Lbw cal values measured 28apr16
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 28apr16 and jun12 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 28apr16.
- The last measurement was on 28jun12.So it's long over due.
- Tsys had been increasing for lbw.
- We've also seen an increase in the sefd for lbw.. so it's
probably not just the cal values changing.. but to debug this
problem, having the correct cal values will help.
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 28apr16
using the mock
These observations used the mock spectrometer with the
hardware winking cal (the faa radar blanker was not used). The sky
was clear for the on sky measurements.
- absorber measurement: morning of 28apr16 09:38
- on Sky measurements: morning 28apr16. 10:41 to 10:45
The temperatures used in the computation were:
||300K (80.5F 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
- there was one pass through the band for absorber, and 1 pass
through the band for on sky.
- 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 results of the reduction are:
- Fits to the Average
CalDeflection/Tsys and HcorCal in Kelvins(.ps)
(.pdf): This shows the
average Tcal/Tsys data with the fits over plotted in red.
- Page 1: Tcal/Tsys plots
- The top two plots are on the absorber (polA,polB)
- The bottom two plots are on the sky.
- 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 within a factor of two of
this.. close to this, the sky plots are about 6 times
- Page 2: The Hcorcal
- 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 while computing
calSky. (measured way back in 2003).
- 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.
- These are the values that will be used for the high
- The cal values measured using Absorber and Y ratio has
always been a bit different than the value measured using just
- The difference seen in apr16 is larger than that computed
back in jun12.
- The difference can come from the value of Tscattered
- The new polA difference shows a stronger Frequency
dependence that polB (and the jun12) values.
- The Treceiver value that i am using comes from ganesh and
lisa's measurements on the antenna test range back in 2003.
There was another measurement made in 2007 but ganesh never gave
me the values..
- Since we've seen an increase in the SEFD of lbw over the last
few years (
SEFD changes jan2006 through jun2016), it might be a good
idea to remeasure the lbw receiver temperature to see whether it
has changed or not (especially since we have inserted a
new foam window after the old one failed back in may15.
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 (on sky) relative to the high correlated cal on
28apr16 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 into 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
- the gap with no data is the platform painting project.
- 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
- The cal values for PolA and polB have decreased
by about 20% since the 2012 measurements.
- This is probably from a change in attenuation between the
diode and the dewar (or I guess the diodes them selves
could have changed.
- Comparing Tsys
measurements using 28apr16 and jun12 cals (.ps)
- The plots show the tsys measurements jan16 -> jul16
- 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) and polB (green,blue) have both
- 2nd frame: hcorcal (diode 1->polA, diode1 ->polB)
- The results are the same.
- Bottom frame (TsysPolA - TsysPolB).
- Black is TsysDif for the old cals, red is tsysDif
for the new cals.
- The receiver was brought down to the lab for maintenance
during the painting shutdown.
- when the receiver was reinstalled in apr16, tsysA-TsysB
decreased by about 5K.