[daip] Possible problem with FRING

[Eric Greisen]

Lincoln Greenhill writes:
 > > 
 > > Glad to hear it.  One more thing, I forgot to mention this
 > > before but I notice you are using DOCAL=1, for VLBA data
 > > you should probably be using DOCAL=2 which calibrates the
 > > weights.  DOCAL=1 did this before March 2000.
 > 
 > Hi Amy,
 > I am back on line.  I am not aware that DOCAL=1 ever calibrated weights. 
 > via the gains in a CL table.  Did I misunderstand (now or then)?
 > 
 > We do not have a mixed array of antennas so the use of DOCAL=1 for FRING
 > is probably not too bad.  Do tests show otherwise?
 > 

          FRING used to calibrate weights without any user control - a
wrong thing for the old VLA style of weights, but seldom wrong for
VLBA data.  Even if the array is "uniform", some telescopes' receivers
will work better than others.  In the VLBA the elevations will vary
between telescopes so the amount of spillover/ground pickup will vary.
I would have made it DOCALIB=2 to NOT cal weights if I thought the
users would have put up with that much change but chickened out.
In the VLA, receivers vary in noise by factors of 2 even between
polarizations or IFs on the same telescope.

Eric