Basic Information on uvspect

Task: uvspect
Purpose: Analyse uvdata spectra and plot amplitude & phase spectra
Categories: uv analysis, plotting

UVSPECT is a Miriad task to analyse and plot visibility spectra.
Plot Amplitude and Phase versus channel, frequency or velocity.
The default is to average the selected uvdata for all baselines
and polarizations. UVSPECT does not apply the gains, or bandpass
corrections when plotting the data.

Key: vis
The input visibility file. No default.

Key: device
PGPLOT device (e.g. /retro, plot.plt/im for hardcopy on a Vax,
or  /sunview, plot/ps for harcopy on a Sun).  No default.
See documentation on the device keyword for more information.

Key: interval
Averaging interval in minutes. Default is no averaging.

Key: select
Standard uvdata selection. Default is all visibilities. See
documentation on the select keyword for more information.

Key: line
Line type of the data in the format
  type,nchan,start,width,step
Here "type" can be `channel', `wide' or `velocity'.
Default is all channels.

Key: fmode
Flagging type to plot. Set fmode=a to plot flagged and unflagged
data. fmode=u to plot unflagged data, fmode=f to plot flagged data.
Default is to plot all data.

Key: fft
fft is a character string describing the FFT processing options.
Default fft=' ' does no FFT processing. Other options take the
complex FFT for each record and each spectral window before
averaging the data.
   +    The sign of the exponent in the FFT.
   -    The sign of the exponent in the FFT.
   s    Add a phase gradient of pi per channel before the FFT
        This produces a half channel shift after the FFT.
   q    Quad swap the input to move the center to the 1st point.
   h    Hanning smooth the output.
Use fft=-qsh to make frequency spectra from HATCREEK correlator
lag data with the lsb and usb of LO1 adjacent for each corf.
The input uvdata must be the default all spectral channels with
the number of channels in each window being a power of 2.
Other options to take the FFT of any input line type are possible
but not yet implemented.

Key: hann
Hanning smoothing length (an odd integer <15). Is applied after
averaging over time. Default is no smoothing (hann=1).

Key: xrange
Plot range in the x-direction (in channels or km/s according to
the linetype selected). Default is to self-scale.

Key: amprange
Plot range for amplitude in the y-direction (in intrinsic units).
Default is to self-scale.

Key: phirange
Plot range for phase in the y-direction (in degrees).
Default is (-180,180) degrees.

Key: mode
Mode can be 'inter' or 'batch'. Default is inter. In either mode,
the user is prompted for options after each plot on a non-hardcopy
device. The options are applied to the current spectrum, which can
then be replotted. mode=inter displays the cursor. Type the first
character and <cr> to select option. The cursor handling is network
dependent, and the character and <cr> may need to typed several times.
Options:
  <cr>   - [Left Mouse]   go to next time average.
  Device - [Middle Mouse] enter new plot device.
  Quit   - [Right Mouse]  exit from task.
  Limits - change plot limits.
  Channel - change x-axis to channel number in the line keyword.
  Velocity - change x-axis to velocity.
  Frequency - change x-axis to frequency.
  Replot - replot current spectrum.
  Position - display cursor position. (if device supports a cursor)
  Write - write out current spectrum to an ascii file.
  End - end of options, get next average.
The original inputs are restored for the next time average.

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