Lbw cal values measured 10jun05


Links to PLOTS:
     Fits to the Average CalDeflection/Tsys  (.ps)  (.pdf):
     Hcorcal in kelvins (.ps) (.pdf).
           CalDeflection/Tsys for the 9 passes (.ps)  (.pdf).
           Fits to the CalDeflection/Tsys for the 9 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 6 passes (.ps)  (.pdf)
           Fits to the CalDeflX/calHcorcalDefl for the 6 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 jumped on 24apr04 (more info). It then  drifted until the first of jun04. This drifting was in the polB measurement. It did not matter whether diode1 or diode2 was feeding polB.  The sefd was measured for polA and polB using an unpolarized source and they remained constant. So the drift was in the cal value. It was somewhere after the diodes since both diodes gave the same result. The drifting slowed down in jun04. We  remeasured the cal values in aug04. A slow  drift in Tsys  continued  into 2005. You can see this in the   TsysPola-TsyspolB plots.

    On 16may05 tsys for lbw started jumping (more info).  After some diagnostics it was decided that something was loose in the lbw dewar. It was warmed up and opened on 01jun05. During this inspection, the polB cal cable in the dewar was found to have a crack where it connected at the inside of the dewar. It was then repaired.

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 10jun04  on the telescope using  the sky/absorber technique.  The sky was remeasured on 13jun05 because of rfi on the 10th. The absorber data came from 10jun05 and the sky data came from 13jun05 was used for the data reduction.  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.

    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 9 times on absorber and 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 .

    After examing the fits,  3 passes in polB (while on absorber) were excluded because of jumps in the 1320 to 1420 Mhz band. A robust average of the  passes was then 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/llb/cals/jun05/hcorcal/,,,

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

    The high correlated cal was measured above using sky and absorber as the hot and cold load. The other cals were then measured relative to the high correlated cal. Blank sky was tracked 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 6 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 spectra for the 6 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 results of the reduction are:

processing: x101/lb/cals/jun05/othercals/,,,