[evlatests] A remarkable gain change at P-band

[Rob Long]

Did the T304s reset attenuators between runs? I'm sure they did when you 
went to a calibrator. So much interference in P-band, I wouldn't be 
shocked to see significantly different attenuator settings from run to run.


Rob


On 10/28/2024 1:58 PM, Rick Perley via evlatests wrote:
> I ran a holography test last night (to assist Tracy Clarke in her 
> characterizations of the P-band primary beam).  The SB consisted of 
> four single cuts through the primary beam.  The four cuts were:  
> horizontal, vertical, and two cuts at 45 degree angles.
>
> Each holography cut begins and ends with a short on-source calibrator 
> observation.
>
> A most remarkable thing happened between the first two holography cuts 
> in last night's test:
>
> The amplitude changed, for all antennas.  Some amplitudes went up, 
> others went down.  For some antennas, the change was barely 
> noticeable.  For others, it was as large as a factor of six. (!).  The 
> changes were not the same in the two polarizations.
>
> The effect is due to a gain chang, and not to any antenna or 
> subreflector position error —it is seen in the switched power monitors 
> —both PSum and PDif.
>
> The PSum values, at the beginning of the run, and through to the end 
> of the first holography observation, were normal at near 14 counts.
>
> This gain change occurred only after the first holography scan — about 
> ten to fifteen minutes into the observation.   For all other beam 
> cuts, the gain remained constant (at the wrong power levels).
>
> Any idea what happened?
>
> Rick
>
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