Hi The change is suspiciously close to the electrical tuning range of a typical HP OCXO. The answer may be a failure of the bias on the EFC line …..
Bob > On Nov 2, 2018, at 2:51 PM, Walter Shawlee 2 <walt...@sphere.bc.ca> wrote: > > I have several of these as the -010 high stability timebase options > in my various HP counters, and generally they work very well, with > usual errors under 0.01Hz and very minor drift over time. > > a few months ago, I had a power interruption, and black out for a few hours, > along with the usual erratic restart from the power company. shortly > afterwards, I built a nice little > homemade TM500 plug-in OCXO unit to fit on my bench, and without giving it > much thought, used > my bench standard (an hp 435B-K26 power/frequency reference with an internal > 10544A) to cal it. all seemed good. > > soon after, I was working on an hp 5334A counter, and added a 10811A as as > upgrade from my > spares and suddenly, I had a big 1.3Hz error at 10Mhz when I cross checked it > to my bench references AND a rubidium. I brought over my recently cal'd > rubidium from the upstairs lab, and yes, there was now clearly a big step > error. my upstairs 5335A with a 10811A had the same step effect! > > these 2 units are always on for stability, so both got cycled the same way > during the power failure. > > it seems that the power failure cycle had bumped the internal 10544A > oscillator inside the 435 by that amount, as well as the 10811A inside the > 5335A. I have never seen that effect before, both the ovenized osicllators > from hp have been very reliable for me, so I thought I would put that info > out in case anyone else has seen this effect and knows the cause. > > using the rubidium (which I keep off until I need it, and wait for at least 2 > hours for best settling), I reset everything back to a flat 10Mhz, and all > was well, except that the first 10811A I put in the 5334A conked out (oven > still fine, but the oscillator went dead, giving the dreaded "no osc" message > on the counter). another spare fixed that, and two days of drift testing to > get everything back where it belongs. anybody want the bad 10811A? > > anyway, just thought the information might be handy for others. the EFC > range on the 10811A/10544A is *only 1Hz*, so such a big jump is unusual to > say the least. it required the main coarse adjustment to fix. > The 435B-K26 is a pretty remarkable widget if you ever see one, it makes a > great 10Mhz reference and 1mW power reference in one little box, very useful > for an RF bench. One of hp's rare and forgotten treasures. > > all the best, > walter > > -- > Walter Shawlee 2 > Sphere Research Corp. 3394 Sunnyside Rd. > West Kelowna, BC, V1Z 2V4 CANADA > Phone: +1 (250-769-1834 -:- http://www.sphere.bc.ca > We're all in one boat, no matter how it looks to you. (WS2) > All you need is love. (John Lennon) > But, that doesn't mean other things don't come in handy. (WS2) > > _______________________________________________ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
