Lband wide SEFD, Gain, Tsys by Frequency (daytime)

14july00

    The SEFD (System Equivalent Flux Density), gain, and system temperature were measured at various frequencies using the lband wide (lbw) receiver on 14jul00 during the day.  One minute on/off position switching followed by a 10 second cal were done using the correlator and a 3.125 Mhz bandwidth. The correlator was configured to take four separate frequencies simultaneously. Two sets of four frequencies were defined and the correlator switched between the two sets every 3 minutes.

The frequencies used were:

  • SET  1: 1175, 1279, 1375, 1405 Mhz
  • SET  2: 1405, 1515, 1650, 1712 Mhz

    • These particular frequencies were chosen to avoid nearby interference.

    The sources used were:

  • J0521+166 (3 points)
  • J0840+132 (20 points)
  • J1120+143 (20 points)

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    The plots (of polA only) can be found at:
     Sefd, tsys, gain by sample (ps)
     Sefd, tsys, gain showing ratio of freq/1405 Mhz (ps)
     Sefd, tsys, gain by azimuth (ps)
     Sefd, tsys, gain by zenith angle (ps)
    In the plots, each frequency has a different symbol. Each source has a different line style.

    Computing the plots:

    When computing the system temperature, the tabulated cal values were averaged for polA and polB since the data was taken in circular polarization mode ( the hybrid after the dewar combined the two linears to give circular).

    The flux and its frequency dependence  was computed using the formulas from Kuehr et al., A&AS, 45, 367 (1981). Since at least one of the sources is variable (J0521+166) ,  all of the fluxes were  scaled by the ratio of the NVSS 1400 flux/KuehrFluxAt1400. This assumes  there is no frequency dependence in the time variability.

    Comments

    Looking at Tsys vs za, 1175 Mhz is the highest Tsys while 1650 Mhz is the lowest. All the other frequencies group pretty much together. It's not obvious whether the Tsys is bad or the cal values are not well known at the outlying frequencies.  If the gain was constant then you would expect the SEFD of 1175 Mhz to be the worst (largest) while 1650 Mhz would be the best (lowest). The SEFD measurement has 1650 the worst sefd and 1175 somewhere in the middle so either the gain is not constant or the cal values for at least 1650 are bad. 
    processing: x101/lb/Aug00/lbwjul00/lbwfrqhop.pro
    plotting  : x101/lb/Aug00/lbwjul00/lbwfrqhop{az,za,ratio,()}plt.pro
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