I periodically check that. On Nov 12, 2016 5:43 PM, "Adrian Godwin" <[email protected]> wrote:
> What if your shop reference were drifting up ? > > > On Sat, Nov 12, 2016 at 11:25 PM, Joseph Gray <[email protected]> wrote: > > > 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. > > > _______________________________________________ > 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.
