And sorry about the typos! Still getting used to this touch screen! Sent from my iPhone
On Feb 14, 2011, at 19:47, Shawn Tayler <[email protected]> wrote: > Very interesting Bob Thanks. > > It brings to mind an annoying issue I run into from time to time. > > VCXO 12.8 Mhz used as a reference in communications gear. Most of the gear > is roughly 10 years old and of similar make, both mobile and portable styles. > They all are dropping in operating frequency. Many as far as 3000 hz at 850 > MHz but it does vary with most in the 1300 hz area. The trim adjustment is > made through a programming interface and in some cases we are running out of > adjustment. > > My question is what is the process in the aging if the crystals that causes > this drop in frequency? I understand it may be mechanical but the level if > vibration the radios are exposed to varies greatly and there does not seem to > be a correlation with the frequency shift we are seeing. > > Just thought I start a discussion. I thinks still soy of on topic? > > Shawn > > Sent from my iPhone > > On Feb 14, 2011, at 5:02, Bob Camp <[email protected]> wrote: > >> Hi >> >>> From a number of radios I've torn crystals out of and looked at: >> >> 1) The blank is broken / cracked. Most likely the radio got dropped >> somewhere along the line. Just like that stone hit on your windshield (on >> two cars at the moment), the crack can start small and propagate. Time from >> impact to failure might be years. >> >> 2) Cement fractures. Except in pressure mounts, the blank is held in the >> holder (clips) with cement. Normally this both holds the part and makes >> electrical connection. Some epoxies shrink with time eventually they shrink >> enough to crack. Big enough crack at the wrong place = no electrical contact. >> >> 3) Plating adhesion. Metal is deposited on the blank using a thin film >> process. If everything is nice and clean, and it's the right metal it sticks >> very nicely. If it's the wrong metal or stuff is dirty - not so much. Add to >> that (possibly high) drive and the metal comes off. Loose enough metal and >> it stops working. >> >> 4) Air in the package. On high performance / low frequency crystals (think 5 >> MHz 3rd), the parts run in vacuum. Let in air and the resistance goes up a >> lot. High resistance = no works. >> >> 5) Broken mounts. If you put enough vibration on a crystal for long enough, >> at the right frequency, you break the mounts. Often this is right where the >> mount hits the post coming up from the base. Happens mostly in mobile gear. >> You can do it with random vibe, but much easier to do with a sine at the >> right frequency. >> >> 6) Contamination. Put a fine layer of crud on the surface of a crystal and >> you can stop it dead. It acts as a mechanical damper, especially at low >> drive levels (like startup). >> >> --------------- >> >> Stuff that you see in papers: >> >> 7) Micro fractures. The machining process that makes the blank bashes away >> at the blank on a microscopic level. Stone to windshield on a micro scale. >> >> That's no where near a complete list, but it's a start. I have seen no >> convincing evidence of a wear out mechanism in a quartz resonator. Quartz is >> pretty sturdy stuff. There are lots of examples of parts older than I am >> still out there running. They do age on and on, they don't seem to die >> except when they are deliberately killed. >> >> Bob >> >> On Feb 13, 2011, at 10:26 PM, Bill Hawkins wrote: >> >>> Group, >>> >>> Jim Garland on the [email protected] 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 -- [email protected] >>> To unsubscribe, go to >>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >>> and follow the instructions there. >> >> >> _______________________________________________ >> time-nuts mailing list -- [email protected] >> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
