cband cal values measured 06jul06

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.

---

Why the cals were remeasured.

• 02feb06: Tsys Pol jumped from 24.2 to 30.6 K.
• 25May06: A loose sma connector was found on the cal PolA cable. After tightening the cable, the Tsys value for PolA went from around 30K to  16.8 K. The amount of cal getting into the receiver was now different than the pre 02feb06 value.

---

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

    The temperatures used in the computation were:
 

Tabsorber	300.3 K
Tsky	3 K
Treceiver	from rcvr test shack
Tscattered	15 K

    The band 4000 to 6000 MHz was covered 10 times on absorber and sky. The ratio (CalOn-CalOff)/CallOff was then computed for the data.
    After analyzing the data a problem was found in polA sbc 4 of each 100 Mhz measurement. The calDeflection/Tsys was smaller for this 25 Mhz than the other 3 (sbc1 thru 3). This problem was not seen in the alfa data so it must have been in the interim correlator or the cable that went from the interim correlator ot the if/lo. To get around this, the 25 Mhz of sbc 4 were not used in the fit. This change the harmonic fit from a 23rd order to a 12th order (so the fit was not influenced too much the the missing 25 Mhz data).
    Each spectra of 2000 Mhz (20480 points) was then fit to an 12th order harmonic and 1st order polynomial. 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  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) :  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.  There are 10 passes through the frequency range that were averaged..  The units are Tsys (about 25K for sky and 300 K for absorber). You cans see the dropouts in Tcal/Tsys every 25 Mhz. This was the polA sbc4 problem. This data was not used in the fit. 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*10loops*2hanning)=.0006
The absorber fits are close to this. The sky fits are about 10 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) :
• 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 10 passes (.pdf)  :
• The first page shows on absorber for the 10 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 dropouts every 25 Mhz are caused by the sbc4 problem.
• The second age shows on the sky  for the 10 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 10 passes (.pdf) : This over plots  the fits to each pass (20480 points covering the 2000 Mhz.).

---

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 averaged fits (.pdf) :  The data for the 2 passes have been averaged together and then multiplied by the hcorcal fit (in kelvins). The 2 fits for each cal were also averaged and plotted. There are 14 plots. 7 cals each with polA and polB. The red lines are the averaged 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)  .  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).

• CalDeflectionCalX/calDeflectionHcorcal for the 2 passes (.pdf) . There is 1 page for each calType (7 pages). The top plot is polA and the bottom plot is polB. The 2 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.  There are a few 100 Mhz sections were the cal/Tsys jumps (100 Mhz of data was taken at a time). Either the cal amount changed during these integrations, or something was zapping the receiver causing Tsys to change. Since the entire 100 Mhz jumped together, it was not something after the downstairs mixers (which split up into 4 25 Mhz bands).

home_~phil