[evlatests] ea28 L-band Polarizer

[Rick Perley]

Removing the RFI monitoring equipment made no difference to the L-band 
polarization problem on ea28.  Observations last evening show the same 
signature -- cross-polarization over 60% at 1.0 GHz, declining to normal 
values (~5%) around 1400 MHz, and staying near that level up to 2 GHz.

Rick

On 3/14/22 16:00, Dan Dillon via evlatests wrote:
> We have made a change and removed the RFI monitoring equipment from 
> the L-band to help isolate the problem.  Can we repeat the testing to 
> see if this made any difference before we just replace the receiver?
>
> On 3/13/2022 9:07 AM, Wes Grammer wrote:
>> That definitely sounds like a receiver issue, either with the OMT or 
>> (more likely) the quad hybrid coupler that immediately follows it. 
>> This L-band should come back to the lab for evaluation and repair.
>>
>> On 3/12/2022 12:40 PM, Frank Schinzel via evlatests wrote:
>>> I second this observation. I have been seeing this behavior of ea28 
>>> at L-band in 5 independent observations since February 26.
>>>
>>> On 3/12/2022 12:19 PM, Rick Perley via evlatests wrote:
>>>> Something is seriously amiss with the L-band polarizer in ea28.
>>>>
>>>> Normal cross-polarizations are typically 5%, and never more than 
>>>> 10%.  For ea28, these values are seen above 1300 MHz, but below 
>>>> this, the cross-polarization rises quickly to more than 50% at 1050 
>>>> MHz.
>>>>
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