[mmaimcal] Re: [alma-sw-ssr] question about frequency/band switching speeds and rates

[Ed Fomalont]

Hi Bryan,

    I've finally looked at your rates and speeds for the ALMA
hardware.

1.  Frequency switching seems reasonable.  How many warm bands will
there be?  Three?  So, if you want to cycle over more than 3 bands, it
will take alot of time.  So, the observing schedule would have to
be made efficient.

2.  Correlator reconfiguation limits seems okay, but see OTF next.

3.  My calculations for OTF give an integration time M, as a function
of frequency and OTF rate as

   M = 150 msec / FREQ(THz) / RATE(sidereal).
This assumes a saltation every 1/3 FWHP.

For FREQ = 0.8, RATE=6 (maximum suggested)
   M = 30 msec    Too short with current design

For FREQ = 0.3, RATE=1 (drift scans)
   M = 500 msec

So, correlator 48 msec update cycle (I'm checking on this) is probably
okay except for the fastest OTF at the highest frequency.

4.  Nodding rate: The maximum nodding rate that may be used will, in
fact, depend on the nodding speed (including settling time).  You
probably don't want to spend more than 1/3 of the time not observing a
cal or target.  If the WVR system works well, nodding may be minutes
rather than seconds may be enough

5.  Subarray redefinition: I can't image this occurring very
frequently.  I don't see why anyone would want to do redefine
subarrays more often than every few minutes, if even that.

Ed