cband cal values measured 10jun05

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 temperatures used in the computation were:
 

Tabsorber	301.5 K
Tsky	3 K
Treceiver	from rcvr test shack
Tscattered	15 K

    The band 4000 to 6000 MHz was covered 9 times on absorber and sky. The ratio (CalOn-CalOff)/CallOff was then computed for the data. Each spectra of 2000 Mhz (20480 points) was then fit to an 23rd 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 . Some regions of some passes were completely excluded because of rfi.

    A robust average of the  passes was then 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  (.pdf) (.6mb):  This shows the average Tcal/Tsys data with the fits overplotted in red.The top two plots are on the absorber (polA,polB) while  the bottom two plots are on the sky.  There are 9 passes through the frequency range averaged..  The units are Tsys (about 25K 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 4 times 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 spikes every 25 Mhz in the sky ratio is caused by the bandpass edges and the division. These points are excluded by the fitting process.
• The Hcorcal in kelvins (.pdf) (.6mb) :
• The first two plots show the cal fits in kelvins measured from the Sky, absorber, and the sky,absorber (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 not so close.
• The bottom plot is the cal In kelvins from the Y factor. The * are spaced every 20 Mhz. PolA is black and polB is red.  This is diode 1 being fed to both polA and polB. The cal value for polB is about 25% higher than polA. This may come from the directional couplers (that couple the cal into the  RF signal) having different coupling constants. These are the values that will be used for the cal.

• CalDeflection/Tsys for the 9 passes (.pdf) (3mb)  :
• 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 is about 300K). You cans still see some interference in the data on absorber.
• The second age 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 25K on the sky).
• Fits to the CalDeflection/Tsys for the 9 passes (.pdf) (1.5mb) : This over plots  the fits to each pass (20480 points covering the 2000 Mhz.).

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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 (.pdf) (2Mb) :  The 3 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 spectra that have Diode2->polB/diode1->polB has more frequency structure than the other ratios.

 
• Over plotting all of the cals (in deg K) (.pdf) (1.2Mb) .  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). These pairs do not track as well for the low cals.

• CalDeflectionCalX/calDeflectionHcorcal for the 3 passes (.pdf)(4.6Mb) . There is 1 page for each calType (7 pages). The top plot is polA and the bottom plot is polB. The 3 passes through the freq range are overplotted with an offset. The units for the y axis are TcalHcorcal since each of the cal deflections have been divided by the hcorcal deflection. You can a large frequency dependence for Diode2/diode1 (up to 100 % over the 2Mhz band).
• Fits to the CalDeflX/calHcorcalDefl for the 3 passes (.pdf) (2.1Mb) . This over plots  the fits to each pass (20480  points covering the 2000 Mhz.). The median fit has been subtracted from each fit.
•   Plotting tsysall  with the new cal values (.pdf)  Tsys for 2005 is plotted. 1 frame for each cal type. The block plots are polA and the red plots are polB. The jump in the system temperature is when the new cals were installed.

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