[evlatests] Modcomp-Free Tests, 18 May

[Jim Ulvestad]

Antennas 3 and 7 (see bottom of Rick's truncated message below)
are the most distant VLA antennas on the E and N arms. 
However, 22 is the most distant VLA antenna on the W arm,
and doesn't seem to show this effect at W72?

Jim

Rick Perley wrote:
>     I ran my standard 'torture test' of the system Friday afternoon.    
> I've carefully reviewed the L-Band data from this, and the top-level 
> summary is that, once a few rather gross problems are identified and 
> removed, the situation doesn't look hopeless at all!  Indeed, there may 
> be reason for optimism ...
>
>     Read on for some details. 
>
>     The test was in two blocks:
>
>     A)  23 minutes in 'Modcomp-ON' mode, observing first in continuum 
> (std. 50 Mhz, 0.418 sec averaging), each band from L through Q, then in 
> spectral line (mode 4, 12.5 MHz BW, 3.3 second avg). 
>
>     The Modcomp-free system was then installed (takes about 5 minutes)
>
>     B) The same 23-minute file as above. 
>
>     Major results (from L-Band only):
>
>     I filled the data with all flags turned off, so I could see 
> everything, no matter how bad.  I haven't yet filled with the flags on 
> -- that effort may have to be delayed a bit, due to time pressures from 
> other activities. 
>     At first review, the Modcomp-free data looked just dreadful.  But it 
> was fairly quickly found that once two major issues were identified and 
> removed, data quality looked pretty good:
>
>     1) Antennas 3 and 7 appeared to be near-dead on all IFs, all 
> baselines, both in line and continuum -- so the problem is not a delay.  
> In review the baseline-spectra, it was quickly seen that the phases are 
> oscillating back and forth by 180 degrees on alternative channels.  
> (This will very neatly kill the coherent signal!) 
>