Sbw cal values measured 26sep08

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.
Comparing old, new cal values

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Why the cals were remeasured.

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

    The temperatures used in the computation were:
 

Tabsorber	301 K
Tsky	6 K
Treceiver	from test shack sep01
Tscattered	14 K

    The sbw filterbank breaks the band up into: 1.7 to 1.88, 2.04 to 2.40, an 2.6 to 3.10 Ghz. The 100 Mhz bandwidth of interim correlator ended up taking 5 separate measurements to cover this range: (1700-1800,1780-1880, 2040-2140,2100-2300, and 2600-3100).
    This range was covered 6 times on sky and on 6 time on absorber. The processing wants contiguous data so the following processing was done for each of the 5 contigous frequency sections:

• The ratio (CalOn-CalOff)/CallOff was computed for the data.
• Each spectra covering the band of this section (100,100,100,200,500 Mhz) was then fit to an nth 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 robust average of the  6 passes for each section 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:

• Fits to the Average CalDeflection/Tsys.
  
• This shows the average Tcal/Tsys data with the fits over plotted in red. The top two plots are on the absorber (polA,polB) while  the bottom two plots are on the sky.  The averages were made from the 6 passes through the frequency band.  The units are Tsys (about 30K for sky and 300 K for absorber). The fitRms is computed for the fraction of the spectra used in fitting. The rms and fraction of spectrum used are printed on each plot.
  
•  The radiometer equation should give:
rms=sqrt(2ratio)./sqrt(25e6bw/256chan*3secs*9loops*2hanning)=.0006
The absorber fits match this. The sky fits are about 6 time larger. This is because the fits are not fitting the 1 MHz standing wave from the dish. This is ok since that ripple should not be in the cal value anyway.
• The Hcorcal in kelvins (individual sections):
  
• The first two plots show the cal fits in kelvins measured from the Sky, absorber, and the sky, absorber ratio (Y factor). The top plot is polA, the middle plot is polB. The dashed line is the receiver temperature used for calSky.
•  The calAbs and calY agree while the calSky is different. The calsky Dc level can be shifted up or down by changing the amount of Tscattered.
  
• The Trcvr curve will have the largest affect  on Calsky.
• The bottom plot is the cal In kelvins from the Y factor. The * are spaced every 10 MHz. PolA is black and polB is red. These are the values that will be used for the cal.
• Hcorcal in kelvins (all bands):
• This shows the hcorcal for polA (black) and polB (red) for the entire bandpass. The fit to the averages has been evaluated every 20 Mhz. The spaces are where no data was taken.
  
• The green, blue lines are receiver temperatures for polA,polb.
  

    Diagnostics:

    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.

• CalDeflection/Tsys for each pass.
• The first page shows on absorber for the 9 passes through the receiver band. The top plot is polA while the bottom plot is polB. The spectra have been offset for plotting purposes. The units are Tsys (on absorber it is about 300K). The dashed vertical line shows the start of each 100 MHz integration (4sbc*25MHz each). Very little of the rfi is coming through the absorber.
  
• The second page shows on the sky  for the 9 passes through the receiver band. The top plot is polA while the bottom plot is polB. The spectra have been offset for plotting purposes. The units are Tsys (about 30K on the sky). The dashed lines show the 100 MHz boundaries (that were taken separately). The birdie around 1240/1260 are the  punta salinas radar. The below 1400 MHz looks like our old resonance ?
  
• Fits to the CalDeflection/Tsys for the each pass.
• 9 passes thru the frequency band. This over plots the fits to each pass (6144 points covering the 600 MHz.). The absorber fits vary by more than the Sky fits since deltaTsys is a larger fraction of the cal when you are on absorber.

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

• hcorcal(on,off)
• hcal(on,off),hxcal(on,off),h90cal(on,off)
• hcorcal(on,off)
• lcorcal(on,off),lcal(on,off),lxcal(on,off),l90cal(on,off)
• hcorcal(on,off)

   The results of the reduction are:

• The average calValues in kelvins and the fits.
  
• The fits to the 4 passes have been averaged together and then multiplied by the hcorcal fit (in kelvins). There are 14 plots. 7 cals each with polA and polB. The red lines are the fits to the data. 
  
 
• Over plotting all of the cals (in deg K).
  
• The top plot is the high cals and the bottom plot is the low cals. The solid lines are polA while the dashed lines are polB. 
  

Diagnostics:

• CalDeflectionCalX/calDeflectionHcorcal for the 4 passes.
•  There is 1 page for each calType (7 pages).
  
• The top plot is polA and the bottom plot is polB. T
• The 4 passes through the freq range are over plotted with an offset. The units for the y axis are TcalHcorcal since each of the cal deflections have been divided by the hcorcal deflection.
  
• Fits to the CalDeflX/calHcorcalDefl for the 4 passes. This over plots the fits to each pass showing any variations in the fits by pass

Compare old,new cal values

• Solid lines are the new cals
• Dashed lines are the old cal values (2004)
• The black lines are diode 1
• the red lines are diode 2.
• The cal values have increased. This will increase the Tsys (relative to using the old cal values).

• Tsys has gone from 24 K to about 34K. The old cal values were too low.
• The spread in Tsys for different cals is much smaller for the new cals.
  

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