[evlatests] More on the Big Pulses

[Rick Perley]

     I've looked a bit more closely at the extraordinary RFI.

     1) The period is within 0.1 seconds of 10.0 seconds.  (i.e., I 
count exactly 60 pulses in 600 seconds).

     2) Every few minutes, a pulse is missing.

     3) My earlier estimate of the pulse duration was incorrect. It's 
actually 1 second, or less.  The earlier estimate did not take into 
account the sidelobes of the radiating antenna.  (With a little work, I 
could figure this out -- but I doubt it's worth the effort ...)

     4) The pulse peak power is 10 to 20 times the total power in the 
spectral window -- so ~ 6000 Jy if it came in through the main beam, and 
was distributed uniformly over 128 MHz.  In fact, it's in a single 
channel (so 64X stronger), and likely comes in through a zero dBi 
sidelobe -- so ~ 10^5 stronger than that.  That's a big number.

     4) Attached is a short plot, showing the total power (PSum) in the 
first four IFs, for a short period of time.  It gives a nice lesson on 
the effect of such power over the entire IF.  The two pulses (the 
stronger at 3250 MHz in SPW#3, the weaker at 3206 MHz in SPW#2) are seen 
in the middle two panels.  In the top and bottom panels, the 'pulses' 
are seen as negative -- this is due to compression, presumably in the 
analog electronics, likely the T304.

     5) The pulses are seen with equal strength on all antennas, and 
equally throughout the 1.6 hour duration of the observation.  The former 
rules out a local origin -- the distance of the emitter is many times 
the scale of the array (B-configuration, so of order 100 km or more).   
The latter makes it hard to believe the origin is airborne.  (But I do 
note that the pulse strength varies over a factor ~ 2 over the 1.6 hour 
duration).

     So this sure looks like a radar signal.  Does anybody run a radar 
on top of one of the local mountains, which they were testing this day?  
(May 5th, around noon).
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