[mmaimcal] forwarded message from Stephane Guilloteau

[Steven T. Myers]

In discussions on subarrays with Larry, I proposed that subarrays be
divided into two types:

  "Hard" subarrays - a group of antennas that require a single
                     independently tunable first LO

  "Soft" subarrays - a group of antennas that share a first LO tuning
                     with another subarray, but which may use different
                     2nd LO settings (which run off a fixed reference)
                     or other system controls (eg. correlator settings).

I would agree that a sufficient number of Hard subarrays would be 4, as
many of the cases I presented in previous mails could be dealt with
as Soft subarrays (in conjunction with a simultaneous Hard subarray).
This is Case #1 that Stephane proposes.  Note we would routinely be
operating with 2-3 Hard subarrays (eg. VLBI,Main Interf,Sec Interf for
second line band or transient studies) so having an extra available would
likely meet our projected needs.

I am not sure if we need to distinguish between the correlator control
and the rest of the system (Stephane's Cases 2 and 3) as different Soft
subarray modes.  Could we set both of these specs to 8 to simplify?
Or is there a good reason to have Case 2 be only 6, such as complications
regarding Phase Switching and/or correlator binning (for sideband
separation with DSB mixers)?  I would marginally prefer to set the
Soft subarray limit (correlator and system) to a uniform maximum of 8.

I see no problem with the proposed limits, namely the critical Hard
subarray (Case 1) limit of a maximum of 4 simultaneous independently 
tunable first LO signals.

   -Steve

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|:| Steven T. Myers                      |:|  Associate Scientist      |:|
|:| National Radio Astronomy Observatory |:|                           |:|
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|:| smyers at nrao.edu                      |:|  FAX: (505) 835-7027      |:|
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On Fri, 24 Mar 2000, Al Wootten wrote:

> Comments?
>