Lbw cal values measured 28jun12

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.
Diagnostics

Why the cals were remeasured.

• the lbw stokes calibration on  27may12  showed that the cal difference polA,polB were incorrect by 15-17% (DeltaG). This error went away when the data was reprocessed with the new cal values.
  
• Previous measurements of  DeltaG showed:
• 09feb11,08feb11,25jan11,16jan11  deltag ok
• 23nov10: deltag off by 11%
• 30jun10: deltag ok
• TsysPolA - TsysPolB jumped down by 3 K around 10feb12. 
• Other TsysPolA-TsysPolB jumps:
• 22apr11 TsysPolA-TsysPolB jumps up by 4K.
• 28oct10 to 10dec10 TsysPolA-TsysPolB jumped down than back up by 4K
• Both of these jumps look like they occurred after a dewar warmup, cooldown.
  

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

• absorber measurement: morning of 28jun12
• on Sky measurements:
  
• 28jun12 -16:00 heavy clouds, lightning in the distance, no local rain.
• 01jul12  - 11:00  clear, light clouds.
  

    The temperatures used in the computation were:
 

Tabsorber	303.7K (87.1F avg temp sensor)
Tsky	5 K
Treceiver	from test shack feb03
Tscattered	15 K

    The recording and processing steps were:

• The band 1120 to 1750 MHz was covered simultaneously  using 5 mock spectrometers with 172MHz, 1024 channels each.
  
• The 25 Hz hardware winking cal was used.
  
• Spectra were sampled at 2 milliseconds
• Each 20 millisecond calOn,Caloff block was averaged (throwing out spectra before after each cal transition)
• The median in each channel (over the 120 seconds) was used as the average value for calDeflection/Tsys
  
• The  1120 to 1750 MHz data  was resampled to a fixed spacing of (172/1024=.168MHz). This was needed since the 5 spectra were overlapped.
  
• A robust fit (8th order harmonic, 1st order polynomial) was done to the ratio data (4001 points). For the sky fits, 4 points about each excluded point were also removed.

   The on sky processing for 28jun12,01jul12 were processed separately and then averaged for the final result.

    The results of the reduction are:

• Fits to the Average CalDeflection/Tsys  and HcorCal in Kelvins(.ps)  (.pdf):  This shows the average Tcal/Tsys data with the fits over plotted in red.
• Page 1: Tcal/Tsys plots
  
• The top two plots are on the absorber (polA,polB)
• The bottom two plots are on the sky. black is the 28jun12 measurement, red is the 01jul12 measurement
• 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(172bw/1024chan*120secs)=.000
• The abs plots are close to this, the sky plots are about 6 times larger.
  
• Page 2: 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. 
• The 28jun,01jul fits were averaged.
  
• These are the values that will be used for the cal.

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)

• Each 10 second set was processed similar to the hcorcal above.
• The ratio (calDifX/caloffX was computed (X is each cal type) for each 10second set and then a robust fit was done (same as hcorcal above).
  
• For each of the "other cals" (hcal,hxcal,h90cal,lcal,lcorcal,lxcal,l90cal)" the ratio (calDifX/calOffX)/(HcorCal) was computed. The hcorcal value used was interpolated (in time) from the 3 sets of hcorcal measured.
• The hcorCalFit in kelvins from the hcorcal measurements (see above) was then multiplied int the other cal fit to give each caltype  in Kelvins.
  

     
  The results of the reduction are:

• OtherCals/Hcorcal and the fits (.ps)  (.pdf):
• These plots show the ratio of the otherCal/hcorcal data and the fits to this ratio.
  
• Page 1: high cals
• page 2: low cals
• top frame polA,bottom from polB
  
• Over plotting all of the cals (in deg K) (.ps) (.pdf). 
  
• Top frame has the high  cals, the bottom frams has the low cals
• The solid lines show polA, the dashed lines show polB.
• The colors show the different cal types.l
• the + on the black plot on the upper frame show the 10 MHz samples used for the cal lookup table.
• 
  

Diagnostics:

• 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.
  
• 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
• You can see that the cal values for PolA changed a lot while the cal values for PolB remained about the same.
• The polA values changed whether polA was being fed by diode 1 or diode2.
• This shows that the cal change was after the diode multiplexor in the cal (postamp) chassis.
  
• The diode outputs did not change.
• The change was probably the connector, cable, or coupler from cal chassis to rfi injection.
  
• Comparing Tsys measurements using 28jun12 and dec08  cals  (.ps) (.pdf):
• The plots show the tsys measurements jan12 -> 09aug12
• Tsys is plotted using the old cal values (polA, polB) and then replotted using the new cal values (polA, polB)
• A horizontal dashed lines shows 30K
  
• Top Frame: hcal (diode1 -> polA, diode2->polB)
• PolA (black,red) differ while polB (green,blue) remain the same
• 2nd frame: hcorcal (diode 1->polA, diode1 ->polB)
• The results are similar, polA changes, polB is the same.
• So the diodes did not change.
• Bottom frame (TsysPolA - TsysPolB)
• Black is Tsys for  the old cals, red is tsys for the new cals.
• there was a jump down in the tsys value around 07feb12. After that there was a slow decrease in Tsys over the year.
• If you inserted the new cals around this jump, tsys would have remained constant (except for the slow drift)

• Stokes Calibration showed a a large error with (CalA-CalB)/(mean(CalA+CalB)) with the old cal values
  
• The stokes calibration processing computes deltaG which is the error in the the cal Difference (CalPolA - CalPolB)/(mean(calPolA+calPolB))
• Calibration data was taken on 27may12 on B2209+08. It was processed with the old cal values, and then reprocessed with the new cal values.
  
• DeltaG values weremeasured at 1415,1550,1610, and 1666 Mhz
  
• B2209+08 with Old Cal values (.ps) (.pdf)
• DeltaG: -.136, -.152,-.196, -.13
  
• B2209+08 with New cal values (.ps) (.pdf)
• DeltaG: .007,.004,-.014,.002
• The new cal values make DeltaG close to 0.
  
• With the old cal values deltaG was negative. The cal measurments showed that it was polA that was too small (not polB being too large).
  

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