[evlatests] ea28 L-band Polarizer -- All Better!

[Rick Perley]

I looked through the 'historical' records -- this antenna had normal 
polarization in January 2020.  I've not found any more recent data yet ...

Rick

On 3/17/22 15:04, Rob Long wrote:
> Thanks Rick,
>
> We're looking closely at the L-band in the lab.
>
> Rob
>
> On 3/17/2022 2:58 PM, Rick Perley wrote:
>> Attached is the new plot (amplitudes only) for ea28 at Lband, from 
>> observations taken earlier this morning.
>>
>> It's now completely normal.  Note that the scale runs from 0 to 10% 
>> (the former plot tan from 0 to 60%).
>>
>> I have no idea how or why it's better -- but it is ...
>>
>> Rick
>>
>> On 3/17/22 11:49, Rob Long wrote:
>>> Hi Rick,
>>>
>>> The OMT on the L-band receiver from ea28 was definitely built 
>>> backwards. Wes, Dan and I discussed this and we are a bit confused 
>>> as to how this could have gone undetected for so long (or your 
>>> current test results). Lets definitely check ea28 again and verify 
>>> that everything looks normal now.
>>>
>>> Anyway, fyi.
>>> Rob
>>>
>>> On 3/17/2022 10:02 AM, Rick Perley wrote:
>>>>  Rob:
>>>>
>>>> This is hard to understand -- the polarizations are right 'in the 
>>>> end' -- so there must have been a 'counter-swap' elsewhere. If one 
>>>> antenna has reversed polarization, and the others do not, the 
>>>> result is very easy to see in the data. This is not seen.
>>>>
>>>> And this certainly won't explain why the cross-polarization is so 
>>>> bad at the low frequency end, but ok at the high frequency end...
>>>>
>>>> Rick
>>>>
>>>> On 3/17/22 09:41, Rob Long wrote:
>>>>> 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