[time-nuts] Why do crystals go bad?

gary lists at lazygranch.com
Mon Feb 14 04:15:45 UTC 2011


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 boatanchors at 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
>
>
> _______________________________________________
> time-nuts mailing list -- time-nuts at febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
>




More information about the Time-nuts_lists.febo.com mailing list