[evlatests] A most interesting RFI event

[Walter Brisken]

Hi Rick,

With fairly high certainty, the event on Mar 13 was GPS satellite PRN 
27  (SCN 38833).  I calculate its coordinates as:

Date      Time (UTC) RA           Dec         Range (m)    Az      El
2021MAR13 18h33m00s  5h40m35.67s  50d01'00.4" 2.37510e+04  41.0596 17.8700

I suspect the one you see the next day is also a GPS satellite.

I calculated a while back that within the 10 MHz transmission band a GPS 
satellite is approximately 12 MJy.

 	-Walter

-------------------------
Walter Brisken
NRAO
Deputy Assistant Director for VLBA Development
(505)-234-5912 (cell)
(575)-835-7133 (office; not useful during COVID times)

On Thu, 8 Apr 2021, rperley via evlatests wrote:

> The long (16 hour) L-band holography run, done March 13/14, contains two 
> extraordinary events which appear to be due to satellite borne radiation. 
> The characteristics are unusual ...
>
> 1) Only the RCP channels were affected.  LCP shows nearly no effect.
> 2) Both events took about 1 minute, with smooth changes throughout, and 
> maximum effect exactly in the middle.
> 3) The correlated power, monitored total power, and the synchronous power 
> were all affected.  The (digital) total power was 'beam-like' -- plotted 
> versus time, we see nice sidelobes, and the inner main beam, superposed on a 
> large negative offset.
> 4) Only the reference antennas were affected!  There were six of these, and 
> all showed the effects about equally.  None of the target antennas saw 
> anything at all.  These were 10 to 15 beamwidths away at the time (or, 5 to 7 
> degrees) of the events.
> 5) The perturbations were much stronger in the lower frequency SPW (1445 MHz) 
> than the high frequency one (1820 MHz), and the first event was much stronger 
> than the later one.
> 6) The effects were no uniform in frequency -- the upper frequency part of 
> the lower window (1381 -- 1509 MHz) was much more strongly affected.
>
> From this, I deduce:
>
> 1) An RCP-emitting signal passed through the main beam, at an angular rate of 
> about 1 degree/minute.
> 2) The signal is strong enough to depress the gains of the entire front end.
> 3) The true signal frequency is likely in the 1500 -- 1600 MHz range.
>
> For reference, here are the times and the pointing directions at the time of 
> the incidents.  Perhaps somebody can figure out what hit us:
>
> #1 event:  13 March 2021 at 18:33 IAT.  Az = 41, El = 17.
>
> #2 event:  14 March 2021 at 05:30 IAT.  Az = 309, El = 46.
>
> Rick
>
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