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

[Walter Shawlee 2]

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
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