You've got that high frequency cavity oscillator, that runs from 256 to
512MHz, which is successively divided down for the lower bands. When I was
working at Rockwell-Collins, those 8640s had a sticker on them, stating that
the unit needed to be on for at least 72 hours, before making any
measurements. They do take awhile to stabilize.

Pete

Paul Erickson wrote in message
...
I have an Hp-8640b opt 323 that seems to be working fine,
except the final two digits of the frequency display keep
fluctuating, even after 3 hours of warmup. Is this normal
or how do I go about fixing this?

cheers, Paul - VA7NT email