Lbw 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.

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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	300 K
Tsky	5 K
Treceiver	from test shack feb03
Tscattered	15 K

    The band 1120 to 1720 Mhz was covered 10 times on absorber and 10 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 problem was found in the cal values measured using the 25 Mhz bandwidth of sbc4. The cal/Tsys ratio came out low for all 25 Mhz bands that this sbc measured. The 25 Mhz sections from sbc 4 were not included in the fits.

    A robust average of the  10 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 10 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 7 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. You can also see that the radar 1240/1260 still gets in through even on the absorber.
The 25 Mhz drops every 100 Mhz in polA are being caused by the sbc 4 problem. This problem went away on 08jul06.
• 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 not so close. The calsky can be shifted up or down by changing the amount of Tscattered. The Trcvr curve will also affect  Calsky the most.
• 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 10 passes thru the frequency band (.ps)  (.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 it is about 300K). The dashed vertical line shows the start of each 100 Mhz integration (4sbc*25Mhz each). For polA the dropouts are occurring for sbc 4.  This problem must be coming at or after the 2nd mixer (750 to 260). It does not show up in the alfa data so it is probably not the output buffer amplifiers. The 1240/1255 birdies that are coming through are from the aerostat radar.
• The second page 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 30K on the sky). The dashed lines show the 100 Mhz boundaries (that were taken separately).  The sbc 4 jumps are also present.
• Fits to the CalDeflection/Tsys for the 10 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. The 1220 to 1320 band (especially on the sky) varies for polA and polB. This is being caused by the aerostat radar at 1240/1260.

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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 7 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. The only problems appear around the 1250-1290 where the radars occur.

 
• 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).

• CalDeflectionCalX/calDeflectionHcorcal for the 7 passes (.ps)  (.pdf). There is 1 page for each calType (7 pages). The top plot is polA and the bottom plot is polB. The 7 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. The 25 Mhz band from 1270-1295 is bouncing around a lot (this is sbc 3 not sbc4). It may be that the digitizer (which looks at a 50 Mhz bandwidth) is getting compressed by the radar at 1260).
• Fits to the CalDeflX/calHcorcalDefl for the 7 passes (.ps) (.pdf). This over plots  the fits to each pass (6144 points covering the 600 Mhz.). There is lots of variation (especially in the low cals) around the aerostat radars (1240/1260).
• 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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