[time-nuts] HP 10811 stabilizing time

[Richard (Rick) Karlquist]

The military contracts were very important for the counter product line.
I suspect that the EFC feature was required in order to bid.  The
way things worked at HP, special features for the military were
basically walled off from the civilian market.  The project manager
for the 5335A worked in marketing for a while so he should have
been aware of any customer demand for this feature.

It is also well to realize that back in those days, nobody had
GPS based standards.  The counter would be sent to a cal shop
to be calibrated periodically.  The resolution of the coarse
adjustment was adequate compared to the amount of aging that
occurred between calibrations, so an EFC board would be
superfluous.  Customers who had an atomic standard or a
LORAN receiver like ourselves distributed it as a house
standard and didn't even install 10811's in counters.  So
an EFC was like a solution in search of a problem.

Rick

On 7/23/2019 4:01 AM, Charles Steinmetz wrote:
> Rick wrote:
> 
>> Basically, no counter that we ever made AFAIK had
>> any provision for EFC.
> 
> The later HP5328 "oscillator helper" boards have EFC pots for fine 
> tuning the timebase frequency.  This includes the US military versions 
> that are so prevalent in the US.  I have schematics showing this with 
> both the 10544 (support board 05328-60027) and 10811 (support board 
> 05328-60038) oscillators (production shifted from the 10544 to the 10811 
> during the 5328's run).
> 
> These work fine, but one can easily build an EFC circuit with much 
> better drift characteristics (i.e., first-order temperature 
> compensation).  I published such a circuit some time ago and posted it 
> to this list at least once.  My circuit also reduces the EFC adjustment 
> range to make it easier to adjust precisely.
> 
> That circuit is on Didier's site (ko4bb.com).  Search for a doc named 
> "HP 10544 10811 EFC fine adjustment.pdf".
> 
> Best regards,
> 
> Charles
> 
> 
> 
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