp/Gouriet oscillator. J113 FET's are used for the VFO and first buffer amp. One pole of a double pole, six way switch is used for band switching. The other pole is used to supply DC to the BPF and LPF boards. The digital display and stabiliser unit controls the frequency by feeding a DC control voltage to a varicap diode in the VFO.
The capacitor marked '*' is a 'gimmick' capacitor, made from two short lengths of insulated wire twisted together. The value of this capacitor is chosen to give a frequency change of 2KHz over the control voltage range of 1V to 4V. The 47pF and 220PF capacitors should be polystyrene, silvered mica, or NPO ceramic types. I used a good quality air spaced tuning capacitor with a 60:1 anti-backlash reduction drive.
The inductor (L) is wound on a ceramic former.
The coil in this VFO has 44 turns. Once again, I have stolen ideas from other
projects on this site.
