Lbw cal values measured 28jun12
Links to PLOTS:
to the Average CalDeflection/Tsys and Hcorcal in Kelvins
(.ps) (.pdf): .
OtherCals/Hcorcal and the fits (.ps)
Over plotting all of the cals (in
deg K) (.ps) (.pdf).
the new and old cal values (.ps) (.pdf).
measurements using 28jun12 and dec08 cals (.ps) (.pdf):
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.
The lbw cal values were measured on 28jun12. The
last measurement was on 08dec08. Some reasons why the cals were
To check this discrepancy, the cals were remeasured on 28jun12
(absorber sky) and again in 01jul12 (sky).
- the lbw stokes calibration on 27may12
showed that the cal difference polA,polB were incorrect by
15-17% (DeltaG). This error went away when the data was
reprocessed with the new cal values.
- Previous measurements of DeltaG showed:
- 09feb11,08feb11,25jan11,16jan11 deltag ok
- 23nov10: deltag off by 11%
- 30jun10: deltag ok
- TsysPolA -
TsysPolB jumped down by 3 K around 10feb12.
- Other TsysPolA-TsysPolB jumps:
- 22apr11 TsysPolA-TsysPolB jumps up by 4K.
- 28oct10 to 10dec10 TsysPolA-TsysPolB jumped down than back
up by 4K
- Both of these jumps look like they occurred after a dewar
Measuring the high correlated
cal using sky and absorber: (top)
The high correlated cal value (diode 1
going to polA and polB) for lband wide was measured on 28jun12
using the mock
These observations used the mock spectrometer with the
hardware winking cal (the faa radar blanker was not used).sky
starting at 16:00 There were heavy clouds and lightning in the
distance (but no local rain). The FAA blanker was not used..
- absorber measurement: morning of 28jun12
- on Sky measurements:
- 28jun12 -16:00 heavy clouds, lightning in the distance, no
- 01jul12 - 11:00 clear, light clouds.
The temperatures used in the computation were:
||303.7K (87.1F avg temp sensor)
||from test shack feb03
The recording and processing steps were:
- The band 1120 to 1750 MHz was covered simultaneously
using 5 mock spectrometers with 172MHz, 1024 channels each.
- 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 1120 to 1750 MHz data was resampled to a fixed
spacing of (172/1024=.168MHz). This was needed since the 5
spectra were overlapped.
- A robust fit (8th order harmonic, 1st order polynomial) was
done to the ratio data (4001 points). For the sky fits, 4 points
about each excluded point were also removed.
The on sky processing for 28jun12,01jul12 were
processed separately and then averaged for the final result.
The results of the reduction are:
- Fits to the Average
CalDeflection/Tsys and HcorCal in Kelvins(.ps)
This shows the average Tcal/Tsys data with the fits over plotted
- Page 1: Tcal/Tsys plots
- The top two plots are on the absorber (polA,polB)
- The bottom two plots are on the sky. black is the 28jun12
measurement, red is the 01jul12 measurement
- The units are Tsys (about 30K for sky and 300 K for
- 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:
- The abs plots are close to this, the sky plots are about 6
- Page 2: The Hcorcal
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.
- The Trcvr curve will have the largest affect on
- 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.
- The 28jun,01jul fits were averaged.
- These are the values that will be used for the cal.
Measuring the other cals using
sky and the high correlated cal (top)
The high correlated cal was measured (see above)
using sky and absorber as the hot and cold load. The other cals were
then measured relative to the high correlated cal on 28jun12 and
again on 01jul12 (the times were right after the hcorcal
measurements). The setup was the same as the hcorcal (see above)
accept that each integration only lasted for 10 seconds (on
sky). The following cal sequence was run:
The 1120 to 1750 MHz band was measured
simultaneously. The 25 hz hardware winking cal was used. 10 scans of
10 seconds each covered all the combinations..
the recording and processing steps
- Each 10 second set was processed similar to the hcorcal above.
- The ratio (calDifX/caloffX was computed (X is each cal type)
for each 10second set and then a robust fit was done (same as
- 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.
- 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 frams has the
- 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 10 MHz
samples used for the cal lookup table.
the new and old cal values (.ps) (.pdf)..
- The solid lines are the new cals. The dash lines are the old
- Top HiCalsPolA: black Diode1 -> polA, Red
- 2nd HiCalsPolB: black Diode1->polB, Red diode2->polB
- 3rd LoCalsPolA: black Diode1 -> polA, Red
- 4th LoCalsPolB: black Diode1->polB, Red diode2->polB
- You can see that the cal values for PolA changed a lot while
the cal values for PolB remained about the same.
- The polA values changed whether polA was being fed by
diode 1 or diode2.
- This shows that the cal change was after the diode
multiplexor in the cal (postamp) chassis.
- The diode outputs did not change.
- The change was probably the connector, cable, or coupler
from cal chassis to rfi injection.
- Comparing Tsys
measurements using 28jun12 and dec08 cals (.ps)
- The plots show the tsys measurements jan12 -> 09aug12
- 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)
- PolA (black,red) differ while polB (green,blue) remain the
- 2nd frame: hcorcal (diode 1->polA, diode1 ->polB)
- The results are similar, polA changes, polB is the same.
- So the diodes did not change.
- Bottom frame (TsysPolA - TsysPolB)
- Black is Tsys for the old cals, red is tsys for the
- there was a jump down in the tsys value around 07feb12.
After that there was a slow decrease in Tsys over the year.
- If you inserted the new cals around this jump, tsys would
have remained constant (except for the slow drift)
- Stokes Calibration showed a a large error
with (CalA-CalB)/(mean(CalA+CalB)) with the old cal values
- The stokes calibration processing computes deltaG which is
the error in the the cal Difference (CalPolA -
- Calibration data was taken on 27may12 on B2209+08. It was
processed with the old cal values, and then reprocessed with
the new cal values.
- The new cal values make DeltaG close to 0.
- With the old cal values deltaG was negative. The cal
measurments showed that it was polA that was too small (not
polB being too large).