xband 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 cals had not been measured for 8 years.
• Tsys was higher than expected (38-40 K).

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

• absorber measurement: morning of 28jun12
• on Sky measurements:
  
• 01jul12  - 11:00 am light clouds.
  

    The temperatures used in the computation were:
 

Tabsorber	303.7K (87.1F avg temp sensor)
Tsky	8K
Treceiver	from test shack mar04
Tscattered	15 K

    The recording and processing steps were:

• the band from 7900 to 10100 MHz was covered in 3 sections:
  
• Set 1: 7900 to 8760 MHz
• Note: the last band of the first set was mispositioned in freq so it was not recorded.
  
• Set 2: 8715 to 9605
• Set 3: 9555 to 1084 (only 4 mock boxes used). 
• The mock boxes used 172 MHz bw. sets 1,2 used 7 boxes, set 3 used 4 boxes.
  
• 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  7900 to 10100  MHz data  was resampled to a fixed spacing of (172/1024=.168KHz). This was needed since the  spectra were overlapped.
  
• A robust fit (28th order harmonic, 1st order polynomial) was done to the calDeflection/Tsys  ratio (13000+ points). For the sky fits, 4 points about each excluded point were also removed.

    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.
• The dropout is the last band of set 1 that was not recorded correctly.
  
• 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)=.0003
• The abs plots are close to this, the sky plots are about 10 times larger.
• The ripple is probably coming from the cal (coupler,cable?).
  
• 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.
• All 3 of the measurements agree with one another. 
• The bottom plot is the cal In kelvins from the Y factor.
• The ripple period is about 180 MHz. It could be a  reflection in air of about .83Meters or  .6 meters in a median with n=1/.7.
•  The * are spaced every 25 MHz. PolA is black and polB is red.The old cal table was spaced by 100 MHz. This did not sample the cal ripple often enough.
  

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 10 second 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. Each cal type measurement was re sampled to a fixed frequency grid covering 7900 to 10100MHz.
  
• 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
• The old cal values measured on the antenna test range did not see the large ripple in the cals (probably because of course sampling).
• PolB seems to have changed more than polA.
  
• Comparing Tsys measurements using 28jun12 and dec08  cals  (.ps) (.pdf):
• The plots show the tsys measurements jan12 -> 09aug12. This data is measured at 8800 MHz.
  
• 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)
• 2nd frame: hcorcal (diode 1->polA, diode1 ->polB)
• Currently the new cals have TsysA,B the same value (about 35K). With the old cals they were higher and differed by about 2K.
  
• 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 polB  tsys value around 18jul12. This was after a receiver warmup,cooldown

• Stokes Calibration check:
  
• 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 04may12 on B0518+165. It was processed with the old cal values, and then reprocessed with the new cal values.
  
• DeltaG values were measured at  8500,8800,9000, and 9200 MHz.
  
• B0518+165 with Old Cal values (.ps) (.pdf)
• DeltaG: -.136, -.152,-.196, -.13
  
• B0518+165 with New cal values (.ps) (.pdf)
• DeltaG: .007,.004,-.014,.002
• Below shows the change in delta g:

• Freq	DeltaG OldCals %	DeltaG NewCals%
  8500	-15.6	-.4
  8800	-14.2	-8.8
  9000	-11.5	-.9.3
  9200	-13.5	-7.6

  
  
• The new cal values have improved the error in CalA-CalB.
• Ripple across the band.
• There is a large ripple in the CalDeflection/Tsys bandpass. It as a period of about 180 MHz. This could be a reflection of about .6 meters if the velocity in the medium is .7 c.
  

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