AIPS HELP file for BANDPOL in 31DEC18
As of Thu Jul 19 0:09:26 2018
Type: Adverb (String*8)
Use: To specify the polarization of each IF in a UV data file
where the polarizations have not been labeled correctly
in the file header.
Format: In its simplest form the value is a string of Rs and Ls
or Xs and Ys in which the i-th character denotes the
polarization of the i-th IF. So
BANDPOL = 'RLRLRL '
would specify that the IF numbers 1, 3, and 5 are RR
while IF numbers 2, 4, and 6 are LL.
In general, the value of BANDPOL is a sequence of
polarization groups. Each polarization group consists
of either a single letter (R, L, X, or Y) or a sequence
of the letters R, L, X, and Y enclosed in parentheses
and preceded by an optional repeat count. The repeat
count may be a decimal number or an asterisk. If the
repeat count is omitted it is taken to be 1. An asterisk
means that the following group should be repeated
BANDPOL is interpreted as follows. First every
polarization group with a repeat count is replaced
by n copies of itself where n is the repeat count.
Secondly, all parentheses are removed from the string.
Finally, the resulting string is trimmed to a length
equal to the number of IFs in the file to be processed
and each character is taken to denote the polarization
of the corresponding IF.
Some examples should make this clear.
'3(RL) ' IFs 1, 3, and 5 are RR
IFs 2, 4, and 6 are LL
'*(LR) ' IFs 1, 3, 5, ... are LL
IFs 2, 4, 6, ... are RR
'7XY ' IFs 1, 2, 3, ..., 7 are XX
IF 8 is YY
Null value: ' '
Taken to be equivalent to '*(RL) ', that is all odd-
numbered IFs are RR and all even numbered IFs are LL.
FXPOL........Corrects VLBA polarization assignments