[evlatests] Strange differential bandpasses

[Drew Medlin]

Here's an observation from a drier time of year. 2021-03-27, afternoon observation, operator recorded Sky cover 40%. Cumuliform clouds.


20A-092.sb39518402.eb39548999.59300.832225300925.ms-J0303+4716-bb12-PHASE-amp_vs_freq-LL_RR.png





Drew Medlin
dmedlin at aoc.nrao.edu

Scientific Data Analyst - VLA Scientific User Support Group
National Radio Astronomy Observatory

> On Aug 27, 2021, at 9:18 AM, rperley <rperley at nrao.edu> wrote:
> 
> Certainly is reasonable.  In the case I analyzed, the start of the run was around sunrise, the end around noon.  The period of the oscillations (and the phase) did not appear to change, however.  The change in amplitude was quite obvious.
> 
> I don't know if there was rain on the day I looked at -- but perhaps dew on the window would do the trick ...
> 
> Rick
> 
> On 2021-08-27 11:11, Ken Sowinski wrote:
>> On Fri, 27 Aug 2021, Rick Perley via evlatests wrote:
>>> Drew, et al.:
>>> Perfect!  Period shown in that C-band plot is about 100 MHz, which corresponds pretty closely to the expected value corresponding to the length of the horn.  Good evidence for a mismatch between the window and the OMT….
>> The change in the sinusoiid should correlate with temperature.
>> Might the reflections have been exacerbated by moisture from
>> all the recent rain?

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