TCXO, not OCXO, but related. Sorry, but I have no graphs. I work for a municipal radio shop. We service radios that span 20 years (through acquisitions, it was GE, Ericsson, Com-Net, M/A-COM, Tyco, now Harris). There are several different model handhelds and mobiles, with different designs and TCXO's. Some are adjusted manualy, most via software. I have found that every single TCXO in the various model radios drift downward in frequency over time.
One interesting case was a set of radios that sat on the shelf, unused for several years. They were issued to some custodians about a year ago. I checked all of them on the service monitor beforehand and they were well within spec. All of these radios came back to the shop recently. They were 1-3 KHz low in transmit frequency. That is an unusual amount of drift in one year. Perhaps it has something to do with how long they sat on the shelf. I don't have enough history on our newest radios, so I don't know if this downward trend will hold true for them. Joe Gray W5JG On Sat, Nov 12, 2016 at 2:54 PM, Tom Van Baak <[email protected]> wrote: > There were postings recently about OCXO ageing, or drift rates. > > I've been testing a batch of TBolts for a couple of months and it provides an > interesting set of data from which to make visual answers to recent > questions. Here are three plots. > > > 1) attached plot: TBolt-10day-fit0-e09.gif ( > http://leapsecond.com/pages/tbolt/TBolt-10day-fit0-e09.gif ) > > A bunch of oscillators are measured with a 20-channel system. Each frequency > plot is a free-running TBolt (no GPS, no disciplining). The X-scale is 10 > days and the Y-scale is 1 ppb, or 1e-9 per Y-division. What you see at this > scale is that all the OCXO are quite stable. Also, some of them show drift. > > For example, the OCXO frequency in channel 14 changes by 2e-9 in 10 days for > a drift rate of 2e-10/day. It looks large in this plot but its well under the > typical spec, such as 5e-10/day for a 10811A. We see a variety of drift > rates, including some that appear to be zero: flat line. At this scale, CH13, > for example, seems to have no drift. > > But the drift, when present, appears quite linear. So there are two things to > do. Zoom in and zoom out. > > > 2) attached plot: TBolt-10day-fit0-e10.gif ( > http://leapsecond.com/pages/tbolt/TBolt-10day-fit0-e10.gif ) > > Here we zoom in by changing the Y-scale to 1e-10 per division. The X-scale is > still 10 days. Now we can see the drift much better. Also at this level we > can see instability of each OCXO (or the lab environment). At this scale, > channels CH10 and CH14 are "off the chart". An OCXO like the one in CH01 > climbs by 2e-10 over 10 days for a drift rate of 2e-11/day. This is 25x > better than the 10811A spec. CH13, mentioned above, is not zero drift after > all, but its drift rate is even lower, close to 1e-11/day. > > For some oscillators the wiggles in the data (frequency instability) are > large enough that the drift rate is not clearly measurable. > > The 10-day plots suggests you would not want to try to measure drift rate > based on just one day of data. > > The plots also suggest that drift rate is not a hard constant. Look at any of > the 20 10-day plots. Your eye will tell you that the daily drift rate can > change significantly from day to day to day. > > The plots show that an OCXO doesn't necessarily follow strict rules. In a > sense they each have their own personality. So one needs to be very careful > about algorithms that assume any sort of constant or consistent behavior. > > > 3) attached plot: TBolt-100day-fit0-e08.gif ( > http://leapsecond.com/pages/tbolt/TBolt-100day-fit0-e08.gif ) > > Here we look at 100 days of data instead of just 10 days. To fit, the Y-scale > is now 1e-8 per division. Once a month I created a temporary thermal event in > the lab (the little "speed bumps") which we will ignore for now. > > At this long-term scale, OCXO in CH09 has textbook logarithmic drift. Also > CH14 and CH16. In fact over 100 days most of them are logarithmic but the > coefficients vary considerably so it's hard to see this at a common scale. > Note also the logarithmic curve is vastly more apparent in the first few days > or weeks of operation, but I don't have that data. > > In general, any exponential or log or parabolic or circular curve looks > linear if you're looking close enough. A straight highway may look linear but > the equator is circular. So most OCXO drift (age) with a logarithmic curve > and this is visible over long enough measurements. But for shorter time spans > it will appear linear. Or, more likely, internal and external stability > issues will dominate and this spoils any linear vs. log discussion. > > So is it linear or log? The answer is it depends. Now I sound like Bob ;-) > > /tvb > > _______________________________________________ > 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.
