[evlatests] An Extraordinary RFI signal at S-band

[Rick Perley]

     I have been calibrating 13 short (1.5 -- 2 hour) Sband observing 
runs, all taken during May.  Twelve of these are as expected (= very 
good!).  One is not ...

     The run taken on 05 May, starting near 11 AM shows extraordinary 
interference, at a frequency that I've not seen RFI in before.  The 
characteristics are:

     1) Period = 10 seconds (exactly), with each pulse being ~ 2 seconds 
long.
     2) VERY strong -- up to 40 dB above the noise level (!)
     3) Both polarizations (not surprising, given it's likely to come 
through the sidelobes).
     4) There were two frequencies:  3250 MHz, and 3206 MHz.  The first 
was very much stronger than the other, but the two are definitely 
linked.  (I imagine the weaker one could have been a non-linear 
responseof the stronger -- but no other is seen in the 3.0 -- 4.0 GHz 
band).
     5) The RFI was seen throughout the 1.6 hour duration.

  All spectral windows had their PSum and PDif values strongly 
affected.  With some effort, I can edit these, and since the emission 
was completely 'off' for ~ 80% of the time, I may yet get decent data.

     Does anybody have an idea where this mystery signal came from? Has 
it ever been seen before (not by me).

     Rick