On Tue, 20 Mar 2007 12:08:57 +0000, Ian Jackson
wrote:

You should be able to use the circuit of the single crystal filter
(in-to-out, without the resistive padding etc) as the resonant part in a
VXO, and adjust the neutralization to pull the frequency of oscillation.
It's worth a try.

Ian.
The images primarily showed how the stopband notch moved around.
So I decided to put it into spice.

Compared to L compensation it does seem to have a benefit as higher
frequency peak. It also is not troubled by the side-effect of
L-compensation as passing lower and higher frequencies than those
around the crystal frequency.

Trying to make the most of the balancing compensation I placed a small
capacitor in series with the crystal. This moves the pass band
frequency up a bit more. But the smaller the series cap, the less
pronounced the peak seems to be. Also the circuits starts to attenuate
more and more. This might cause difficulty in an oscillator setup
where the loop gain should stay more than one.

Also with the balanced compensation circuit, the phase is changed
around the peak frequency. Without series cap around -45 degrees,
climbing to -83 with 12pF. This should be accounted for in the
feedback loop of an oscillator. (A properly dimensioned L-compensated
crystal does not change phase.)

But all in all it might be a (complex) method of shifting the working
frequency up.

Joop