[Gb-ccb] some interesting Ka receiver facts from ccb lab tests

[Brian Mason]

In pulling together information for the CCB/GBT calibration I've had a 
more careful look at the lab data with CCB+receiver we collected in 
December. One interesting finding is that feed 1 (particularly left Pol'n) 
has a significantly higher Trx than feed 2, in a way that is consistent 
with the difference being due to something before the first hybrid. It 
does not appear to be consistent with what I would expect the signature of 
longer waveguide in one section to be; I would naively think that would 
show up in *one* output of each feed, not, both of a single feed.

Also one of the radiometers has notably excellent (low) leakage: 1-2% over 
most of the band. In both radiometers the leakage is consistently worse at 
low frequency, which is inconsistent with path length differences being 
the main cause. In the other radiometer the leakage ranges from 5 to 9%.

Summary is at

http://wiki.gb.nrao.edu/bin/view/Projects/CcbDecTrx

(very bottom of the page)

  cheers,
   Brian


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Brian Mason                           | office: +1(304)456-2338
Associate Scientist                   | fax:    +1(304)456-2229
National Radio Astronomy Observatory  | mail:   PO Box 2 
bmason at gb.nrao.edu                    |         Green Bank, WV 24944
http://www.gb.nrao.edu/~bmason/       |
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