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

[Dan Mertely]

OK, it sounds like all of the data were taken
before our latest attempt at mitigation.  It
will be interesting to see if the ripple is
less noticeable now.  -Mert

On 10/4/2019 3:04 PM, Rick Perley via evlatests wrote:
> 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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