Notes on Data Reduction

  Each subsystem, being a separate spectrum, is read into one of the SPECX buffers (`stack' positions). The noisy channels on the edges of the every subband should be dropped using the drop x y command. x and y should both be typically 15 channels for the 500 or 760-MHz configurations --- more for the higher resolution modes. The subbands can then be joined into a contiguous spectrum using the command merge y. Changing the parameter to ` n' prevents the software from correcting the DC offsets between the subbands. Note that for broadband sources, this generally gives flatter baselines, so merge n is preferred. Note that the single command das-merge combines the actions of drop and merge; it will automatically drop a certain fraction of the overlapping channels, the default being half.

The subbands (or `quadrants', as SPECX calls them) that make up each subsystem may, if really necessary, be tweaked (eg multiplied, offset, etc) before merging by masking the appropriate one out using the SPECX command set-quad.