[evlatests] ea28 L-band Polarizer

[Rob Long]

Thanks Rick! We thought it was worth a look as a first pass. We will be 
swapping the L-band receiver on maintenance day.

Rob

On 3/15/2022 8:32 AM, Rick Perley via evlatests wrote:
> 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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