Two authors come to mind regarding crystal oscillators: Eric Vittoz and
Marvin Ferking. Eric Vittoz is the more modern of the two. His writings
tend towards long term stability of crystal oscillators. Basically, most
designs put too much energy into the crystal, which he claims wears it
out. I'd had to dig up his papers, but my recollection is the failures
were soft (error in frequency) rather than hard (total failure). Ferking
covers temperature stability and crystal pulling.
I haven't dealt with crystal manufacturers in a long time, but my
recollection is the crystal is "tuned" by metal deposition. As you
deposit metal on the crystal, the frequency lowers. Possibly today they
laser trim, i.e. remove metal. Anyway, I don't think opening up the case
and fiddling with the innards is a good idea.
In the dark ages, when I took a class in wafer fabrication, we would
sense the amount of metal sputtered on the wafer by measuring the
frequency shift of a crystal in the chamber. As you sputtered metal, the
crystal frequency would get lower.
Ferking's DSP book is supposedly the bible in software defined radios.
Back to crystal manufacturers, these companies tend to be pretty small.
when I was working on video chip designs, it was no problem talking to
the CEO or VP engineering. I think it is a capital intensive rather than
labor intensive business. They have a few gurus doing product design and
that's about it.
In the dark ages, these guys were the easiest to deal with for technical
info:
http://www.crovencrystals.com/
They have an impressive list of projects that they worked on:
http://www.crovencrystals.com/croven_pdf/heritageprograms.pdf
On 2/13/2011 7:26 PM, Bill Hawkins wrote:
Group,
Jim Garland on the boatanch...@theporch.com list asked about crystals:
"A 22.5MHz crystal (HC-5 case) in my homebrew receiver, built about forty
years ago, no longer oscillates. It seems to be purely an age-related
problem.
It is in a standard solid state circuit which bandswitches six crystals, and
the other five work just fine. I wonder what causes a crystal to stop
working, and whether it is possible to repair them? I've "repaired" dead
100kHz calibrator crystals, and hamband crystals in FT-243 cases, by
cleaning off the brass pressure plates, but am not sure if one can do this
on thin high crystals. As I recall, the metal electrodes are evaporated onto
the sides of the element. 73, Jim W8ZR"
One of the replies was:
"Broken families, drugs, drink... the normal, I suppose. John K5MO"
Scott Robinson asked: "Receiver crystals aren't getting beaten up by high
power,
but something has killed a lot of them in my R-390A and Drake R-4A.
Curiously yours, Scott"
And Roy Morgan asked:
"I have a 1960's frequency standard from a Nike site: the Sulzer Oscillator
and would like to find tech into on it."
Any help appreciated.
Bill Hawkins
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