AIPS HELP file for FXALIAS in 31DEC21
As of Sun May 16 18:44:02 2021
FXALIAS: process data set to remove EVLA-EVLA aliasing issue
INNAME Input UV file name (name)
INCLASS Input UV file name (class)
INSEQ 0.0 9999.0 Input UV file name (seq. #)
INDISK 0.0 9.0 Input UV file disk unit #
SOURCES Source names for line sources
NO '-' usage
CALSOUR Continuum source names
NCOUNT 1.0 30.0 Use 1st NCOUNT CALSOUR for BP
TIMERANG Time range to use
FLAGVER -1.0 Flag table version
BDROP 1.0 512.0 start chan in cal for cont
EDROP 1.0 512.0 end chan in cal for cont
OUTNAME Output UV file name (name)
OUTCLASS Output UV file name (class)
OUTSEQ -1.0 9999.0 Output UV file name (seq. #)
OUTDISK 0.0 9.0 Output UV file disk unit #.
BCHAN Lowest channel for cals
ECHAN Highest channel for cals
ICHANSEL Select channels to fit: NOTE
this is start,end,increment
and IF for each region
DPARM -1.0 1.0 <=0 => average polarizations,
IFs, times, antennas
(5) > 0 keep imaginary
(6) > Hanning smooth
Procedure: EXPERIMENTAL PROCEDURE
This procedure does a special spectral fit designed to correct
for aliasing of the continuum into the observing band found
only for EVLA-EVLA baselines when observed in the VLA-EVLA
transition with the old correlator.
The process which one must undertake to correct data affected
by this problem is:
1. Flag EVLA-EVLA baselines in the FG table
2. Run BPASS on the VLA-VLA and VLA-EVLA baselines writing out
amplitude-only bandpass functions
3. Undo the EVLA-EVLA baseline flagging in the FG table
4. Run SPLAT to apply the BP table
5. Run UVCOP on one or more calibrator scans to make a data set
for the alias "cal"
6. Run FIXAL applying the cals of step 5. It reads in the data
averaging each baseline.pol/IF separately. Sums up the cal
channels BDROP through EDROP and divides the cal by this
complex average. Then it fits the normalized cal to the
channels of the input data to get the continuum flux and
subtracts the channel-dependent part of that from the data.
This procedure has been written to help implement this
process. Note that it does these operations in the simplest
way. If you want BPASS (step 2) run in special ways, SPLAT run
with, for example, DOBAND > 1, etc. you may have to run the
steps yourself. The DPARM parameter allows you to experiment
with different aliasing functions. By default all baselines,
polarizations, IFs, and times are averaged together and the
imaginary part of the aliasing function is zeroed. You can
remove some or all of this averaging and can select Hanning
smoothing of the aliasing function for improved S/N.
If you have a data set consisting of only EVLA-EVLA baselines
from a frequency unavailable to VKA antennas, things are more
difficult. You will need a data set at a nearby frequency that
includes the VLA antennas. Run FXALIAS on this data set. Take
the FXALIAS.UVCOP data set and run FIXAL on the bandpass cals
of your main data. Specify only channels which are not
affected too badly by the bandpass and by the alias. Then run
BPASS on these cals. Apply the bandpass to the main data with
SPLAT. Then run FIXAL on the SPLAT output with the
FXALIAS.UVCOP file as the second input. NOTE, THIS IS NOT
GUARANTEED TO WORK.
INNAME.....Input UV file name (name). Standard defaults.
INCLASS....Input UV file name (class). Standard defaults.
INSEQ......Input UV file name (seq. #). 0 => highest.
INDISK.....Disk drive # of input UV file. 0 => any.
SOURCES....Sources to be baselined using the specified ICHANSEL.
' '=> all except those in CALSOUR. The '-name' usage is
not allowed here.
CALSOUR....Sources to be baselined using BCHAN-ECHAN rather than
ICHANSEL. ' ' => none. CALSOUR(1) is the primary
bandpass and aliasing calibrator.
TIMERANG...Time range of the primary aliasing calibrator to be used.
In order: Start day, hour, min. sec, end day, hour, min.
sec. Days relative to ref. date.
FLAGVER....Version of flag table to be used.
BDROP......Begin channel for alias calibrator unaffected by aliasing
EDROP......End channel for alias calibrator unaffected by aliasing
OUTNAME....Output UV file name (name). Standard defaults.
OUTCLASS...Output UV file name (class). Standard defaults.
OUTSEQ.....Output UV file name (seq. #). 0 => highest unique
OUTDISK....Disk drive # of output UV file. 0 => highest with
space for the file.
BCHAN......Lowest channel number in the input file to fit CALSOUR
sources. 0=> Nchan/8
ECHAN......Highest channel number in the input file to fit CALSOUR
sources. 0=> Nchan - Nchan/8
ICHANSEL...For sources named in SOURCES, selects up to 20 groups of
channels/IF(s) to fit as sets of (Start,end,inc,IF),
i.e., ICHANSEL = 6,37,1,0, 92,123,1,0 for two regions
applying to all IFs. The first group for which
ICHANSEL(2,i) <= 0 ends the list. Defaults: Any IF having
no group assigned to it, gets a group including all
channels. ICHANSEL(1,j) defaults to 1,
0 < ICHANSEL(2,j) < ICHANSEL(1,j) defaults to Nchan.
ICHANSEL(3,j) < 1 or > ICHANSEL(2,j)-ICHANSEL(1,j)+1
defaults to 1.
ICHANSEL(4) <= 0 => this group applies to all IFs.
DPARM......(1) > 0 => do NOT average polarizations in fitting the
(2) > 0 => do NOT average IFs in fitting the aliasing
(3) > 0 => do NOT average times in fitting the aliasing
(4) > 0 => do NOT average antennas in fitting the
(5) > 0 => do full complex aliasing function
< 0 => zero the imaginary part of aliasing function
(6) > 0 => Hanning smooth the aliasing function