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<[email protected]> 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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