[daip] reference used in BPASS calibration

[Eric Greisen]

Wasim Raja wrote:
> 
>   Dear Eric,
>     Could you please tell me whether or not the following
>     observation of mine is correct regarding task BPASS in
>     31DEC08 version of AIPS:
> 
>     The reference spectrum for the bandpass calibration of
>     either hands of the antennas is taken as the L-Hand
>     spectra of the reference antenna.
> 
>     My basic wish is to know whether the spectra of the
>     L-Hand and the R-hand are brought to the same level, or
>     whether the referencing is done independently for both
>     the hands.
> 
>     Sorry to bother you with what may be obvious, but frankly
>     speaking, I could not find an exact answer using the
>     Documents readily available -- like the obvious sections
>     in the cookbook, or the web. My observation about the
>     referencing being done using the L-hand band of the reference
>     antenna is based on the fact that the BP-table does not
>     contain entries for the L-hand of the reference antenna.

I think that you are wrong.  The reference antenna is done separately in 
the R and L hand polarizations.  In both polarizations of their 
respective reference antenna, the BP phase will be zero but the 
amplitudes will be the usual sorts of amplitudes.  The two are not 
correctly referenced together - this requires using the cross-hand 
polarizations plus information on the source itself.  Such cross 
referencing is needed for polarization imaging but not otherwise.

I do not know what you mean exactly by does not contain entries.  If the 
entries are missing or blanked then there is a problem with the antenna
and it cannot have been used as a reference.  If by missing you mean 
simply that the phases are 0 (imaginary part 0) then that is expected 
for the reference antenna.  Use PRTAB to look at the bP table - it will 
show you the reference antennas used which may be different in R and L.

Eric Greisen