Lbw cal values measured 22apr07

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.

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

    The temperatures used in the computation were:
 

Tabsorber	298 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  9 passes 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  (.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 9 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.
  
• Around 1300 Mhz Tcal absorber has a negative going bump. Tcal sky polB and both Tcal sky and absorber polA have a positive going bump here.
  
• 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). The 1270/1290 birdies that are coming through are from the remy radar.
• 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 aerostat radar and the punta salinas radar.
  
• 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.
  

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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% over the full band.
  
 
• 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). Diode 2 --> polB has a large frequency dependance across the band. After taking the data we found a bad relay in the cal switching box that could cause this (we need to fix it and then after the painting project remeasure the cals).
  

• 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.
  
• 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


The 2nd and 4th plots show diodes going to polB.  The new cal values (solid lines) are about 25% larger than the old cal values (dashed lines). When the cable in the dewar was tightened, more cal would get to the receiver.
 
The 1 and 3rd plots show diodes going to polA. These agree until you get to 1500 Mhz where they start to diverge. The new cal values have less power than the old cal values. This same trend was seen back in 23feb06. The cal values of 23feb06 polA had more power at high freq (gt 1500 Mhz) than the cal values from 24Nov05 (when these diodes were installed).

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