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

[Dan Mertely]

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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