In message <[email protected]>, Charles Steinmetz w rites:
>Warren pointed out that the MV89 has a double oven and said that this >makes added thermal capacitance unnecessary. It's more complex than that. A regular singleoven OCXO usually has a pretty high heating current so it can regulate both up and down and therefore handle rather brutal changes in ambient temperature/air-flow etc. Double oven OCXOs, in particular "high-end" models, are usually much better thermally insulated and therefore draw a lot less heating current. That is not a problem when they are exposed to sudden cooling, they can regulate heating up as fast as they need. But when they are exposed to sudden heating, they cannot regulate the heating current negative. I have seen this assymetry with a number of double oven OCXOs. The best way to mitigate it, is to make sure the temperature does not rise rapidly. Unfortunately, that is almost the most common failure case: A/C or local fans failing. Wrapping the OCXO in thermal insulation is an option, but not a good one, since it will drive the heating current even further down. Good idea for battery power though. What you want is to wrap your OCXO in a thermal impedance. The best result I have managed so far, was by wrapping the OCXO in domesticated geology, (bricks, concrete, cinderblocks etc), which has high-ish thermal capacity but only moderate thermal conductance. But for some reason people stare incredously at you, if you request 4U rackspace for a cinderblock. -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 [email protected] | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence. _______________________________________________ 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.
