[evlatests] No Wobbles at S-Band!!!

[Rick Perley]

    The origin of the 'wobbles' seen yesterday is now understood. 

    It is due to an RFI spike (actually, an internal 'birdie') at 2944 
MHz, strong enough to beat with the continuum emission of 3C147, and 
visible only on the north-arm baselines because of the (relatively) slow 
fringe rate at the time. 

    A bit of numerology:  2944 = 23 * 128.  This is the 23rd harmonic of 
a 128 MHz fundamental tone.  The problem is well known -- indeed, 
perusal of the spectrum shows a harmonic in *every* S-band subband 
(conveniently, each is 128 MHz wide, so it's easy to find).  The odd 
multiples are stronger, as expected. 

    Not only is the origin of this problem known, but so is its 
solution.  We have been waiting for a long time to survey the spectrum 
for other such internal birdies, but it seems that this 'RFI Sweep' 
survey is still some time away.   Perhaps it's time to get on with 
eliminating this known problem?