[mmaimcal] Draft initial response to B7 sideband gain relaxation request

[Stéphane Guilloteau]

Hi everybody

         Here are my first reactions

- The gain in sensitivity is clear in approving this CRE
- The Single-Dish sideband separation remains the only critical issue. The 
options are

1) select a subset of 4 dedicated cartridges with better sideband rejection 
for the 4 Single-Dish antennas.
    This may be cumbersome, but could cerainly work at the level expected 
from the original specification.
2) Apply a clever sideband retrieval scheme, involving sideband gain ratio 
measurement made from the
    interferometric mode. Because of different scales at signal and image 
frequencies, this has not yet been
    demonstrated in all cases.
3) Apply the sideband smearing scheme, by LO scanning during 
observations.  The drawback is that
    it suppresses the (spectroscopic) image sideband. Hence, in the Band 7 
scheme, where only 4 GHz
    per sideband is available, this scheme requires twice more time to 
acquire the full 8 GHz (per polarization),
    by smearing alternatively the upper and the lower sideband.

Using the last option as the main observing mode,  I argue that the gain in 
sensitivity offered by relaxing the sideband rejection to allow better SSB 
system temperature largely offsets the extra time required to acquire 
separately the two sidebands in the Single Dish mode, specially as only 25 
% of the projects required Single-Dish mode (see the DRSP).

         Regards and good luck

                 Stephane



A 14:25 23/04/2007 -0400, Al Wootten a écrit :
>Folks
>
>Let's discuss this at 3pm in the small conference room in the NAASC, those 
>of us in CV.  If others with to join, please let me know and I'll turn on 
>the phone.  There is an IPT leads telecon tomorrow morning to discuss this 
>topic at about 1130 am EDT.
>
>I an eager to hear your reactions.  We have been instructed to approve 
>this CRE by the PM but I think we should quantify the toll this will take 
>on project science.
>
>Clear skies,
>Al
>
>
>
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Dr. Stephane GUILLOTEAU
L3AB, Observatoire de Bordeaux
2 rue de l'Observatoire
         F-33270 FLOIRAC,  France

Tel: (33) 557 77 61 68
Mobile (33) 683 84 66 70
E-Mail: guilloteau at obs.u-bordeaux1.fr