Re: VCO drift

[aah@nofs.navy.mil]

Herb Johnson suggested to me an interesting experiment.  He wrote:
>Seems to me that if the VCO was drifting "signifigantly", the
>exposure time would drift and thus the dark current would drift.
  This could be checked by looking at the dark column variability with time.
The main concern I have there is the stability of the TEC.  Dark current
changes roughly a factor of 2 for every 7 degrees temperature change, so
regulating at 0.1C means a 1 percent variation in the dark level is probable.
This is of the same order, or somewhat larger, than the expected VCO drift, and
it might be difficult to separate out the two effects.
  On the other hand, if the astrometric tests indicate a drift, then looking
at the dark columns to see if there is a correlation is certainly a good
check.
  Of course, as Herb also suggested, probably the best way to settle this
whole thread is to just stick a frequency meter on the VCO, especially
at sites where a drift is suspected.
Arne
--------------------------------------------------------------------
Arne Henden                               Instruments/software/CCDs
US Naval Observatory Flagstaff Station    Cepheids/photometry/IR
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