12meter xband cal values measured 24jun22


Links to PLOTS:

Links to SECTIONS:
Why the cals were remeasured.
The model used to compute the cal values
The parameter values used in the computation
Taking the data
Processing the data
Total power vs time by freq band.
     calRatio (caldif/caloff) vs freq
     Fitting to calRatio vs freq
     Computed Tcal and  tsys vs freq

Why the cals were remeasured.

    The sb and xb receivers were removed to test the qrfh wideband horn. The receivers were re-installed on 24jun22. The attenuators after the cal diode were switched from (7,7 db) to (3,2db) (polA,B). The sband , xband cal attenuator values had been inadvertently switched on the previous installation. With the correct  attenuator values, the cal value is about 30% of Tsys.

Parameters used for Tcal computation

    The values i ended up using for the computations (see below for explanations) were:

value Notes
Tabsorber 305K Tabs 31C @ xbstart and 35.5 at sb finish. Used 32C for xb abs.
Tsky 10K includes any scattered energy. see below
Treceiver 80,70
 polA,B  see below
omt temperature.. a guess.
reflection coef for horn/omt see below
omt absorption

 Taking the data:

Processing the data:

    For each scan the following is done:

The Results

Total power vs time by freq band

    Plotting the cal Deflection total power vs time (.pdf)

Calratio (calDif/calOff) vs frequency

    The 2nd set of plots shows the calRatio vs freq plotted for each scan (.pdf)

Fitting a curve to the calRatios.

   A harmonic fit was  done  to the calRatio vs freq and then the fit was used to compute TCal.

The plots show a fit to the CalRatio measurements (.pdf)

Computed Tcal and Tsys using the cal values.

    The  plots show the computed Tcal and tsys in deg K using the new cal values (.pdf)


processing: x101/220624/xbcal/measure_cal.pro

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