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Дата изменения: Fri Jan 4 16:13:57 2002
Дата индексирования: Sat Dec 22 05:32:38 2007
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Поисковые слова: ngc 6520

sband narrow calibration.

23sep 2000

Description:

On/off position switching on continuum sources was done at 2380 Mhz with the sband narrow receiver  and the correlator. The setup was:
  • Pol A, pol B are native circular.
  • One minute integration's  on and then off source were followed by a 10 second cal on/off in the off source position.
  • Try to track sources rise to set.
  • Record 1 25 Mhz band centered  at RF frequency 2380 Mhz.
  • Use the total power information, cal values,  and source flux to compute tsys, gain, sefd.
  • Fit the data to a function of (az,za).
  • Compare the measured gain with the expected gain. Include losses  from pitch, roll, and focus.

    • Daily Info:

    The dates for the observations and the sources observed are:
  • 22aug00 : J2250+143, B0116+082
  • 24aug00 : J2316+040, J0129+236,J0318+164 (CTA21)
  • 26aug00 : B0116+082, J0431+206
  • 02sep00 : J1347+122
  • 03sep00 : J1330+251

    • Cal values used during calibration runs. This is a single noise diode.
    Freq [Mhz]
     cal polA [K]
    cal polB [K]
    2380
    6.76
    6.9

    Plots of combined data:  sefd,tsys,avgain, calscale, and fractional polarization

    The plots have all the data over plotted with different symbols for each source. Dotted lines are polA and dashed lines are polB.  The figures are:
    1. SEFD vs za.
    2. Tsys vs za. T
    3. Gain vs za in K/Jy.
    4. Gain (average) vs za. The average is (gainA+gainB)*.5. Since this receiver has native circular polarization, linearly polarized sources should not affect the polA, polB gains.
    5. Cal scale factor vs za. This is (cal In Kelvins)/(Cal deflection in correlator units). This should be a flat line for each run since the attenuators were not changed (within a source). Variations are probably do to gain changes in the if/lo.
    6. Fractional gain difference defined as (gaina-gainb)/(gaina+gainb).

    Plots of f(az,za):  g(az,za), tsys(az,za), g/t(az,za)

    The average gain, Tsys, and avgGain/Tsys are plotted in a 2-D plot vs az,za. Up is feed in the north and to the left is the feed in the west (when the source is rising). The length of the arrow is an absolute measure of the value. The angle the arrow makes with the vertical is a relative measure of the strength.  The rotation angle is an easy way to visualize relative strength. Be careful though since it is calculated relative to the maximum measured value. If the flux for a particular source is wrong, and it contains the maximum gain, then the angles would have a bias.
    The table at the lower left averages the value over all the dish, za 0-5, 5-10, 10-15, and 15-20 degrees. The figures are:
    1. Average gain [K/Jy]. 1 tick= 4 K/Jy. Horizontal is maximum and 180 deg (down) is 1/2 of maximum.
    2. Tsys [Kelvins]. 1 tick=10K.  Up is minimum temperature and 180 deg (down) is 2*TsysMin.
    3. Gain/Tsys [Tsys/Jy].  1 tick= .1 Tsys/Jy. up is maximum, down is 1/2 maximum.

    Fitting the data to f(az,za):

    The data is fit to:
    f(az,za)=c0 + c1*(za-10)+c2*(za-10)^2+c3*(za-10)^3+
                     c4*cos(  az)+c5*sin(  az)+c6*cos(2az)+c7*sin(2az)+
                     c8*cos(3az)+c9*sin(3az)

     Sefd-fit, Tsys-fit   These plots show the data - fit vs za for sefd and Tsys (gain is done separately below). The (za-10) terms are for za 0 through 20 degrees (unlike some of the other fits that used (za-14) for za > 14).
    1. SEFD - fit. Units are Jy/Tsys.
    2. Tsys - fit. Units are deg K.
     AvgGainbySample with fit, (data-fit) by:sample,za,az, PRFloss, and prfAzTerms.  These plots take a closer look at the average gain fit and how the azimuth terms of the fit compare to the azimuth terms of the gain loss computed from pitch,roll, and focus. The figures are:
    1. AvgGain versus sample  with the fit over plotted.
    2. AvgGain - fit by sample
    3. AvgGain - fit by za
    4. AvgGain - fit by az
    5. GainLoss  computed from pitch,roll, and focus. The gain is down by 15% at high za.
    6. Fit to avgGain. The upper coefficients are the fit to the measured data. The bottom coefficients are the gain computed from the pitch, roll, and focus errors, and then scaled to a maximum gain of 7.3 Jy (this was the measured maximum). The plots show the azimuth terms for each fit (solid measured data, dots - pitch,roll,focus).  Comparing the azimuth components should give you an idea whether the gain degradation is coming from pitch,roll, focus or from some other source (say pointing or dish irregularities). The 3 az terms line up in phase and match in amplitude. This tells us that the 3az gain loss is coming from the pitch, roll, focus and that we have parameterized the pitch, roll, focus losses correctly (at least for sband).  The 2az terms are in phase but the amplitudes differ by about 50%. The 1 az term in the data does not correspond to the 1az term in pitch roll focus.
     az components of SEFD,Tsys,Gain, and avgGain . These plots show the azimuth components (1az,2az,3az) for the sefd, tsys, gain, and average gain. . PolA is solid and polB is the dotted line. The coefficients for the fits are also printed on the plot. PolA on the top and polB on the lower portion.

    Warnings on using the fits:

    The data used for the fit does not cover the entire dish. The sources are biased for southern sources ( 6 south, 3 north) and there are no northern sources above 25 deg dec. For sources close to a dec that was included, the fit should be as good as its sigma's.  Other measurements have shown an azimuth dependence for high dec sources (>30 deg) . For these sources the gain fit should be used with caution.

    Coefficients from the fits:

    Below are listed the coefficients from the various fits. The first column in each row specifies the data that was fit. For gainAvg there is just one fit while gain,tsys,sefd have a separate fit for polA and polB.
    > last computed: Sat Sep 23 14:32:07 2000
    > fit Ids
    >  1 GainAvg
    >  2 Gain
    >  3 tsys
    >  4 sefd
     
    fId frq  c0  za-10  (za-10)^2  (za-10)^3  cosAz  sinAz  cos2Az  sin2az  cos3az  sin3az  sigma  pol calVal
    1 2380. 6.5506e+00 -6.1362e-02 -8.2047e-03  2.8626e-04  2.2321e-01  4.3514e-01  1.1014e-01 -1.6827e-01 -1.6264e-01 -6.6516e-02  2.6533e-01 a  0.00
    2 2380.  6.5933e+00 -5.7758e-02 -8.2925e-03  2.3833e-04  2.2085e-01  4.4085e-01  1.1447e-01 -1.5323e-01 -1.6536e-01 -6.3371e-02  2.6494e-01 a  6.76
    2 2380.  6.5079e+00 -6.4965e-02 -8.1169e-03  3.3419e-04  2.2557e-01  4.2942e-01  1.0581e-01 -1.8332e-01 -1.5991e-01 -6.9661e-02  2.6643e-01 b  6.90
    3 2380.  2.4741e+01 -1.4011e-02  1.4402e-02  1.9417e-03  1.1182e-02 -4.4811e-02 -6.8318e-02  1.1563e-01 -9.0259e-02 -2.7140e-02  2.0328e-01 a  6.76
    3 2380.  2.3571e+01 -1.9850e-02  1.2837e-02  2.1695e-03  5.7332e-02 -6.0762e-02 -7.3949e-02  1.4032e-01 -1.1034e-01 -6.9682e-02  2.0496e-01 b  6.90
    4 2380.  3.7527e+00  3.0317e-02  8.6473e-03  2.6441e-04 -1.3278e-01 -3.2909e-01 -1.2690e-01  1.3837e-01  1.2620e-01  4.1556e-02  2.1125e-01 a  0.00
    4 2380.  3.6219e+00  3.2557e-02 8.2619e-03  2.5050e-04 -1.2502e-01 -3.2047e-01 -1.2113e-01  1.5816e-01  1.1848e-01  3.5434e-02  2.1124e-01 b  0.00 
    processing: x101/sbn/calsep00/doit.pro
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