on,off position switching offsets



    On,off position switching is done to remove standing waves from the resulting spectra. Tracking the same part of the dish for the off should have the same "ground based" standing waves as the on position (this will not work as well for energy that comes from the sky). Typically people will track a source for 5 minutes, and then spend the next 5 minutes retracking the same portion of the dish ( which is an ra/dec position offset  by 5 minutes + the move time).
    If the off position does not  match the on position track exactly, how fast does the baseline degrade? This is the question that is looked at here.


    project a2340 tracked a 20 degree dec source rise to set for multiple days using the cband receiver. The setup was:


    Each 900 second scan was used to emulate on,off position switching.
The plots show the baseline rms vs on,off distance offsets (.ps) (.pdf):
The image shows the acf's for on/offs (.gifs):


processing: usr/2327/dec09/chkonoff.pro