I'm pleased to hear that you have made use of the idea. My original
objective was to be able to readily adjust the frequency of a calibration
grade oscillator, for which fractional ppm is adequate. Your 0.5 Hz at 137
kHz is 3.6 ppm.
Since my earlier report I received a request to check the slope of the delta
emitter gradient, so that it could be used under automatic control in a
phased locked loop. I checked a different design Colpitts crystal
oscillator to "double check" on gradient matters. I confirmed that the
technique worked for fine tuning each, but the slope was "opposite". So if
a particular oscillator is to be used in a PLL application, it needs to be
characterised for delta slope before designing the VCO drive.
Someone reading these postings may have a suggestion as to the semiconductor
mechanism(s) that bring about a variation in oscillator frequency. It would
be unfortunate if some oscillator design had an S curve for frequency versus
73, Bob ZL2CA
----- Original Message -----
From: "Lawrence Mayhead" <[email protected]>
To: <[email protected]>
Sent: Thursday, June 10, 2004 12:56 AM
Subject: LF: re Xtal osc "delta emitter" tuning
Thanks Bob for the sugestion, I have been looking for a means to pull the
oscillator that I use for QRS and DFCW.
The cap. in series with the xtal gives me coarse adjustment and now the
emitter resistance change enables a "fine tune".
I am able to achieve 0.5hz shift in the final 137 khz output. although I
need to reduce the emitter resistance by 50% to