sband narrow calibration Sept 01

last updated 03dec01 
gain,tsys,sefd,pntErrs,beamwidth,coma,beam efficiency
Coma versus pitch and roll errors.

   Calibration runs for the sband narrow receiver were done sep01 though nov01 using the chcross routine (see aotm 99-02 sec 3.1).  Data was taken at 2380 Mhz on a few sources (about 5).  The gain was computed using the cal values (circa 2000??) and the fluxes from chris salter. Complete tracks on the standard calibrators B0134+329 (3C48) and B0518+165 (3C138) were included. Fits were then done to the gain versus azimuth and za.

    The calibration figures show:

  • Figure 1  is the gain (K/Jy)  versus zenith angle (top plot) and versus azimuth angle (bottom). B0134+329 (3C48) and B0518+165 (3C138) are the standard flux calibrators. Their gains
  • Figure 2 plots the gain versus azimuth and zenith angle. The length of the arrow is proportional to the gain (1 tick mark = 5 K/Jy). The angle of the arrow also measures the gain: vertical up is the maximum value, 90 degrees to the right is 25% of the maximum, and vertical down is 50% of the maximum value. Sources with declination < 18 deg (AO latitude) will appear on the upper half (northern part) of the dish. Sources with declination < 18 deg will appear on the lower (southern half) of the dish. Rising sources are on the left (west half of the dish) and set on the right  (east half of the dish).  The table at the bottom shows the average over the entire dish (9.48K/Jy) and the averages in 5 deg za steps.
  • Figure 3 shows the fit to the data. It is a 3rd order polynomial in za with the za^2, za^3 terms only being fit above za=14 deg. It also includes 1az,2az,3az sin and cosine terms.

  •     The top plot is (data - azfitComponents) vs za.
        The center plot is (data-zaFitcomponents-constant) vs az.
         The bottom plot is (data-fit) by source
  • Figure 4 top  is the System Equivalent Flux Density (SEFD) versus za. The units are Jy/Tsys. It shows the strength of a source needed to double the system temperature.

  • The center plot is the system temperature versus zenith angle.
    The bottom plot is the pointing error (az,za error added in quadrature) versus zenith angle.
  • Figure 5 has the beamwidth information.

  • The top figure is the average beamwidth in arcminutes versus za. The increase at high za is from spillover.
    The middle figure is the beamwidth delta defined as (avgBm+delta)/(avgBm-delta) is the ratio of the major to minor axis of the beamwidth ellipse.
    The bottom figure is the orientation angle of the majoraxis of the beamwidth ellipse. 0 degrees is along the + az direction and 90 degrees is toward positive za. The value should be 90 degrees since the za beam is larger than the az beam.
  • Figure 6 has the coma and beam efficiencies.

  • Top is the coma versus za (see atoms 2000-4 equation 3 for the definition of the coma).
    Next is the angle the coma maximum makes relative to the positive az direction (90 deg is then along the za direction). There looks like a slope with za (which wasn't there back in sep00).
    The bottom two plots are the main beam efficiency and the (mainbeam + first sidelobe) beam efficiency. Back in sep00 they were (.50,.58) . They have now increased to (.67,.76)
    CTA21 (B0316+162) and B2018+295 were not included in the gain fit.
        Although CTA21 is a good calibrator, its gain was 5-10% less than  that of 3C138 and B2041+170.  Its lower value may be because the data for it was taken on 23aug01 before the southwest adjustement of the dish had completed. The Tsys for CTA21 was also 1-2 K higher than the other sources. The distomats were not running during this period so there may have been a rain storm.
        B2018+295 looks like it has a flux that is too high (measured gain is to low). B1829+290 was also tracked and its flux gives a gain that agrees with the other sources. The flux for B2018+295 is also about 10% high when compared to the NVSS flux at 1400 Mhz.

    The idl routine gainget() can be used to evaluate the fit (see , software documentation, generic idl routines, gainget()).

    See atoms 2000-04 pages 1-4 for a definition of the beam parameters (including the coma).

    Coma versus pitch and roll errors.

         Coma is normally associated with a misalignment of the optics. The  coma  alpha parameter is used to skew the gaussian beam in a particular direction.We 've created a model of the pitch (uphill,downhill) and roll (left,right) errors of the dome alignment relative to the primary. The plot shows these errors plotted versus the coma parameter.
  • Figure 1 top plots the pitch error (black) and the roll errors (red) versus the coma parameter.
  • Figure 2 bottom plots the pitch +roll errors (combined in quadrature) versus the coma parameter.
  • The plots show a definite positive correlation between the amplitude of the coma and the magnitude of the pitch and roll errors.
    processing: x101/sbn/sep01/,,