[evlatests] Sirius Satellite 'Danger Zones'

[Rick Perley]

     Recent observations of northern sources at S-band have highlighted 
the danger of the Sirius satellite system.

     There are three satellites, each in an elliptical, 24-hour orbit, 
cleverly arranged to each spends about 9 hours more-or-less hovering 
above the central US.   As one departs (to the SW), another arrives from 
the SE to take its place.

     From the VLA, the area where the satellites spend the great 
majority of the time is between azimuth 0 and +50 degrees, and 
elevations 55 to 75 degrees.    Thus, roughly speaking, sources with 
declination between 50 and 70 degrees, and at hour angles of -2.5 to 0, 
can expect to be near one of these satellites.

     The effect can be quite dramatic:

     1) The affects are almost entirely seen in LCP.  (Note:  The Sirius 
website claims the satellite broadcasts in RCP, so either they, or we, 
have their definitions reversed ...).

     2)  No perceptible effect is seen if the satellite is more than 30 
degrees away.

     3) If the satellite is 20 -- 30 degrees away, a few percent loss of 
gain (due to compression of the signal chain, presumably the last analog 
device, or perhaps the sampler) is seen, in LCP only in all SPWs.

     4) If the satellite is within 10 degrees of the target, total 
compression of the LCP chain will occur (near zero power in both PSum 
and PDif), in all SPWs.

     5) Perhaps needless to say, SPW03 (which covers the frequencies the 
satellite broadcasts on) is completely saturated when the satellite is 
within 30 degrees.

     If Vivek and I can find a little time, we'll generate a memo with 
better displays of the effects.

     Rick