[time-nuts] Wenzel oscillator - L1 value?

[Graeme Zimmer]

Most crystals are cut to be terminated with a certain capacitance.
If you adjust this capacitance you can vary the frequency slightly.

However if you terminate the crystal with a series tuned circuit (L&C) 
you can vary the reactance over a much wider range, and consequently get 
a wider frequency swing.

You simply put an inductor in series with the crystal, with a value 
which resonates with the terminating capacitor at the crystal frequency.
When the tuned circuit is adjusted slightly ether side of resonance, the 
crystal sees either capacitive or inductive reactance. You can adjust 
either the inductor or the capacitor.

With too much variation however, the crystal looses control and the 
circuit becomes free running and unstable.

For back-ground info read up on "Tunable Crystal Oscillators" and 
"Voltage Controlled Crystal Oscillators"

Amateur Radio operators often need to "pull" the frequency of a crystal 
oscillator and have evolved lots of tricks. Look in some of the Amateur 
Handbooks.

One trick is to put two identical crystals in parallel. They behave as 
double-humped over-coupled circuits and can be pulled much further than 
a single crystal.


regards ............ Zim