alfa performance at OH with 10db amps in

06may05
links to plots:

comparison of the system performance for alfa and lbw at OH (.ps)  (.pdf) (no amps in)
comparison of the system performance for alfa and lbw at OH (.ps)  (.pdf)   (with amps in)

    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 performance was measured using the continuum source CTA21 (B0316+162. 7.2 Jy at  1666 Mhz). After these measurements   amplifiers (about 10db)  were installed before the filter bank to improve the noise figure of the system. The system performance was remeasured on 06may05 using the continuum source B0428+205 (3.8 Jy at 1666 Mhz).  For each of these dates the procedure was:

    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.


01apr05 with no amplifiers installed:

    The plots show the comparison of the system performance for alfa and lbw at OH (.ps)  (.pdf) (no amps installed).


06may05 with the amplifiers installed:

    This used the source B0428+205 (3.8 Jy at 1666 Mhz). The power levels were adjusted off source.
The plots show the comparison of the system performance for alfa and lbw at OH (.ps)  (.pdf) (with amps installed).
  • Fig 1: This shows srcDeflection/Offsrc (G/T). Black is polA and red is polB. The top plot is pixel 0, the middle plot is pixel 1, and the bottom plot is lband wide. The two polarization's of alfa differ now differ by about 30%. This source is not polarized at lband. Using the fluxes of 3.78 Jy, the sefds for the measurements are: Alfapix0: 4.4,5.7 alfaPix1:6.2,9.9  Lbw: 2.5,2.4 Jy. By comparing the lbw sefd's between 01apr05 an 06may05, the sefd's (source fluxes) probably have an error of 5%.
  • Fig 3: This shows (G/T alfa)/(G/T lbw) for pixel0 (top) and pixel 1 bottom. The average values are:  .56,.42 pixel 0 and .5,.25 pixel1.

  • Summary:

        The results of the measurements are:
     
    Measured Sefd
    measurement lbw
    (PolA,B)
    Pixel0
    (PolA,B)
    Pixel1
    (PolA,B)
    noAmps  (01apr05) (2.4 ,2.3) (4.3,6.0)
    with Amps (06may05) (2.5 ,2.4) (4.4,5.7) (6.2,9.9)
    (G/T alfa)/(G/T lbw)
    Pixel 0
    (PolA,B)
     Pixel1
    (PolA,B)
    no Amps 01apr05 (.55,.37)
    with Amps (06may05) (.56,.42) (.40,.25)

        Adding the amplifiers may a small improvement to polA and a larger improvement to polB.
    The polB/polA performance ratios are:

    My guess is that polB pixel 1 could use  a higher power level (and maybe some of the other outer pixels).

        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 (using the data with the amps in):

    Lbw must also move between positions. For a1851 this was taking about 5% longer. The relative sensitivity is:     The comparisons are then:
    processing: x101/050401/doit.pro, x101/050606/doit.pro

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