Lbw cal values measured 08dec08

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.

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Why the cals were remeasured.

• The cal values measured gave a system temperature with polA about 8 kelvins higher than polB.
  
• The cal values for polA and B (hcorcal) were very close.
•  In the past there had been a 2 Kelvin difference between polA and polB cals for hcorcal.
  
• If the linear circular switch remained in circular while the data was taken, then this could explain the values of the cals being the same.  The header values for the file said that we were using linears (the correct setting).

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

    The temperatures used in the computation were:
 

Tabsorber	299 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 9 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 robust average of the   passes was  computed (iterating and throwing out outliers). There was some jumps in some of the passes. These were not included in the average. The passes used to compute the average were:

• polA: passes [1,4,5,7,8] counting from 0
• polB: passes [0,2,3,5,6] counting from 0
  

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  (.ps)  (.pdf):  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 5 selected 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 (.ps) (.pdf).
• 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.

• CalDeflection/Tsys for the 9 passes thru the frequency band (.ps)  (.pdf).
• 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).
  
• Some of the 1200 to 1300 Mhz rfi is getting in while on absorber.
  
• Some of the passes have jumps 100 Mhz wide.
• The integrations are done in  100 Mhz chunks.
  
• After 100 Mhz we reconfigure (mainly the filter bank and the synthesizer) to move to the next 100 Mhz.
• The jumps mean that the cal is changing or Tsys is changing (probably Tsys).
  
• The worse jumps are 1320-1420 PolB.
  
• The filter sequence used near this band is:
• 1220-1320  filter 5 1100 to 1800
• 1320-1420  filter 3  1230 to 1470
• 1420-1520 filter 5 1100 to 1800..
  
• So maybe the 1230 to 1470 filter switch is not always closing well.
  
• 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 9 passes thru the frequency band (.ps) (.pdf). 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. This includes the fits that were not used in the average.
  

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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 (.ps)  (.pdf):  The fits to the 6 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. The fit rms's are better than 1.5% over the full band. Some of the passes with jumps in them were not used in the average.
  
 
• Over plotting all of the cals (in deg K) (.ps) (.pdf).  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. There are two sets of lines that follow each other. That is because the same diode always feeds two types of cals (e.g. diode1 goes to polA for hcorcal and for huncorcal).
  

• CalDeflectionCalX/calDeflectionHcorcal for the 6 passes (.ps)  (.pdf). There is 1 page for each calType (7 pages). The top plot is polA and the bottom plot is polB. The 6 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. Some of the passes with jumps in them were not used in the average.
  
• Fits to the CalDeflX/calHcorcalDefl for the 6 passes (.ps) (.pdf). This over plots  the fits to each pass (6144 points covering the 600 MHz.).
  
• Over plotting the new and old cal values (.ps) (.pdf). The solid lines are the new cals. The dash lines are the old cal values. The plots are:
• Top HiCalsPolA: black Diode1 -> polA, Red diode2->polA.
• 2nd HiCalsPolB: black Diode1->polB, Red diode2->polB
• 3rd LoCalsPolA: black Diode1 -> polA, Red diode2->polA.
• 4th LoCalsPolB: black Diode1->polB, Red diode2->polB
• Comparing Tsys measurements using 26sep08 cals and the 08dec08 cals (.ps) (.pdf):
• The top plot is Tsys measured using the 26sep08. The higher set of points is polA. The lower is polb.
• The bottom plot is Tsys measured using the 08dec08 cal values. TsysA and tsysB are now much closer. There is still a difference of 1-2K in the Tsys. This may have to do with the resonance at 1400 Mhz in Pola.
  

PolA cal is not about 2K  lower than polB. the 26sep08 measurement had them nearly equal which gave a large polA Tsys.  

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