[time-nuts] Adjusting HP 5065A frequency

John Ackermann N8UR jra at febo.com
Sun Oct 21 11:58:45 EDT 2012


Hi Edgardo --

One slightly frustrating thing about the 5065A is that its frequency settability isn't as good as its short term stability.  I believe the manual says that the small divisions on the C-field counter dial are 2x10e12, and it's hard to set closer than that.

A good 5065A is a remarkable piece of gear, with medium term stability over, say, 1K to 100K seconds that is very hard to beat by anything other than a maser.  As best I can measure mine against a number of other sources (no maser here, sigh), it is around 1e13, maybe a bit better, over that range.  That's an order of magnitude better than any of the telco Rbs.

This is just a guess, but from some data that tvb and others have reported, I suspect that external tempco is the main limiter for medium term stability in the 5065A.  It would be interesting to see one in a temperature-controlled environment vs. one that's not.

John

On Oct 21, 2012, at 11:11 AM, Edgardo Molina <xe1xus at amsat.org> wrote:

> Dear Corby,
> 
> Good morning. Thank you for the detailed instructions to bring the 5065A close to desired frequency. I couldn't have a cleaner explanation of the process. 
> 
> Yesterday evening I tried adjusting the C field in small steps using a mixer, lpf and two oscillators setup as my current frequency counter is not able to resolve de small increments/decrements of frequency adjustment. Still I could detect the adjustments as I performed them. The response is quite fast. I have been told that these units are really stable compared to the small telecom Rb units. I heard a comment that the 5065A is even more stable than the new Symmetricom units using the X72 Rb module. Have you ever measured such differences in stability?
> 
> Thank you.
> 
> Regards,
> 
> 
> 
> 
> Edgardo Molina
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> On Oct 19, 2012, at 5:55 PM, cdelect at juno.com wrote:
> 
>> Edgardo,
>> 
>> You do use the C-field adjust to put a 5065A "On frequency". The Factory
>> values are a moot point after all these years!
>> 
>> Just incrementaly adjust the c-field control in small steps while
>> observing the frequency comparison. 
>> 
>> The only thing that might happen is that you reach one end of the C-field
>> pot before getting to the frequency you want.
>> 
>> If that is the case you will need to set the synthesizer switch to the
>> next value in the chart. (either up or down depending on which way you
>> ran out of room.)
>> 
>> Then start over with the c=field adjustment.
>> 
>> If you switch the synthesizer setting you will need to remove power
>> momentarily to reset the synthesizers lock indication circuit. Otherwise
>> pushing the logic reset button to get the green light wont work.
>> 
>> Corby
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