cband hi (6 to 8 ghz) calibration
The cband hi receiver covers 5.9 to
8.1 Ghz (maybe a little more on the edges). It is a dual beam
receiver but only one of the beams is currently installed. cbh or
cbh_1 refers to the first (currently installed horn/amp). cbh_2 is
the 2nd horn/amp.
All measurements in date order
- 160428: while remeasuring cals, found loose cal cable into
dewar. Tightened cable during cal measurement.
- 14feb04 surveyed horn into position.
- 11feb04 installed in dome.
19sep12: new cal values measured
29feb04: fit Gain Curves to feb04 calib
20feb04: looking at 6.7 Ghz
masers: IRAS srcs: 19410+2336, 20110+331
16feb04: Tsys vs frequency
15feb04: on/off position switching on
3C454.3 covering the entire band (shows resonances)
15feb04: first look at the cband hi
new cal values measured 28jun12.
measurements in date order
08aug05: check system performance for
plots for jagadheep
fit Gain Curves to feb04 calib data.
looking at 6.7 Ghz masers: IRAS srcs: 19410+2336, 20110+331
Tsys vs frequency
15feb04: on/off position
switching on 3C454.3 covering the entire band (shows resonances)
first look at the cband hi performance.
15feb04: RFI: rms/mean vs frequency
for 60 second blank sky.
08aug05 check system performance
for Thankins. (top)
Tim hankins had been looking at giant pulses from
the crab with cbandhi (as well as cb,xb,sbh..). He had not seen any
pulses for a few days and asked us to check the system performance.
A calibration run was done on 08aug05 using B1622+238 (3C336) .62 Jy
at 7000 MHz and B1829+290 .91 Jy at 7000 Mhz. The calibration runs
make measurements at 6600, 6900, 7200, and 7400 Mhz The plots show the
measured system performance (.ps) (.pdf):
The system performance and gain do not look like they should be
causing problems with the cband high measurements. Tim's lack of
pulses must have been some other problem (un-cooperative pulsar???).
- Page 1: plotted vs za is: gain, tsys, SEFD, and average beam
width. The source B1622+238 is extended (~24 asecs) so its
gain/sefd/beamwidth should be worse.
- Page 2: This is the pointing error in za (top two plots) and
azimuth (bottom 2 plots). The source B1645+174 is included. It
was taken on 05aug05 using sband high (3-4 GHz).
feb04. fit GAIN CURVES
to calib data. (top)
to gain curve plot
system performance for the data used to fit.
Gain curves were fit to the cband hi gain data
taken during feb04..The plots
the gain data (black) and the fits (red) for 6600, 6900,
7200, and 7400 Mhz.
the system performance (gain,tsys, sefd,
beamwidth,...) for this dataset is also available.
- Fig 1 shows the az,za distribution for the data. The fit used
a 3rd order polynomial in (za-10) and 1az, 2az, and 3az sin, cos
- Fig 2 plots the gain data and the fit to za. The fit
equation is plotted with the sigma for the fit (in K/Jy).
- Fig 3 plots the fit residuals (data-fit) vs za.
The routine gainget() or corhgainget() will
now return the cband hi gain for data after 14feb05 (horn
The coefficients can be found in the ascii file
data/gain.datR10 (this is provided in the AO idl distribution for
routines). You can also find a copy of it at AO in
20feb04: looking at 6.7
Ghz masers: IRAS srcs: 19410+2336, 20110+331
Two masers were tracked on 20feb04 with the cband
hi receiver. The correlator was set to: .781 Mhz with 2048 channels,
and .3905 Mhz with 2048 channels. This gave frequency resolutions of
.034 km/sec and .017 km/sec (after hanning smoothing). The plots
The receiver saw the two masers. The noise levels measured were
close to the expected values. The source flux is not known since
there is not yet a gain curve. It also turns out that the individual
components from these masers tends to be variable.
- Fig 1 was a 60 second on, off position switching. The plot is
in degrees K. There has been no gain correction (since we do not
yet have a model ).The bottom figure is a blowup showing the
baseline. The rms noise is what is expected.
- Fig 2 is IRAS source 20110+221. There were 9 60 second ons
each followed by a cal on, off. Each scan was scaled to kelvins
and then a linear baseline was removed (there was no bandpass
correction). The top two plots are the wider resolution (.034
km/sec). The bottom two plots are the higher resolution (.017
km/sec). There is a birdie in the center of the band that comes
from the correlator digital filters. The measured rms's are a
bit higher than the expected. This is probably do to
contamination from the source, and the fact that this was not a
position switched measurement so the bandpass was no divided
out. Since no off position was taken, there is no information
about the continuum from the source.
You can see previous measurements of these
sources in A
survey of the 6.7 Ghz methanol maser emission from IRAS sources
(M. Szymcazk. Astron.Astrophys. Suppl. Ser. 143,269-301).
15feb04: tsys vs
On 15feb04 on off position switching was done on
the source 3C454.3. The correlator was setup for 4 by 50Mhz bands.
60 1 second records were taken at the on and then the off position.
The cal was then fired after the off. The band from 5750 through
8150 was covered two complete times.
The cal on, off was used to compute the system
temperature. 10 percent of the bandpass along the edges as well as
any outliers were not used in the computation. The average Tsys was
then computed for each of the 50Mhz bands. The plot
shows Tsys vs frequency.
The resonance at 5845 and 7336 cause Tsys polA to increase. Part of
this will be a true Tsys increase while part will be an error in the
measurement of the cal values at these frequencies (since they were
injected after the omt and did not go through the resonance). Tsys
for polB jumps around a lot more than pola fore freq less than 7200
Mhz. This same pol is the one that has a large number of resonances
in the region below 7200 Mhz.
- Tsys PolA is black.
- Tsys polB is red.
- The green line is pola (srcOn-off)/off for 3C454.3. It has
been scaled and offset for plotting. It shows where the
resonances in the feed occurs.
- The blue line is polB (srcOn-off)/off for 3C454.3.
15feb04: on/off position
switching on 3C454.3 covering the entire band (shows resonances)
On off position switching was done on the
continuum source 3C454.3. The correlator was setup to do 4 50 Mhz
frequency junks simultaneously. A one minute on,off was done and
then the frequency band was moved up by 200 Mhz. The frequency range
5750 through 8150 Mhz was sampled two complete times. The first pass
covered za 15 through 5 degrees za. The second pass covered
the za range 3 degrees rising to 10 degrees setting.
(ON-OFF)/OFF was computed for each pair. The data
is plotted in units of Tsys with the full frequency resolution
(24Khz but 100 channels on each each of a 50Mhz band is not
plots shows the source strength in units of Tsys vs frequency.
The omt has a Y with polB going off at the
angle and pol A going straight thru (at least i think this is the
- Pol A is in black and polB is in purple. There are two
complete traces for each pol since there were two complete
- The green horizontal lines are the boundaries of each 50Mhz
- The red vertical lines are spaced by 200 Mhz. Data between
these lines was taken at the same time.
- The jumps in power levels for each 200 Mhz integration is
probably from the pointing.
- There are two large resonances at 5840 Mhz and 7330 Mhz. The
are negative going since the resonance in the on is negative
going while the resonance in the off is positive going.
- The ripples in polB cover most of the band. The ripples
in polA start after the 2nd resonance and then follow what pol B
The positive going resonances in the off were a bit of a surprise at
first. If the omt is cooled to 20 kelvins, then it should have close
to the same temperature as the sky radiation. In this case you
should not see much of a bump. This is what happens with our other
cooled mts. On the other hand, there is a thermal transition with a
long 50 K stage, and then another transition to the 300 K. If the
trapped mode is reflecting back toward these higher temperature
areas, then you would probably expect a bump in the resonance while
on the sky.
We need to put an absorber in front of the horn
and do this same experiment. It will give us a cleaner picture of
what is going on without any jumping around because of the pointing.
15feb04: first look at the
cbhi performance. (top)
Calibration scans were done on 4 sources on
14feb04 (after the horn survey) and 15feb04. Data was taken
during the daytime (13:00 hours to 15:00 hours). The
frequencies measured were: 6600, 6900, 7200, and 7400 Mhz. The
source J2253+161 (3C454.3) was used just for the pointing offsets
since it is a variable source. The plots
show the system performance. The plotted parameter is the
average of polA and polB (stokes I/2). The cal values measured on
the hilltop test range were used in the calibration. Color is used
to separate the frequency measurements while symbols separate the
The gain (which depends
on the validity of the cals and the source fluxes) varies from 2.5
to 7.5 K/Jy for the frequencies measured. The source B0134+329
(3C48) has the largest gain (and also the best known flux).
The sefd goes from 4 to 8 Jy/Tsys. The Tsys measurement is the
average of polA and polB.
- Fig 1 has the gain (K/Jy), Tsys (degK), Sefd (Jy/Tsys), and
beam width (asecs).
- Fig 2 plots the coma parameter, first sidelobe height,
main beam efficiency, and the main beam plus first sidelobe.
- Fig 3 has the zenith angle pointing error (vs za and azimuth
) followed by the azimuth pointing error (vs za and azimuth).
- Fig 4 shows the az,za coverage of these sources on the dish.
15feb04: RFI: rms/mean vs
frequency for 60 second blank sky. (top)
the rms/mean for the entire band.
of the spectral density function for the bands with rfi.
On 15feb04 60 second on/off position switching
was done on 3C454.3. The off position scans were used search for
rfi in the band. For each off position the rms/mean was computed
by frequency channel for the 60 one second integrations. This was
then plotted versus frequency. The correlator was setup to cover
200 Mhz in 4 50Mhz bands using 3 level sampling. It took 12
integrations to cover the entire 2.4 Ghz band. The entire band was
measured 2 times. The
plots show the rms/mean for the entire band.
Frequencies with large rms/Mean are rfi (since it is usually not
stationary in time).
- PolA is black, polB is purple.
- The green lines are the edges of the 50 Mhz bands
- The red lines are the 200 Mhz integrations that were done at
The second plot shows the
spectral density function for the bands with rfi.
Note: This data was taken from 12:45 to 14:00 AST .
Some of the rfi could be reflections from the sun.
- The plot is a peak hold on each channel for the 60 seconds.
- There are two complete passes through the band. The second
pass had the frequencies offset by 5 Mhz from the first pass.