[evlatests] Wobbles hard to find!

[Rick Perley]

    Ken and I tried to find wobbles today, using WIDAR and the VLA 
correlator -- almost entirely without success.  (However, we did find 
the S-band RFI signals, reported earlier ...)

    The idea was to dump data as fast as possible (apparently, this is 
now 250 msec -- not fast enough to efficiently find lots of wobbles, but 
sufficient to (usually) find a few ...), at L, S, C, and X bands, with 
WIDAR.  Then we switched to the VLA correlator, and dumped data at its 
fastest rate, 418 msec. 

    For the most part, we saw no clearly identifiable wobbles at any 
band, with either correlator.  However, we did find:

    1) That S-band, with the VLA correlator, shows large slow 
oscillations in amp and phase in IF#2 only.  This was a mystery until I 
got to the WIDAR data -- it turns out that I chose a frequency in IF2 
which overlaps 3200 MHz -- so the oscillations are due to the 
newly-found RFI reported earlier.  (This also means that the 128-MHz 
separated RFI lines are not due to WIDAR itself). 

    2) We did find amplitude wobbles on baseline 8 x 27, in IF2 in RCP 
only at all four bands -- all with the same period of 1.5 seconds.  No 
such periodicity or variability was seen in the WIDAR data from the same 
frequency and polarization on that baseline.  

    There was marginal evidence that baseline 19 x 25 showed 'wobbles' 
of the 'standard' variety. 

    We do not understand why the data taken on the same source (3C345) 
two days ago, at about the same time, showed such strong wobbles, while 
today they are absent ...