Measuring the sband high cal values.
09mar04
Links to sections:
Measuring the hcorcal
Measuring the ratio of the other
cals to the hcorcal
checking the cal values
Links to plots:
The hcorcal
measured values:
The
spectra of (calon/caloff -1).
The
power levels during the measurements.
The
ratio of the other cals to the hcorcal:
Tsys
for 2004 using old and new cals
The sbh diodes were replaced on 13feb04. On 9mar04 the
diodes were calibrated using the sky and absorber. The correlator was configured
as 25 Mhz by 256 lags by 4 sbc. 3000 to 4000 MHz was
covered in 100 Mhz chunks (10 steps). At each step a 3 second integration
with the hcorcal on was followed by a 3 second integration with the cal
off. The frequency range 3000 to 4000 was covered 6 times on absorber
and 6 times on the sky. After this the "other cals" were measured
relative to the hcorcal while tracking blank sky. See
measuring cals on the telescope using sky and absorber for a more detailed
description.
Measuring the hcorcal:
(..top)
The temperatures used for sbh were:
Temperatures Used
| Trcvr |
from hilltop measurements |
11 to 18K |
| Tabs |
absorber temperature |
301 K |
| Tsky |
sky + scattered ground radiation |
3 + 13=16K |
This shows the results of the measurements.
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Fig 1 plots the cal Values measured the 3 different ways:
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Black shows cal polA, polB measured relative to the absorber.
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Red shows cal polA,polB measured relative to the sky using Trcvr from the
hilltop measurements.
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Blue is cal polA, polb measured using the ratios of the cals with absorber
and sky.
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Fig 2 fits a 12th order polynomial to the cal value. The top plot is polA,
the bottom plot is polB
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Green are the data values used for the final fit
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Black are values gt 2 sig from the original fit.
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Fig 3 plots the cal values vs freq for polA averaged over the 25 Mhz bandwidths.
The color are the 6 separate measurements. Top to bottom is the cal measured
using: the absorber, the sky, and the sky absorber ratio.
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Fig 4 polB version of fig 3.
The spectra for the cal (calOn/caloff -1)
for the data taken on the sky is shown in the plots. Each color is a different
pass through the frequency range 3000 to 4000 Mhz (6 in total). Offsets
have been added to each pass for plotting purposes. The top plot is polA,
the bottom plot is polB.
The power levels during the measurements are shown.
Black is pola and red is polB.
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Fig 1. Top the power level measured at the fiber optic transmitter (the
actual power is +20db more since a 20db coupler is used).
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Fig 1.Bottom the power at the downstairs power meter (actual power is +10
db more).
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Fig 2. The 0 Lag power (25 Mhz) normalized to the median value for all
of the measurements. The figures are sbc1 thru 4. The large variation at
the beginnning is on the sky (where the cal value is a large
fraction of tsys). The last part is on the absorber.
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Fig 3. The same as figure 2, but the power counter data (50 Mhz that goes
to the digitizer).
The absorber and sky/absorber ratio give consistent
results. They were used to compute the cal values. The variation in Calsky
comes from the value of Trcvr used. The error in Trcvr is a small fract
of Tabs and it is divided out using the Y factor, so these two agree. The
error in Trcvr is a larger fraction of Tsky and causes calSky to jump around.
processing: x101/040309/hcorcal/sbhcal.pro
Measuring the
ratio of the "other" cals to the hcorcal. (..top)
On the same day (09mar04) blank sky was tracked with
the sbh receiver. A sequence of 10 cal on/off measurements were done using
the correlator configured as 25 MHz x 4 boards. The sequence was (hcorcal,
hcal, hxcal, h90cal, hcorcal, lcorcal, lcal, lxcal, l90cal, hcorcal). This
sequence was repeated covering 3000 to 4000 Mhz. The hcorcal was measured
using the sky and absorber (see above). The ratio of the "other" cals was
then computed relative to the hcorcal (see
measuring cals on the telescope using sky and absorber ).
For each cal at each frequency step, the cal on/off
spectra was computed and then cumfiltered over the 25 MHz frequency and
the 3 repeated loops to remove any "obvious" rfi. The ratio with the hcorcal
was then computed by interpolating between the 3 hcorcal measurements.
The interpolation was used since each cal is measured relative to
the calOff (or tsys) and tsys varies as we track blank sky.
The
ratio of the other cals to the hcorcal is shown in the plots:
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Fig 1 top shows the high cals measured relative to tsys versus frequency.
The * are pol B. The vertical lines show the 100 Mhz steps. There were
4 25 Mhz measurements at each frequency setting. Some of the cal sizes
track each other since they come from the same diode (e.g.. polA hcorcal:hcal,
hxcal:h90cal, polB hcorcal,h90cal). The bottom plot has the low cals. The
bump at 3200 Mhz and at 3600Mhz is seen to be only in diode 1.
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Fig 2 top plots the ratio of the cal/hcorcal for the high cals. The horizontal
red, black line have diode1->polA and diode 1->polB. This is the same configuration
for the hcorcal so the ratio is close to 1. The red (bright,dark)
lines have diode2->polB through the 90 deg leg of a hybrid while the green
violet lines have diode 2 -> polA through the 0 deg leg of a hybrid.
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Fig 2 bottom is the ratio of the low cals to the hcorcal. The non
zero slope for the ratio of diode1->polAL / diode1->polAH is probably the
frequency response of the 10db coupler used to create the low cal.
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Fig 3 show how the hcorcal measurement varied for the 3 hcorcal samples
taken at each frequency. The 2nd (red) and 3rd (green) hcorcal measurement
were divided by the first hcorcal measurement (and then subtracted 1).
These values stay within .5%.
The ripple in the cal value that has a peak at 3200 Mhz and 3600 Mhz is
coming from diode 1. It is before the switch in the postamp box that selects
diode 1 or diode 2 to be sent to a particular polarization. It may be a
bad match back at the diode.
processing: x101/040309/othercals/sbhcal.pro
Checking the cal
values (..top)
The tsys measurements for 2004 were recomputed using
the new cal value at 3500 Mhz. The plot shows the Tsys
values for 2004 using the may03 cal values (top) and the mar04 values
(bottom).
processing:x101/040309/othercals/chksbhcal.pro
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