[evlatests] New (?) X-band RFI

[rperley]

Mert, et al.:

I'm thinking it's more likely a GSO.  The duration of the RFI -- about 
10 minutes, translates to about 2.5 degrees in antenna motion -- about 
right for getting the Ku-band beam far enough away.  An LEO goes much, 
much faster, so I'd expect the duration to be a lot shorter.

Also to note that the RFI was not seen at all on the flux calibrator 
(about 20 degrees away).  This is not proof against an LEO, but does 
support a GSO origin.

Rick

On 2021-01-26 15:14, Mert wrote:
> Well Rick, if it was truly rapidly moving, it does sound more like a 
> LEO
> than a GSO satellite.  That would increase the possibility that you
> managed to get a first VLA confirmed detection of a SpaceX StarLink LEO
> satellite (which just so happened to be conveniently camouflaged at 
> that
> moment in front of the Clark belt).  -Mert
> 
> 
>> Dan, et al.:
>> Looking at more data, it's clear the RFI is from a rapidly moving
> object.  The duration of the RFI is only 10 minutes or so, after which,
> all appears close to normal.
>> Another thing I noted:  The same RFI is seen at a higher frequency --
> 11.46 to 11.82 GHz.  It's clear that these signals are also broadband,
> and 'blocked' in frequency in a similar manner to that reported 
> earlier,
> between 10.95 and 11.19 GHz.  The time correlation is exact -- all of
> these rise and fall in precisely the same way.  They must have the same
> origin.
>> Curiously, the frequency span from 11.19 to 11.46 is completely clean. 
>> Rick
>> On 2021-01-26 11:19, Mert wrote:
>>> Hi Rick.  There is a passive-only band between 10.680 and 10.700 GHz, 
>>> but
>>> 10.7-12.7 GHz is all fixed microwave (terrestrial point-to-point) and
> space-to-earth satellite transmissions.  We (RA) do have some footnoted
> protections there, but only to the extent that their transmissions
> might
>>> affect the 10.680 and 10.700 GHz band.  Those are the "hooks" that 
>>> Harvey
>>> Liszt has been using to try to prevent RFI from the new SpaceX 
>>> StarLink
> broadband internet service from being too disruptive to RA.
>>> I know that there are some fixed microwave systems in the area in the 
>>> "11
>>> GHz band", but I'd have to check on the exact frequencies.  Otherwise 
>>> I'd
>>> say that you are seeing standard GSO satellite transponders.  
>>> (StarLink is
>>> non-GSO, so we could only be sure of a StarLink detection if we see 
>>> the
> source away from Dec 0.  GSO downlinks have been in the 10.7-12.7 GHz
> band, like, forever.  30-40 MHz bandwidth per transponder channel
> sounds
>>> likely.)  -Mert
>>>> In a recent run, some strong RFI, seen only short spacings only (due 
>>>> to
>>> fringe-winding and A config) was seen between:
>>>> 10.950 and 11.190 GHz.
>>>> The spectral characteristics show these to be in 6 spectral 
>>>> 'chunks',
>>> each 40 MHz wide.
>>>> The RFI was not seen on the (northern) calibrator, but was obvious 
>>>> on
>>> the target source, located at Dec = -5.5  So, likely a geostationary
> satellite.
>>>> @Dan:  Any idea what's responsible?
>>>> Rick
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