Re: ? How to stabilize a cheap colpitts oscillator


"Bruce Varley" <bxvarley@xxxxxxxxxxxxxxx> wrote in message
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"Dave" <db5151@xxxxxxxxxxx> wrote in message
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I replaced the crystal in my basic Colpitts oscillator with a couple
hand-wound toroids and a variable capacitor, and the output now varies
wildly. Any ideas on how to stabilize it a little? Or how to tell if the
problem is my freq counter?

Thanks,

Dave

First, what's 'wildly', and what are you expecting? You'll obviously lose
some frequency stability in changing from a xtal to LC. And is the
amplitude unstable as well, that's a key indicator of what the problem
might be.

Also, IIRC a colpitts osc normally has one inductor. If you're using 2
toroids, is this 2 separate inductors? If so, should it be one inductor
with a tap, providing the mutual coupling that's required?


Wildly: fluctuating from 1.0xxxxx MHz to 6.7xxxx Mhz by degrees of 500 KHz
at a time or more. I was expecting the most significant digit to remain
stable, and the fluctuations to involve the two or three least significant
digits, instead of all digits changing over the span of a couple seconds.
And, no, the amplitude and frequency on the scope are stable, they don't
fluctuate at all. Every now and then it will settle down to roughly what I
expected, but that doesn't last long. No obvious clues as to why.

The two inductors are switched into the circuit one at a time, to allow me
to raise or lower the general frequency range to match that of the circuit I
am trying to test.

Thanks for the reply. Please don't hesitate to offer anything you think
of...

Dave


.

Relevant Pages

  • Re: ? How to stabilize a cheap colpitts oscillator
    ... hand-wound toroids and a variable capacitor, and the output now varies ... Any ideas on how to stabilize it a little? ... IIRC a colpitts osc normally has one inductor. ...
    (sci.electronics.design)
  • Re: Building a bridge ...
    ... some talk in a recent thread about inductors to stabilize the arc. ... I can make and email you pictures of inductor in my Hobart CyberTig, ... your ripple will be as bad ... I recall the neighbor was amazed at how ...
    (sci.engr.joining.welding)
  • Re: Building a bridge ...
    ... some talk in a recent thread about inductors to stabilize the arc. ... I can make and email you pictures of inductor in my Hobart CyberTig, ... your ripple will be as bad ... I recall the neighbor was amazed at how ...
    (sci.engr.joining.welding)