alfa performance at OH (no 10db amps)

links to plots:
 comparison of the system performance for alfa and lbw at OH (.ps)  (.pdf)

    A filter bank was installed in the alfa receiver in mar05 that allowed switching between the 300 Mhz filters and filters that let you look at the OH line. On 01apr05 the system m performance was measured using:

    Since the alfa cals do not work at 1666 Mhz  the metrics used were srcDeflection/Tsys (G/T) and the ratio of G/T for alfa and lbw.

    The plots show the  comparison of the system performance for alfa and lbw at OH (.ps)  (.pdf)

    The only question with these measurements are the low values for the off source power. Lbw is probably ok since 3 db below the optimum power level does not increase Tsys. I doubt that it should matter with alfa either.

    The original reason for the oh filters were for comet observations that do a hexmap about the comet nucleus.  With alfa this could be done 7 times faster (if the outer beams were in the correct position). The effectiveness is determined by the square of the ratios of the sefd's. The numbers to use are:

Lbw must also move between positions. For a1851 this was taking about 5% longer. The relative sensitivity is:     The comparisons are then:
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