The PTC crystal heater may be one of the reasons for your sucess in pulling
it so far. Most crystals are designed for nominal 20 deg operation, and if
you heat them up the frequency drops. These crystal heaters are
particularly useful for /P microwave operators as they allow < 1ppm from a
cheap and simple oven. But the crystal must be cut for operation at 50 deg
or whatever temperature is chosen.
Many of us initially tried the 40 deg heaters on normal 20 deg crystals and
found worse stability than not using any heater when exposed to the wide
variations out in the field. What happened is that the rise in operating
temperature moved the location on the freq / temp response away from the
point of inflexion, where it is not too sensitive to a few degrees of
variation, (it has a cubic law) onto a steeper part of the curve so the
whole arrangement was now a lot more sensitive to external temperature
effects.
However, using one of these heaters indoors, where temperature is already
quite constant does not show the effect so much and does give improved
stability over a few degrees variation.
Andy G4JNT
-----Original Message-----
From: John Andrews [mailto:[email protected]]
Sent: 2001-08-01 12:40
To: [email protected]
Subject: LF: Re: SV: Re: SV: LF Receivers
Johan,
>Do you have any circuit suggestion for a suitable "rock bender"?
I just used a simple Pierce FET oscillator, followed by an
LM6321 buffer,
and it worked. I have an air variable trimmer for rough setting, and a
tuning diode run by a 10 turn pot. I did glue a PTC thermistor to the
crystal to help with temperature. I'll know more about
stability in a couple
of weeks.
John Andrews, W1TAG
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