Absolute calibration of a wideband antenna and spectrometer for sky   noise spectral index measurements
  A new method of absolute calibration of sky noise temperature using a three-position switched spectrometer, measurements of antenna and low noise amplifier impedance with a vector network analyzer, and ancillary measurements of the amplifier noise waves is described. The details of the method and its application to accurate wideband measurements of the spectral index of the sky noise are described and compared with other methods. 
Alan E. E. Rogers, Judd D. Bowman
astro-ph.IM