[evlatests] Bandpass Ripple in ea28, RCP, L-band

[Rick Perley]

The C configuration data were taken 15 Dec, 2018.

The B configuration data were taken 18 Apr, 2019

The A configuration data were taken 16 Aug, 2019

Rick

On 10/4/19 3:01 PM, Dan Mertely via evlatests wrote:
> Hi Rick. Could you tell me the dates of the observations?
> We worked on the W8mon back on 4 September, but haven't
> heard whether our connector cleaning fixed the problem.
> -Mert
>
> On 10/4/2019 10:28 AM, Rick Perley via evlatests wrote:
>>      I'd like to return to this topic, with some more information.
>>
>>      There is no doubt that the W8 RFI monitor is the guilty party.  
>> The new information is this:
>>
>>      The data came in three configurations:  For the first, ea24 was 
>> on W8.  For the second and third, ea28 was on W8.  In reviewing the 
>> calibration, I find:F
>>
>>      a)The rapid oscillation noted before is on these antennas -- and 
>> only these antennas.
>>
>>      b) The cross-polarization signals (RL and LR correlations) are 
>> *completely ruined* on all baselines connected to ea24 for the first 
>> configuration, and ea28 for the other two.
>>
>>      The reason for this cross-polarization problem is that the 
>> fine-scale ripple is both extremely large, and extremely time 
>> variable. So there is no way we can realistically 'calibrate it 
>> out'.      No doubt the parallel-hand signal (for the polarization 
>> used for that monitor) is similarly affected by the time variability.
>>
>>      The fact that this problem was easily visible on two different 
>> antennas (which occupied the same pad -- W8), on three observations 
>> spanning many months, strongly suggests that many other observations 
>> have been affected.
>>
>>      Hence my questions:
>>
>>      A) Has the current problem (with ea28) been repaired?
>>
>>      B) Do we really need this monitor?  Unless the reflection 
>> associated with this monitor is reduced by at least 20dB, the 
>> observational data cannot be used.
>>
>>
>> On 9/3/19 2:42 PM, jjackson via evlatests wrote:
>>> Wes and I just had a chat about this and our chief suspect would be 
>>> the W8 RFI monitor cable that is connected to L-band on this 
>>> antenna. The length is just too long for anything else to make sense 
>>> on a single polarization.  30 meters would be about right for the 
>>> length of the cable running down the antenna.  We'll have someone 
>>> take a look at it.
>>>
>>> Jim
>>>
>>>
>>>
>>>
>>>
>>> On 9/3/2019 11:01 AM, Rick Perley via evlatests wrote:
>>>>      Bandpass solutions from my Cygnus A observations, taken in 
>>>> April and August this year show a strong bandpass ripple in RCP 
>>>> only, for antenna 28 and L-band.  The period of the ripple is about 
>>>> 4.6 MHz, corresponding to 30 meters if the cause is a reflection. 
>>>> The problem was not visible in data taken in December last year.
>>>>
>>>>      The ripple pattern is strongly time dependent (both in its 
>>>> amplitude and phase), so is very difficult to calibrate out.
>>>>
>>>>
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