[time-nuts] HP 5061Cs reference question

[paul swed]

Yes indeed I used the GPSDO to do exactly that.
When I play with the synthesizer things go all over the place.
As someone pointed out a long time ago, the synthesizer doesn't behave as
you may think. Logically I had believed that a LSD of 1 change would be
some simple shift. But it seems that was wrong.
What I am looking at may be a drift thats far smaller the 1 LSD. I can't
really tell.
Regards

On Sat, Dec 6, 2014 at 11:22 AM, Magnus Danielson <
magnus at rubidium.dyndns.org> wrote:

> Paul,
>
> On 12/06/2014 04:51 PM, paul swed wrote:
>
>> Magnus
>> Great but I am looking for very specific detail. If you pick a wrong peak
>> especially if you can't see peaks on a very weak tube then I think that
>> translates into an actual offset.
>>
>
> Yes, there will be a significant offset unless you adjust your synthesizer
> frequency accordingly, which few clocks allow you to do.
>
> Then, if you have a weak tube, then the center pidestal is the most likely
> to lock onto.
>
>  If thats a true statement. Given the modern GPS boxes we have today that
>> are stable. Wouldn't you see that as a always constant drift. Say 7-10ns
>> over 20 minutes?
>>
>
> It would be significant yes, and it depends on the C-field, but in
> general, the C-field is so strong as it separates of the -3, -2, -1, +1, +2
> and +3 peaks from the central 0 peak so that it can be observed without
> interference. The C-field will offset the 0 peak un a much lower degree
> than it offsets the closer -1 and +1 peaks (which is also weaker). The
> nominal C-field setting is reflected in the synthesizer offset and balances
> out. That way most cesiums isn't really as "primary" as being advertized.
>
>  If you restart the system it magically comes back to the same offset.
>> Also there is a second harmonic reading and control. If you very the fine
>> phase on the 5 MHz indeed the ctl voltage readout adjusts and the system
>> is
>> locked. Green light.
>>
>
> It is actually the strength of the 1st harmonic which is interesting,
> since if you have strong 2nd degree with almost zero 1st degree, then you
> are pretty much on the mark (i.e. lock).
>
>  Here is the real issue the tube has always been so weak that you simply
>> can't look at the i meter and see humps. What I had done a long time ago
>> was add in another meter that was very sensitive and then use a magnifying
>> glass to see the peaks.
>>
>
> I wired up a network analyzer with a mixer to re-modulate the response
> onto the 12.6 MHz signal. Worked like a charm, but slow scanning rate is
> recommended. I think I did some photos of that.
>
> Anyway, on a weak tube, you are most likely to lock to the 0 pedistal,
> because it is the strongest of all 7. If you have a GPSDO you can pre-tune
> your OCXO to help locking.
>
> Cheers,
> Magnus
>
>
>
>> Regards
>> Paul
>> WB8TSL
>>
>> On Sat, Dec 6, 2014 at 10:41 AM, Magnus Danielson <
>> magnus at rubidium.dyndns.org> wrote:
>>
>>  Hi Paul and Bob
>>>
>>> On 12/06/2014 04:04 PM, Bob Camp wrote:
>>>
>>>  Hi
>>>>
>>>> Sure you can set them on the wrong peak. If you really get confused, you
>>>> can also set them on the wrong transition … (gulp).
>>>>
>>>> Peak wise, the one you want is the highest Q / best SNR. Set it to one
>>>> of
>>>> the others and your ADEV degrades.
>>>>
>>>> Transition wise … not a good idea at all.
>>>>
>>>>
>>> It's worse than that. Of the 7 peaks, the middle one has significantly
>>> least sensitivity to the C-field, as well as having the strongest
>>> response.
>>>
>>> The "new" digital cesiums actually measures the near-by peaks to sense
>>> the
>>> C-field and servo the C-field and then use the center peak for servo the
>>> frequency. This is a key to increase the stability of frequency and
>>> reduce
>>> a systematic effect.
>>>
>>> Cheers,
>>> Magnus
>>>
>>>
>>>   Bob
>>>
>>>>
>>>>   On Dec 6, 2014, at 9:11 AM, paul swed <paulswedb at gmail.com> wrote:
>>>>
>>>>>
>>>>> I have a curious question that really applies to all Cs references.
>>>>> Its possible to set them on to the wrong peak.
>>>>> Typically in the literature it will speak to at least 3 peaks and you
>>>>> want
>>>>> to select the highest central peak.
>>>>> However if you select the wrong peak, how much would the output
>>>>> frequency
>>>>> be off?
>>>>> I had read a tech note for the airforce that seems to indicate its
>>>>> pretty
>>>>> easy to get on to the wrong peak.
>>>>> Regards
>>>>> Paul
>>>>> WB8TSL
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