cband cal values measured 06jul06
Links to PLOTS:
to the Average CalDeflection/Tsys (.pdf)
in kelvins (.pdf)
for the 10 passes (.pdf)
to the CalDeflection/Tsys for the 10 passes (.pdf)
average calValues in kelvins and the fits (.pdf)
plotting all of the cals (in deg K) (.pdf)
for the 2 passes (.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.
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.
The high correlated cal value (diode 1 going to
polA and polB) for cband was measured 06jul06 (on absorber) and sky
using the sky/absorber
technique. The observations used 3 second calon followed by 3
second cal off. For the sky observations, blank sky was tracked.
Measuring the high correlated
cal using sky and absorber: (top)
The temperatures used in the computation were:
||from rcvr test shack
The band 4000 to 6000 MHz was covered 10 times on
absorber and sky. The ratio (CalOn-CalOff)/CallOff was then computed for
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:
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
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.
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.
The first set of plots show the calOn-caloff/caloff
for each pass through the data. The second set over plots the fits to each
pass to see how stable the system is.
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).
to the CalDeflection/Tsys for the 10 passes (.pdf) : This over plots
the fits to each pass (20480 points covering the 2000 Mhz.).
The high correlated cal was measured above using sky
and absorber as the hot and cold load. The other cals were then measured
on 12jul06 relative to the high correlated cal. Blank sky was tracked and
the following cal sequence was run:
Measuring the other
cals using sky and the high correlated cal (top)
100 Mhz at a time was measured (4 by 25Mhz) going from
4000 to 6000 Mhz. The cal was cycled on/off for 3 secs at each step.
The entire frequency range was repeated 2 times. The sbc polA drop was
not longer present when this data was taken.
The ratio (calOnX-calOffX)/caloffX was computed
(X is the other cals) and then it was divided by (calOnHcor-calOffHcor)/calOffHcor).
A spectrum for the entire pass was then constructed of the other cals relative
to the hcorcal. The spectra for the 2 passes were averaged. The average
spectra was multiplied by the hcorCal value in kelvins (this removed the
hcorCal shape). The resulting spectra was fit with an 23th order harmonic
and 1st order polynomial. Some of the 100 Mhz sections that had small jumps
were not used in the averaging or fitting. For more info see
computing the cal value.
The results of the reduction are:
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.
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).
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