When all else fails check the grounds. Especially 40 year old screws. 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. > > > > > > > > > ______________________________**_________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/** > mailman/listinfo/time-nuts<https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts> > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
