[evlatests] ea28 L-band Polarizer

[Rob Long]

Hi Rick,

We put this L-band on the bench and discovered that the polarizations 
are actually swapped. We aren't sure how this receiver was missed, but 
it is very clearly cross-pol'd. We are going to verify the OMT, hybrid 
and retest the receiver, but it's also strange that you only saw the 
problem below 1.3 GHz.

It would be interesting to verify that everything is good in ea28 now.

Rob

On 3/15/2022 8:45 AM, Rick Perley wrote:
> Rob, et al.:
>
> Attached is a plot of the cross-polarization.  The narrower plots are 
> the phases, the larger plots are the amplitudes, with y-axis in 
> 'milli-fraction'. RCP above, LCP below.   So, '600' means 60%. You can 
> see the cross polarization reaches 70% at 1.02 GHz.
>
> The 'spiky' polarizations are due to RFI -- I made no attempt to clean 
> this up.
>
> No other antennas look like this.
>
> Rick
>
> On 3/15/22 08:37, Rob Long wrote:
>> 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.
>>>>>>>
>>>>>>> _______________________________________________
>>>>>>> evlatests mailing list
>>>>>>> evlatests at listmgr.nrao.edu
>>>>>>> https://listmgr.nrao.edu/mailman/listinfo/evlatests
>>>>>>
>>>>>> _______________________________________________
>>>>>> evlatests mailing list
>>>>>> evlatests at listmgr.nrao.edu
>>>>>> https://listmgr.nrao.edu/mailman/listinfo/evlatests
>>>>
>>>> _______________________________________________
>>>> evlatests mailing list
>>>> evlatests at listmgr.nrao.edu
>>>> https://listmgr.nrao.edu/mailman/listinfo/evlatests
>>>
>>> _______________________________________________
>>> evlatests mailing list
>>> evlatests at listmgr.nrao.edu
>>> https://listmgr.nrao.edu/mailman/listinfo/evlatests