AIPS HELP file for FQCENTER in 31DEC25

As of Mon Mar 17 0:05:57 2025

HELP SECTION

FQCENTER
Type: Adverb   (Logical,   > 0  =>  true)
Use:  If True, make the output frequency axis of a UV data set be
      referenced to the frequency channel Nchan/2 + 1 of IF 1.
      If False, leave the frequency reference pixel unchanged, or
      change it to pixel 1.0.
Null Value:  true (1)
Tasks:
   Many tasks which copy data have this option.  A frequency reference
   change requires both a simple change in the UV data set header and
   a scaling of the U,V,W values of each sample by the ratio of the
   new to old reference frequencies.

Tasks:
   AVER..........Averages over time UV data sets in 'BT' order.
   BDAPL.........Applies a BD table to another data set.
   BPWAY.........Determines channel-dependent relative weights.
   BPWGT.........Calibrates data and scales weights by bandpass
                 correction.
   DAYFX.........Fixes day number problems left by FILLM.
   DBCON.........Concatenates two UV data sets.
   DFQID.........Modifies UV data changing the indicated FQIDs.
   DIFUV.........Outputs the difference of two matching input uv data
                 sets.
   DQUAL.........Rearranges source list, dropping qualifiers.
   DSORC.........Copies a data set elliminating some source numbers.
   DSTOK.........Drops the cross-hand polarizations.
   FIXRL.........Correctes right vs left polarizations for a list of
                 antennas.
   FUDGE.........Modifies UV data with user's algorithm: paraform task.
   FXTIM.........Fixes start date so all times are positive.
   HAFIX.........Recomputes u,v,w when time is hour angle (UVdata is
                 output of TI2HA).
   MULIF.........Change number of IFs in output.
   NOIFS.........Makes all IFs into single spectrum.
   PHNEG.........Negates a UV datafile's visibility phase.
   REAMP.........Scale visibility amplitudes by IF- or subarray-
                 dependent factor.
   REIFS.........Breaks spectral windows into multiple spectral windows
                 (IFs).
   REWAY.........Computes weights based in rms in spectra.
   REWGT.........Modifies UV data re-scaling the weights only.
   RLCOR.........Corrects a data set for R-L phase differences.
   SWPOL.........Swap polarizations in a UV data base.
   SYSOL.........Undoes and re-does nominal sensitivity application for
                 Solar data.
   TI2HA.........Modifies times in UV data to hour angles.
   TYAPL.........Undoes and re-does nominal sensitivity application.
   UVAVG.........Average or merge a sorted (BT, TB) uv database.
   UVCMP.........Convert a UV database to or from compressed format.
   UVCOP.........Task to copy a subset of a UV data file.
   UVFIX.........Recomputes u,v,w for a uv database.
   UVLIN.........Fits and removes continuum visibility spectrum, also
                 can flag.
   UVLSD.........Least squares fit to channels and divides the uv data.
   UVLSF.........Least squares fit to channels and subtracts from uv
                 data.
   UVMOD.........Modify UV database by adding a model incl spectral
                 index.
   VBGLU.........Glues together data from multiple passes thru the VLBA
                 corr.
   VH2RL.........Converts from linear to circular polarization and vice
                 versa.
   VHMOD.........Compute linear polarization point source model, applies
                 to data.
   VPFLG.........Resets flagging to all or all corss-hand whenever some
                 are flagged.
   WTMOD.........Modifies weights in a UV data set.
   XYMOD.........Compute linear polarization point source model, applies
                 to data.

EXPLAIN SECTION