Alfa sky, absorber cal measurement at 1665 Mhz

    100 Mhz filters centered at 1665 Mhz were installed after the dewar on  alfa. The cal values were measured by using absorber and sky as the hot and cold load.  5 second cal on followed by 5 second cal off was repeated 3 times at each position. Since the absorber did not cover the entire array, 4 separate positioning of the absorber were done to cover all of the horns.
    After looking at the data, it was obvious that the cal was not coupling very well into the system. The cal is being  injected before the omt. Instead of computing the cals from the Y factor (since the coupling was so poor) i measured the cals as a ratio of the absorber temperature and sky temperature using the following parameters:
sky temp 5K
rcvTemp 8K
absorber temp 303K
scattered ground radiation 15K
TsysSky=Tsky+Tscattered+Trcv 28K
TsysAbs=Tabs+Trcv 311K

The absorber temperature was measured with a thermometer, the scattered radiation is a value that has been used in other receivers.
The 4 absorber positioning covered the following horns
absorber position #
beams covered

The plots show the results (ps) (pdf)  the measurements. The numbering of the plots has board 1 thru board 7 (which is pixel 0 thru 6).

Some comments:
The cal varies by a large amount across the band.  If the cal is being injected at a null in the wave guide then the variation across the band could come from the changing wavelength. The band covers +/- 3% in lambda (+/- 10deg in phase). If the distance from the injection point to the probes is about a meter then this is 1/.18= 5 lambda's. So we might accumulate 50 degrees of phase across the entire band. Probably not enough to cause the large variation we see in 20 Mhz.

    The probes are not at the same spot so the pattern should be shifted for the two polarizations.

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