[evlatests] EVLA & Satellite interference

[Rick Perley]

    Thanks to Vivek for doing this. 

    We do need to start thinking more seriously on these issues.  The 
talk given this week by Gerry Harp explained another characteristic that 
Bob and I had seen in our wideband S-band tips -- at elevations below 
about 30 degrees, the spectra between about 3800 and 4200 MHz were 
filled with a kind of 'trash'.  We were pointed towards the east.  It 
now seems all this is from TV downlinks from geostationary satellites.  
The effects of these signals were not huge -- at worst, Tsys (i.e. the 
total power) at some frequencies was about doubled -- we have no worries 
about saturation (unless we hit one dead-on).  But there are likely to 
be large az/el areas where astronomical observing at some frequencies 
cannot be usefully done. 
    We need to start 'mapping' out these forbidden zones, and learning 
more about just how deep we can go within them. 

   

Vivek Dhawan wrote:
> For a satellite of known orbit, VLA az/el is easy to get - e.g. I can
> confirm that Rick's S-band measurements, reported last week, hit one of
> the 3 Sirius satellites which wander all over the sky. There are also 4
> XM birds perched at fixed locations.
>
> More generally, the orbits (when public) are available at an excellent
> site run by T.S. Kelso:      http://celestrak.com/
> About 1200 active satellites are listed, my guess is about a third are
> potential sources- e.g. there are 380 geostationary satellites, 140 of
> which are over the horizon at the VLA.
>
> Frequencies of satellites are known to varying degrees, I do not know if
> someone has a reliable list out there, or if NRAO is up to date on this.
> I bet almost every transmitter is between 1-50 GHz.
>
> I am open to suggestions as to what we can or should do, and who should
> spend time on it. I am prepared to generate orbits for specific requests,
> (which take some minutes to set up and automate for future updates),
> but not too much more.
>
> No surprize here - this is one of those despoiled commons that everyone
> decries but no one, including me, wants to spend time on.
>
> Vivek.
>
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