Lbw cal values measured 06jul06


Links to PLOTS:
     Fits to the Average CalDeflection/Tsys  (.ps)  (.pdf):
     Hcorcal in kelvins (.ps) (.pdf).
           CalDeflection/Tsys for the individual  passes (.ps)  (.pdf).
           Fits to the CalDeflection/Tsys for the individual passes (.ps) (.pdf).
       The average calValues in kelvins and the fits (.ps)  (.pdf):
        Over plotting all of the cals (in deg K) (.ps) (.pdf).
           CalDeflectionCalX/calDeflectionHcorcal for the 7 passes (.ps)  (.pdf)
           Fits to the CalDeflX/calHcorcalDefl for the 7 passes (.ps) (.pdf).
           Over plotting the new and old cal values (.ps) (.pdf).

Links to SECTIONS:
Why the cals were remeasured.
Measuring the high correlated cal using blank sky and absorber
Measuring the other cals on blank sky relative to the high correlated cal.

Why the cals were remeasured.

     Tsys for polB has jumped a few times in the past (see lbw polB jumps). On 16jun06 the lbw dewar was warmed up. Inside the dewar an sma connector for calPolB was found to be loose. After tightening the connector and recooling the dewar, the amount of calpolB getting into the receiver had increased.

Measuring the high correlated cal using sky and absorber: (top)

    The high correlated  cal value (diode 1 going to polA and polB) for lband wide was measured 06jul06 on the telescope using  the sky/absorber technique.  The absorber was done about 8 am. The hcorcal sky was done around 4am. The observations used 3 second calon followed by 3 second cal off. For the sky observations, blank sky was tracked. In both cases (sky and absorber) the faa radar blanker was used as well as the lbw filter bank.

    The temperatures used in the computation were:
Tabsorber 300 K
Tsky 5 K
Treceiver from test shack feb03
Tscattered 15 K

    The band 1120 to 1720 Mhz was covered 10 times on absorber and 10 times on sky. The ratio (CalOn-CalOff)/CallOff was then computed for the data. Each spectra of 600 Mhz (6144 points) was then fit to an 8th order harmonic and 1st order polynomial (the order was chosen to include the ripples in the caldefl/Tsys spectra). The fit was iterated throwing out points whose residuals were greater than 3 sigma . Whenever a point was excluded, 5 points adjacent to the fit were also excluded . A problem was found in the cal values measured using the 25 Mhz bandwidth of sbc4. The cal/Tsys ratio came out low for all 25 Mhz bands that this sbc measured. The 25 Mhz sections from sbc 4 were not included in the fits.

    A robust average of the  10 passes was  computed (iterating and throwing out outliers). The average spectra was then fit with the same function. See reducing the cal data for more info on the reduction.

    The results of the reduction are:

    The first set of plots show the calOn-caloff/caloff for each pass through the data. The second set over plots the fits to each pass to see how stable the system is.
processing: x101/lb/cals/jul06/hcorcal/,,,

Measuring the other cals using sky and the high correlated cal (top)

    The high correlated cal was measured (see above) using sky and absorber as the hot and cold load. The other cals were then measured relative to the high correlated cal on 06jul06 starting around 05:30. Blank sky was tracked, the filter bank was used, the radar blanker was on,  and the following cal sequence was run:     100 Mhz at a time was measured (4 by 25Mhz) going from 1120 to 1720 Mhz. The cal was cycled on/off for 3 secs at each step.  The entire frequency range was repeated 7 times.
    The ratio (calOnX-calOffX)/caloffX was computed (X is the other cals) and then it was divided by (calOnHcor-calOffHcor)/calOffHcor). A spectrum for the entire pass was then constructed of the other cals relative to the hcorcal. The spectral fits for the 7 passes were averaged. The average spectra was  multiplied by the hcorCal value in kelvins (this removed the hcorCal shape). The resulting spectra was fit with an 8th order harmonic and 1st order polynomial. For more info see computing the cal value.
    The problem with sbc 4 seen in the hcorcal data was not present. This is probably because we are dividing by the hcorcal data. There may still be a problem if the sbc 4 data is not linear.

   The results of the reduction are:

processing: x101/lb/cals/feb06/othercals/,,,