[evlatests] A most interesting RFI event

[Dan Mertely]

Hi Rick.  I looked carefully at the W8mon plot for 20210313, 18:33 IAT 
(11:33 MST) (attached, annotated) and do not see any significant RFI 
events around that time.  Note that the time scale is compressed by 
about 1 hour in 24, but at midday the time axis should be within 1/2 
hour of correct.  Nothing shows near the end of the daily plot either, 
whereas you detected a notable event at "14 March 2021 at 05:30 IAT" 
(22:30 MST).

I do see a short, wide-band event at around 09:00 MST (16:00 UTC), but 
no significant detections near the 2 times you recorded.


As a comparison, I've also included the 24 hour plot for the prior day, 
20210312, in which you can see some notable GPS hits at the time 
indicated as 13:50 MST, and especially 16:30 MST.  No such significant 
GPS hits can be seen on the 24 hour plot for 20210313 however.

For those on the list who are not familiar with the W8mon L-band 
monitor, it is a analog, hardware tap off of the RCP output channel of 
the L-band cryogenic receiver on (currently) ea28 on pad W8.  Since we 
have excess gain over the spectrum analyzer's noise floor, the 
background noise level seen on the plots corresponds closely to the 
instantaneous noise temp of the cryogenic receiver (around 35 K).

I don't know what could be the cause of the RFI you noticed on the 13th, 
the W8mon did not see any unusual activity at those times.
-Mert


On 4/8/2021 10:35 AM, 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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