[time-nuts] Antique Rubidium Standard Questions

[Ed Palmer]

Paul,

Good suggestion, but I don't think pop rivets had been invented when 
they built this thing! :-D   It's built like a piece of mil-spec 
equipment.  When I google for individual parts, I keep tripping over NSN 
numbers.  Now that I look closely at it, I realize that the case is just 
the case with no electrical connection between it and the circuit other 
than the BNC jacks on the front panel.  The concept of 'chassis ground' 
is an unknown concept.  I don't think there's even one chassis ground 
lug anywhere.  Even when I'm poking around inside the unit, there are no 
live wires that I can touch, everything is insulated.  The build quality 
is very high.

But now that you've got me thinking about it, I think there's something 
weird about the grounding in the physics package.  I've got to take 
another look at that.

Thanks!

Ed


On 4/25/2012 8:59 PM, paul swed wrote:
> Ed look for pop rivetted ground logs. Famous for going bad. HP even used
> them.
> Drill em out and put real bolts and lock washers in
>
> On Tue, Apr 24, 2012 at 7:34 PM, Ed Palmer<ed_palmer at sasktel.net>  wrote:
>
>> 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>)
>>>> 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.