Hi Modern OCXO’s are set up based on temperature run data. They play with set point (and possibly electrical gain) to optimize the TC contribution of the crystal *and* the rest of the parts in the device. This is true of single and double ovens.
One not so obvious point is that these runs are done in a very specific temperature environment. Forced air is normally part of a test chamber. It also is often part of the OEM installation that the OCXO goes into. Change the “air pattern” to much and you change the gain of the oven ( more insulation increases the gain). This can upset the careful balance done when optimizing the TC of the device. One can debate just how stable all of the “stuff” in an OCXO is over the years. Is a set ( or screening ) done on a production line a decade ago still relevant today? Random bits of evidence suggest that the TC optimization holds pretty well, but there isn’t a lot of data. A typical double oven should be < 5x10^-10 over 0 to 70C. Indeed many manufacturers will sell you examples that are spec’d tighter than that. Some offer single ovens with spec’s below 1 ppb over 0 to 70. 1x10^-8 is a very typical single oven spec. How well does this or that example do? It is not uncommon to see 1x10^-8 level single ovens rolling off the production line at <2x10^-9. On some designs > 80% of the units do this. Counting on any and every OCXO to be 5X better than spec …. maybe not, but many designs do. How to “manage” an OCXO? First step it to get a good one in the first place. If eBay is your source of supply ( it is for me ….) what you get likely is not going to be 100% perfect. Some level of testing and sorting will be involved. That needs to be done before a lot of additional effort is put in. Next up is to plan on keeping it on power all the time. OCXO’s don’t like to be cycled. Sorry about that. If this bugs you, don’t head down this road. There are good reasons for this to bug you so do think about it. Drafts and abrupt temperature changes are to be avoided. Opening the lab window next to your reference standard … not a great idea. Something as simple as a towel or a cardboard box tossed over the device can do wonders. Exotic enclosures are probably better, but simple gets you a long way. Thermal mass might help as well. Just as a note, things like Rb standards (and Masers) also are said to benefit from fairly simple “draft protection” enclosures. Most folks are pretty obsessive about regulated supplies. If anything they go a bit overboard in terms of noise for an OCXO supply. What might get overlooked is the need for a fairly substantial ( = low voltage drop) supply wiring setup (along with good ground practices). If you plan some sort of battery backup, consider the regulation impact as it cuts in and out. Loading on the output of an OCXO does matter. How much is a “design feature”. It is not uncommon to see a few minutes of disruption for a significant load change. Simple answer here is not to play with moving things around a lot :) Many OCXO’s are tuned via an EFC. Feeding this input in a stable fashion can get a bit crazy. Do try to run the EFC circuit ground straight back to the OCXO. Oven current induced drops are not great for EFC stability …. Fun !!! Bob > On Jul 1, 2022, at 6:40 AM, Erik Kaashoek via time-nuts > <time-nuts@lists.febo.com> wrote: > > I'm trying to build a stable reference for a phase noise meter project and > have acquired a double oven XO that boosts high short term stability (below > 1e-12/s). But the spec also states that, even with the double oven, there is > still substantial impact of environmental temperature changes (below 1e-8 > changes over the normal operating temperature range) so I was wandering if > its good practice to try to thermally isolate the DOCXO or do you run the > risk of overheating as it always may burn some power and its better to only > shield it from draft? > _______________________________________________ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe send an email to time-nuts-le...@lists.febo.com _______________________________________________ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com