[daip] How should I interpret this?

[Jim Ulvestad]

Johan van der Walt wrote:
> 
> I have started the editing and calibration of the data of a run we had
> on the VLA in June.
> 
> I have followed the procedure in section 4.3.1 (initial editing) and
> noted that for a specific calibrator the values are round about 800 -
> 900 for about the first 40 seconds on the source. For the remaining 80
> seconds on the source the values given by LISTR are between 80 and 90,
> ie 10 times smaller than during the first 40 seconds. This applies to
> all baselines. It also seems to occur only for one specific calibrator
> source but not for everytime when it was observed.
> 
> Is this bad data?
> 
> Johan

The most obvious possibility is that the data are fine, but the scale
in your LISTR changed by a factor of 10.  When LISTR prints things out,
it
gives an amplitude scaling factor at the top of each header--my guess is
that you had some baseline that got above 1000, so LISTR re-scaled
things
down by a factor of 10.

Another thing you can do to check this is do a LISTR with OPTYP='MATX'
for the entire affected scan, and select the option to plot amp+rms,
i.e., DPARM(1)=3.  If you really had a problem with the data, you would
get a huge rms.  If the rms is small relative to the amplitude, then
there's probably nothing wrong with your data.

Jim Ulvestad