lbw polB cal jumps 04dec05


    The cal value for lbw polB changed on 04dec05. The value of the system temperature changed as well as the gain (which is measured using the cal value). The sefd (which is independent of the cal) remained unchanged.  The Tsys jump in polB occurred with both diode 1 and diode 2 so the problem was after the switch that selects which diode to send to polB.

Looking at cal on/offs taken by users:

    All  of the cal on/offs taken using the interim correlator between 23nov05 and 15dec05 were used to compute Tsys. I limited the scans to those taken in linear polarization since the circular mode has a hybrid which mixes the two channels.  The plots show tsys versus date (.ps) (.pdf):

The daily tsys measurements taken at 1400/1405 Mhz.

    The lbw system temperature is measured (almost) daily  using all the cal combinations.  It was taken at 1400 Mhz until 05dec05 when it was switched to 1405 Mhz (to get away from a resonance in polA at 1400 Mhz).
    The plots show lbw Tsys for jan01 through feb06 (.ps) (.pdf):

Tsys, gain from the calibration scans:

    The lbw calibration scans between jul05 and feb06 at 1415 Mhz were inspected to see if the change in tsys was a real increase in tsys or a result of the cal values changing.

    The plots show lbw calibration scans jul05 to feb06 at 1415 Mhz (.ps) (.pdf):


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