Sbw cal values measured 26sep08
Links to PLOTS:
Plots for entire band
in Kelvins (all bands) (.ps) (.pdf)
Over plotting all cals (.ps) (.pdf)
Comparing new, old calvalues
Compare Tsys with old/new cals
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.
Comparing old, new cal values
On 18aug05 the cal cables were replaced on the sbw
receiver. Looking at the tsys measurements using the old cal values,
this caused a jump of Tsys of about 30% (lower.. so more cal was now
getting into the dewar). On 26jul06 the dewar was warmed up and then
cooled down again. This caused a jump of 10% in the system
temperature. In apr07 the dewar was shutdown for the painting project.
It was turned on at the beginning of 2008. It left warm for a large
fraction of 2008 because of the cutback in supported receivers.
Why the cals were
Measuring the high
cal using sky and absorber: (top)
The high correlated cal value (diode 1 going
polA and polB) for lband wide was measured on 26sep08 using
The sky observations tracked blank sky starting at 5 am . The sky was
absorber measurement was done around 9:00 am. In both cases
absorber) the wbw filter bank was used.
The temperatures used in the computation were:
||from test shack sep01
The sbw filterbank breaks the band up into: 1.7
to 1.88, 2.04 to 2.40, an 2.6 to 3.10 Ghz. The 100 Mhz bandwidth of
interim correlator ended up taking 5 separate measurements to cover
this range: (1700-1800,1780-1880, 2040-2140,2100-2300, and 2600-3100).
This range was covered 6 times on sky and on 6 time
on absorber. The processing wants contiguous data so the following
processing was done for each of the 5 contigous frequency sections:
- The ratio (CalOn-CalOff)/CallOff was
computed for the data.
- Each spectra covering the band of this section
(100,100,100,200,500 Mhz) was then
to an nth order harmonic and 1st order polynomial (the order was chosen
to include the ripples in the caldefl/Tsys spectra). The fit was
throwing out points whose residuals were greater than 3 sigma .
a point was excluded, 5 points adjacent to the fit were also excluded .
- A robust average of the 6 passes for each section 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
- This shows the average Tcal/Tsys data with the fits over
The top two plots are on the absorber (polA,polB) while the
two plots are on the sky. The averages were made from the 6
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
on each plot.
- The radiometer equation should give:
The absorber fits match this. The sky fits are about 6 time larger.
is because the fits are not fitting the 1 MHz standing wave from the
This is ok since that ripple should not be in the cal value anyway.
- The Hcorcal in kelvins
- The first two plots show the cal fits in kelvins measured from
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
- 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 Calsky.
- The bottom plot is the cal In kelvins from the Y factor. The *
every 10 MHz. PolA is black and polB is red. These are the values that
will be used for the cal.
- Hcorcal in kelvins (all bands):
- This shows the hcorcal for polA (black) and polB (red) for the
entire bandpass. The fit to the averages has been evaluated every 20
Mhz. The spaces are where no data was taken.
- The green, blue lines are receiver temperatures for polA,polb.
The first set of plots show the
for each pass through the data. The second set over plots the fits to
pass to see how stable the system is.
- CalDeflection/Tsys for each pass.
- The first page shows on absorber for the 9 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
about 300K). The dashed vertical line shows the start of each 100 MHz
(4sbc*25MHz each). Very little of the rfi is coming through the
- The second page shows on the sky for the 9 passes
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
were taken separately). The birdie around 1240/1260 are the punta
salinas radar. The below 1400 MHz looks like our old resonance ?
- Fits to the CalDeflection/Tsys
for the each pass.
- 9 passes thru the frequency band.
This over plots the fits to each pass (6144 points covering the
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.
Measuring the other
cals using sky and the high correlated cal (top)
The high correlated cal was measured (see above)
sky and absorber as the hot and cold load. The other cals were then
relative to the high correlated cal on 26sep08 starting around 5:00am.
sky was tracked, the filter bank was used,
and the following cal sequence was run:
100 MHz at a time was measured (4 by 25MHz) going
1700 to 3100MHz (in the 5 frequency sections). The cal was cycled
on/off for 3 secs at each
The entire frequency range was repeated 4 times.
The ratio (calOnX-calOffX)/caloffX was computed
(X is the other cals) and then it was divided by
A spectrum for the entire pass was then constructed of the other cals
to the hcorcal. The spectral fits for the 4 passes were averaged. The
spectra was multiplied by the hcorCal value in kelvins (this
the hcorCal shape). The resulting spectra was fit with an nth order
and 1st order polynomial. For more info see
computing the cal value.
The results of the reduction are:
- The average calValues in kelvins
and the fits.
- The fits to the 4 passes have been averaged together and then
by the hcorcal fit (in kelvins). There are 14 plots. 7 cals each with
and polB. The red lines are the fits to the data.
- Over plotting all of the cals
(in deg K).
- The top plot is the high cals and the bottom plot is the low
solid lines are polA while the dashed lines are polB.
for the 4 passes.
- There is 1 page for each calType (7 pages).
- The top plot is polA and
bottom plot is polB. T
- The 4 passes through the freq range are over
with an offset. The units for the y axis are TcalHcorcal since each of
the cal deflections have been divided by the hcorcal deflection.
- Fits to the
CalDeflX/calHcorcalDefl for the 4 passes.
This over plots the fits to each pass showing any variations in the
fits by pass
Compare old,new cal values
The first plot compares the new and old cal
(.ps) (.pdf) :
The second plot compares Tsys measured at 2290
for 27jul08 to 25sep08 (.ps) (.pdf):
- Solid lines are the new cals
- Dashed lines are the old cal values (2004)
- The black lines are diode 1
- the red lines are diode 2.
- The cal values have increased. This will increase the Tsys
(relative to using the old cal values).
- Tsys has gone from 24 K to about 34K. The old cal values were too
- The spread in Tsys for different cals is much smaller for the new