[evlatests] Noisy C-band antennas?

[Pedro P.B. Beaklini]

Rick, and all,

I did a test last Thursday on this. The thing is that the noise depends 
on the antenna location. The compression is due to an RFI source in the 
direction of stations W36 and N28 and often can be seen in N32, N36, and 
W32 stations. For some reason that we are still investigating, ea17 is 
more affected than others when it is on the RFI path. But the problem 
can be seen in the other antennas in the RFI path.

On the current configuration, there is no antenna on W36 and N28. EA17 
is far away now, at N64, and no compression was seen in my test on ea17, 
in agreement with your data. However, on the antenna closest to W36, 
ea05 at W40, I could see a C-band compression on 3-bit. Please, can you 
take a look at ea05 on your data? I also saw a new noise source leading 
to compression on the east arm ( peak on EA04 at E48). That is new to me 
and needs further investigation, but the effect on data is similar.

If someone wants to take a look at pdif varying in time on my tests and 
past data, I put some shorts movies at. Each frame is 5s, time on top in 
minutes

/lustre/aoc/sciops/pbeaklin/tsys/C-band-issue/2023-06-06/pdif/

As a last comment, I was not the first one to notice the issue. The DAs, 
SRDP team, and the support telescopes group have been aware of that for 
a while. I only decided to take a deeper look at it :-)

Cheers
Pedro

On 6/29/23 14:55, Rick Perley via evlatests wrote:
> Some months ago, Pedro noted that certain antennas were especially 
> noisy (low SNR) for some antennas and spectral windows, when using 
> 3-bit samplers.  From my own data, I confirmed this.
>
> The recent data referred to in my last circular allows a check on this 
> situation -- the data were taken with 3-bit sampler.
>
> The 'noisy' effect is completely gone!  All antennas, in all spectral 
> windows, have exactly the expected sensitivity and gains.
>
> Pedro plans to take some data, to confirm.
>
> Rick
>
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