[time-nuts] hp 10544A and 10811A ovenized oscillators

[Bob kb8tq]

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 <walter2 at 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)
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