Lband (narrow and wide) SEFD, Gain, Tsys (nightime)

aug 2000 (last modified 09aug00)

       The gain, system temperature, and SEFD as a function of zenith angle were measured using correlator position switching (with cal on/offs).  The position switch was a 1 minute on, 1 minute move, 1 minute off. The cal was 10 seconds on, off.The measurements were done at night during july and august. The calibration started with lbnarrow and then switched to lbwide on 04aug00 because of troubles with lbnarrow system temperatures. The lbwide measurements were taken as circular polarization with the hybrid after the dewar inserted.

    The measurements were done at 1405, 1460, 1290, and 1370 Mhz with a bandwidth of  6.25 Mhz. The 1400 Mhz fluxes were taken from the NVSS survey.  The fluxes at frequencies  1460, 1290, and 1370 Mhz were taken from  Kuehr et al., A&AS, 45, 367, 1981 and then scaled by Nvss/Kuehr at 1400 Mhz to bring them up to the nvss epoch.  The plots have polA as a dotted line and polB as a dashed line.  They are:

  1. The SEFD (system equivalent flux density) versus zenith angle.
  2. The system temperature vs zenith angle (lbn used 1.85, 1.91 Kelvins for the cal values. lbw used the tabulated values).
  3. The gain versus zenith angle  in kelvins per Jansky using the flux from NVSS/Kuehr and tsys measured using the cal.
  4. The stability of the cals for each strip (calKelvins/(calon-caloff)). For a given strip the attenuation was not changed so the cal difference should be a constant.

Connecting the 2 data sets lbn, lbw:

    The system temperature for lbn was varying during these measurements so the sefd is not a reliable measurement. The gain relies on the flux and the cal values so it should be valid. To put the cal values for the two receivers on a common (not necessarily correct) scale, two sources were tracked on both receivers: J1037+331 and J1609+266. A 2nd order polynomial was fit to gain vs az for the common azimuths and then the ratio was computed:  lbnGain/lbwGain = .95. The daily plots of data do not have this correction made. The plot of gain vs az,za has gainlbw scaled by .95 .

Plots of the preliminary analysis   by date:

26jul00 J2035+189 (lbn)

lbn SEFD, gain, and tsys vs za            (ps)

02aug00 J1445+099, J1609+266, J1831+291, J0137+331 (lbn)

lbn SEFD,gain, and tsys vs za (ps)

  • The first source J1499+099 was done with the correlator levels set too low.
  • The dewar was warmed up and then cooled down before this run. The system temperatures (measured with cals) in polB went from 28 deg K to 35 degrees K. Since the SEFD also went from 3.7 to 5 (at 10 degrees) it was probably not the cals that changed. polA remained the same.
  • The cal scale factor for J0137+331 is changing during the strip. It may be from sidelobe leakage since this is a 16 Jy source. I need to take a closer look at the data.
  • 03aug00 J1445+099, J1640+123, J1831+291, J2035+189, J2316+040, B0116+082, J0318+164 (lbn)

    lbn SEFD, gain, and tsys vs za (ps)
  • The azimuth stopped with a triangle motion during transit of J2035+189.  On restart, the attenuator values were reset so the calscl has two separate lines for this source.
  • 04aug00 J1445+099, J1609+266 (lbw)

     lbw SEFD, gain, and tsys vs za (ps)
  • These two sources were taken in the afternoon between 17:00 and 20:00 hours.
  • This is where we switched to lbw. You can compare these two sources with there lbn values taken 02/03aug00.
  • 06aug00 J0006-000, J0129+236, J0431+206 (lbw)

     lbw SEFD, gain, and tsys vs za (ps)

    07aug00 J0040+331, J0137+331 (lbw early morning)

     lbw SEFD, gain, and tsys vs za (ps)

    07aug00 J1419+064, J1604+012 (lbn evening)

     lbn SEFD, gain, and tsys vs za (ps)


    lb gain vs az,za (ps)
        The gain was computed using the source flux and cal values for all sources (lbn and lbw) and then plotted versus azimuth and zenith angle. Each measurement is an arrow with the length proportional to the gain (1 divison = 5 K/Jy). The angle from the vertical is proportional to the gain/gainMax (for all measurements). The angle is scaled so that 180 degrees (pointing down) is 50% of the max gain. On the plot, up is north and to the left is west (azimuth location for source rising). Circles are drawn every 5 degrees in za, and rays from the center are every 30 degrees. The az,za for each point is at the base of the arrow. The lbw gain was multiplied by .95 to put it on the same scale as the lbn cals.The maximum, average, and rms gain (K/Jy) in 5 degree steps was  computed all then data and then for 5 deg za steps.
        The system temperature, sefd, and fractional polarization (actually (gaina-gainb)/(gaina+gainb) since the outputs are circular for lbn).
     gain (K/Jy) for various za ranges
    za range max avg rms
          all 9.0 7.4 .74
        0-5 9.0 8.6 .20
      5-10 8.6 7.9 .37
    10-15 8.5 7.5 .42
    15-20 8.4 6.8 .68

     lb gain vs az,za including daytime sources (ps)
    Data taken during the day in jun00, jul00 was also included in this data set. Some of these sources were tracked through midday which may account for the increased scatter.  The rotation angle is scaled to the maximum gain over the entire dataset and lbw gains are multiplied by .95 to match the lbn values.

    Scripts used to process the data:

    26jul00 : processing: x101/lb/Aug00/lbnjul00/ , plotting: x101/lb/Aug00/lbnjul00/
    02aug00 : processing: x101/lb/Aug00/lbnaug00/ , plotting: x101/lb/Aug00/lbnaug00/
    03aug00 : processing: x101/lb/Aug00/lbnaug00/ , plotting: x101/lb/Aug00/lbnaug00/
    04aug00 : processing: x101/lb/Aug00/lbwaug00/ , plotting: x101/lb/Aug00/lbwaug00/
    06aug00 : processing: x101/lb/Aug00/lbwaug00/ , plotting: x101/lb/Aug00/lbwaug00/
    07aug00 : processing: x101/lb/Aug00/lbwaug00/ , plotting: x101/lb/Aug00/lbwaug00/
    07aug00 : processing: x101/lb/Aug00/lbnaug00/ , plotting: x101/lb/Aug00/lbnaug00/
    gainAzZa: processing: x101/callb/Aug00/      , plotting: x101/callb/Aug00/,