[mmaimcal] Receiver Specs Needed!

[Steven T. Myers]

    RECEIVER SPECS NEEDED FROM IMCAL GROUP

    Version 27 March 2000

    S.T. MYERS (NRAO, Socorro)

    These are a list of issues discussed at the JRDG meeting
    held in Charlottesville 20-21 March 2000 that need input from
    the Imaging and Calibration group.  I graciously "volunteered"
    the help of Larray and the ImCal group in setting these specs.

    We should start from Larry's latest version of rcvrSpecs.txt:

            http://www.tuc.nrao.edu/~ldaddari/rcvrSpecs.txt

    which has been updated 2000-Mar-16 for the JRDG meeting.  The
    most critical things needed are those marked "TBD" in Larry's
    document.  I have therefore taken the following items from
    his memo.

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List of Receiver and Optics Specs Required
Deadline: 3 April 2000

   o What are the implications of the 1% cal spec, as regards
     to the performance of the WVR (should it be cooled?) and
     the need for a cold load?

   o What are the scientific and calibration requirements of the
     polarization performance, both interferometrically and
     in total-power (single-dish) mode?  (Larry asks for maximum
     cross-polarization and polarization mismatch between antennas.)

   o What are the scientific and calibration stability requirements
     for the gain fluctuations in total power modes for each band?
     (The current spec is 1E-4 at 1Hz, but we should have some specs
     over a wider frequency range as per Larry's request.)

   o What are the specific specs for Band 1, which may have to have
     non-optimum optics (eg. mirror size, off-axis placement) and
     poorer total-power stability? (We should have some fallback 
     relaxed specs in this band.)

It would also be a good idea to revisit and firm up the specs on:

   o What are the limits for minimum image sideband rejection (in dB)
     for the expected worst-case continuum and more critically narrow
     band signals in the image sideband?  (The feeling is that 10dB 
     is enough in hybrid schemes and some QO schemes claim on 7dB.)

   o What are the limits on optical aberrations (I and polarization)
     that are tolerable from the scientific and calibration
     standpoints?

   o What are the implications of adopting DSB front-ends and thus
     performing the sideband separation or rejection in the back-end
     and correlator? (The phase switching will require some minimum
     time to cycle through the Walsh functions and thus we may have
     to limit the number of antennas in the subarray doing this when
     fast switching or scanning is desired.)

   o Are there any unacceptable tuning limitations of Larry's LO
     scheme (as modeled by Barry's handy C program)? (I am not sure
     that anyone has actually done this fully.)

Anything else?

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|:| Steven T. Myers                      |:|  Associate Scientist      |:|
|:| National Radio Astronomy Observatory |:|                           |:|
|:| P.O. Box O                           |:|  1003 Lopezville Rd.      |:|
|:| Socorro, NM 87801                    |:|  Ph:  (505) 835-7294      |:|
|:| smyers at nrao.edu                      |:|  FAX: (505) 835-7027      |:|
|:| http://www.aoc.nrao.edu/~smyers      |:|                           |:|
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