cband 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 6 years.
• The receiver had been brought down to the lab to be worked on a few times during these 6 years..

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

• absorber measurement: morning of 28jun12
• on Sky measurements:
  
• 29jun12  - 16:00 to 17:30
• Lots of clouds during the sky measurements. This may affect Tsys.
  

    The temperatures used in the computation were:
 

Tabsorber	303.7K (87.1F avg temp sensor)
Tsky	8K
Treceiver	from ant test range jun05.
Tscattered	15 K

    The recording and processing steps were:

• the band from 3900 to 6150  MHz was covered in 3 sections:
  
• Set 1: 3950 to 4800 MHz
• Set 2: 4800 to 5700
  
• Set 3: 5600 to 6150 (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  3950 to 6150   MHz data  was resampled to a fixed spacing of (172/1024=.168KHz). This was needed since the  spectra were overlapped.
  
• A robust fit (35th 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 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.
• 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 Tsys from the sky alone is a little hight. This may be that the Treceiver curve may be a little off.
  
• The bottom plot is the cal In kelvins from the Y factor.
• PolB has more ripple than polA
•  The * are spaced every 25 MHz. PolA is black and polB is red.
  

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 3975 to 6075 Mhz.
  
• 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 framse 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 25 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 and new cal values are pretty close to one another:
• The bumps in the cal values for the new data comes from rfi. This was not as prevalent back in 2006.
• Comparing Tsys measurements using 28jun12 and dec08  cals  (.ps) (.pdf):
• The plots show the tsys measurements jan12 -> 17sep12. This data is measured at 5000 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
• The new cal values do not change the system temperature very much.
  

• Stokes Calibration check:
  
• The stokes calibration processing computes deltaG which is the error in the the cal Difference (CalPolA - CalPolB)/(mean(calPolA+calPolB))
• Delta G using the old cal values ranged from .5 to 2.3%. The new cal values did not change this much.
• 
  

Summary

• The new cal values were measured on 28 and 29jun12.
• the new cal values came out very close to the old cal values (so i guess you can go 6 years without remeasuring the cals!!!).
• The cal values were installed on 17jun12
• the cal values were back dated to be valid from 28jun12 (the date of the measurement).
  

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