cband hi (6 to 8 ghz) calibration

feb04

     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.


Sections:

History
Recent system performance measurements
Daily monitoring of Tsys
Dewar temperatures
Calibration measurements
All measurements in date order


History:



Calibration measurements:

19sep12: new cal values measured 28jun12.
29feb04: fit Gain Curves to feb04 calib data.
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 performance.


All measurements in date order

19sep12: new cal values measured 28jun12.
08aug05: check system performance for Thankins.
18may04: aas plots for jagadheep
29feb04: fit Gain Curves to feb04 calib data.
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 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???).
processing: x101/050808/doit.pro


feb04.  fit GAIN CURVES to calib data.  (top)

link to gain curve plot
link to system performance for the data used to fit.

    Gain curves were fit to the cband hi gain data taken during feb04..The plots show the gain data (black) and the fits (red) for 6600, 6900, 7200, and 7400 Mhz.

Plots of the system performance  (gain,tsys, sefd, beamwidth,...)  for this dataset is also available.

    The routine gainget() or corhgainget() will now return the cband hi gain for data after 14feb05 (horn installation).
The coefficients can be found in the ascii file  data/gain.datR10 (this is provided in the AO idl distribution for correlator
routines). You can also find a copy of it at AO in /home/phil/idl/data/gain.datR10.

processing: x101/cbh/feb04/dogainfit.pro


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  show the masers. 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.
    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).
 
processing:x101/040220/cbh.pro


15feb04: tsys vs frequency.    (top)

    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.
processing: x101/040215/cmptsys.pro


15feb04: on/off position  switching on 3C454.3 covering the entire band (shows resonances)   (top)

    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 plotted).
    The 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 correct order).
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.
processing: x101/040215/onoff3c454.3_15feb04.pro


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 sources.         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.
processing: x101/040215/doit.pro


15feb04: RFI: rms/mean vs frequency  for 60 second blank sky.   (top)

 plots of the rms/mean for the entire band.
plots 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).

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.
 
processing:x101/040215/onoff3c454.3_15feb04.pro
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