[time-nuts] Antique Rubidium Standard Questions

[Ed Palmer]

Paul,

On 4/24/2012 5:24 PM, paul swed wrote:
> When all else fails check the grounds. Especially 40 year old screws.

Been there, done that.  This unit had multiple problems with bad 
soldered ground connections.  I went through the unit and resoldered 
everything that looked the least bit odd.  I didn't find any screws that 
were electrically significant.  Maybe I should look again!

Ed

> On Tue, Apr 24, 2012 at 6:13 PM, ed breya<eb at telight.com>  wrote:
>
>> Ed,
>>
>> Tuning the cavity should peak everything - it just maximizes the
>> excitation power at the microwave frequency, so you get the most output
>> from the Rb light wavelengths. A mechanical cavity resonator will have a
>> very wide (compared to the modulation frequencies you're looking for)
>> bandwidth, so unless something happened to it physically, it should be OK
>> as originally built or adjusted. However, you may want to look at the
>> multiplier chain and SRD bias circuit components and adjustments - those
>> could have drifted quite a bit over forty years, limiting the microwave
>> power due to being off-frequency, or having poor multiplication efficiency.
>>
>> I'm guessing that the second harmonic is indeed present, but just buried
>> in the noise, and the loop still can "lock" because of the further signal
>> processing, even though you don't see the evidence - remember it's a
>> lock-in amplifier capable of digging a tiny signal out of the noise. If you
>> go through the multiplier and check and tweak things, you may get more
>> excitation power and signs that it's getting back to normal. Once you get
>> enough power, if the Rb cells are still good, the second harmonic signal
>> should show up large enough for the circuit to detect sufficient S/N ratio
>> and provide a valid lock indication.
>>
>> Ed Breya
>>
>>
>> Ed Palmer wrote:
>>
>> Could the drift be at least partially responsible for the lack of second
>> harmonic?  A message on the list (
>> <http://www.febo.com/**pipermail/time-nuts/2006-**April/020562.html<http://www.febo.com/pipermail/time-nuts/2006-April/020562.html>
>>> http://www.**febo.com/pipermail/time-nuts/**2006-April/020562.html<http://www.febo.com/pipermail/time-nuts/2006-April/020562.html>) said
>> that you could peak the second harmonic by adjusting the cavity tuning.
>> If the cell and the cavity are out of sync would that kill the second
>> harmonic?  How close to they have to be?  If this thing has a cavity
>> tuning adjustment I haven't found it.
>>
>>
>>
>>
>>
>>
>>
>>
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