[evlatests] New (?) X-band RFI

[Harvey Liszt]

10 minutes is an eternity in the 90-minute orbit of a LEO satellite.

SpaceX and OneWeb are both channelized in 250 MHz blocks from 10.95 up 
.  The press says that SpaceX is not serving latitudes as far south as 
the VLA yet and OneWeb isn't operating at all as far as I understand.

Stay safe

regards

Harvey

On 1/26/21 3:34 PM, rperley wrote:
> 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
>>>>> _______________________________________________
>>>>> evlatests mailing list
>>>>> evlatests at listmgr.nrao.edu
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-- 
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Harvey S. Liszt
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