[evlatests] Wideband X-band test results

[Michael Rupen]

>    We ran a short (50 minute) test of the basic 'wideband' mode at
> X-band:
>
>    * One IF (AC)
>    * 8 subbands of 128 MHz each
>    * full polarization
>    * center frequency 8.400 GHz (so the frequency spanned is 7.888
> through 8.912 GHz)
>    * maximum 3 minutes duration for each observation.
>
>    The sources were 3C286, Cygnus A, and its nearby calibrator,
> J2007+4029.  I followed Michael's prescription in setting up the OPT
> script:  start with four successive 'OSRO' observations, and limit
> durations to 3 minutes maximum.  Referenced pointing was not utilized.
>
>    The data are of absolutely, astonishingly, good quality!
>
>    A quick perusal of the data (it is a holiday, after all) reveals:
>
>    1) Only 0.43% integer zero visibilities.
>    2) 27 antennas fringed successfully on both IFs
>    3) *NO* 'failures to tune' -- all antennas and both polarizations
> fringed every time.
>    4) The only flagging required was for antenna slewing.
>    5) No phase jumps.
>    6) No amplitude jumps.
>
>    Data quality from all antennas is simply superb.  I haven't seen
> anything like this for many months.   CALIB reports a mean closure error
> of 0.043% which sounds rather good...


This should be a very easy run -- one setup, no tuning changes, etc.
I'd be interested to hear about phase and amplitude stability, esp.
IF/pol'n differences, which in my last X-band (OSRO) test showed
lots of jumps (5%-ish).

>    But there is one annoying issue, which is no surprise:  The subbands
> are mislabeled -- they are both 'out of order', and have their frequency
> axis reversed.  I corrected the latter problem using 'TABPUT'.  What is
> now needed is to interchange subbands 1 with 8, 2 with 7, 3 with 6, and
> 4 with 5.  I don't know if AIPS can do this without actually copying out
> each subband separately, and gluing them back together in the right order.

Just to be certain -- the frequency axis for each subband (IF in AIPS)
is *wrong*, or just not what you expected?

       Michael