Hi again Mike I fully agree with your direction of effort into the aerial
improvements. Your signal strength has increased a lot since I started
listening.
On the crystal mixer front, I lashed up a source from crystal modules out of
an old Pye Westminster (the fundamental oscillators, usually the TX pcbs) I
found that by taking the fixed padding (2 by 18pF) off and leaving the 12pF
trimmer, I could connect a differential capacitor across the crystal-trimmer
caps swinging one up and the other went down. That way I could cover the
whole band with a pair of carefully chosen rocks. The result seemed quite
stable but I have not given it exhaustive tests. These units are channel
switched by grounding the emitter line so can be keyed directly. The
resultant waveform with just one oscillator keyed doesn't look too bad.
The most probable problem could be that the differential cap is a single
bearing job (A bit of good old Govt surplus) and liable to vibrate
mechanically. It might be possible to do the same thing with varactors and a
twin gang pot, except that the tuning law would perhaps be a bit odd.
73 de Alan G3NYK
|
