Lbw cal values measured 06aug04


Links to PLOTS:
hcorcal value versus freq from sky and absorber
spectra of hcorcal on/off-1 on sky
power levels during hcorcal measurements

Ratio of other cals to hcorcal tracking blank sky.

Compare Tsys using the old and new cal values.

Links to SECTIONS:
Measuring the high correlated cal using blank sky and absorber
Measuring the other cals on blank sky relative to the high correlated cal.
Has the cal value stopped drifting??

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 06aug04 on the telescope using  the sky/absorber technique. The telescope tracked  blank sky and used 3 second cal on/offs.  The data was taken with the radar blanker on for both the sky and absorber.
    Tsys for polB  started to drift on 24apr04. It continued to drift 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 measurement. It was coming from after the diodes. After waiting for  polB to stop drifting, we remeasured the calvalues using sky and absorber.
    The Trcvr measured on the antenna test range in feb03 were used to remove the Trcvr.

    The temperatures used in the computation were:
Tabsorber 301 K
Tsky 5 K
Treceiver from test shack
Tscattered 15 K

Each frequency band was measured 9 separate times on the absorber and 9 separate times on the sky. For each measurement the calon/off-1 spectrum was  computed.   A 3rd order polynomial was fit to this data to generate the cal values (throwing out any data points greater than 2 sigma on the first iteration of the fit). The cal Value versus frequency plots show the results.

    The spectra of calOn/Caloff-1 for the 9 sky measurements  shows the spectra for the on sky measurements. 100 Mhz junks at a time were taken. Pol A is clean in the 1300 to 1400 Mhz band while  pol B has some gain jumps in this region. The radar blanker was on during this measurement. This same behavior was seen in polB in mar03. Maybe polB is saturating somewhere and not recovering??

    The final plot has the power levels during the measurements.

processing: x101/040806/hcorcal/,,,

Measuring the other cals using sky and the high correlated cal from above.  (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 calOn/calOff -1  spectra was computed for each measurement (giving cal in units of calOff or Tsys).  Each of these 25 Mhz band passes was cumfiltered. This was done on the 6 loops of the same freq band (256 channels *6 numbers). The total power was computed and then the ratio of each cal value relative to the hcorcal was computed (via interpolation of the 3 measurements). These values were used to generate the cals table (after multiplying by the hcorcal in kelvins). No polynomial fit to the data was done. The figures show the other cals relative to Tsys and the hcorcal:
processing: x101/040806/othercals/,

Has the cal value stopped drifting??  (top)

    The daily Tsys measurements showed the initial problem with the cal values. I took these values and recomputed the value of Tsys using the new cal values for the time period 4jun04 thru 12sep04. The plots show Tsys  versus day number of year for this period.