| Abstract | Accurate values of the flux density are given for nearly all sources in the Revised Third Cambridge Catalogue at frequencies of 38, 178, 750, 1400, 2695, and 5000 MHz. These have been used to determine the spectrum of each source over this frequency range. It is concluded that the form of the spectra in many sources is determined not only by the energy distribution of relativistic electrons but also, as a result of self-absorption, by their spatial distribution. Sources identified with quasi-stellar objects have a wider dispersion of spectral indices than those identified with radio galaxies, particularly at the higher fre- quencies. Among the radio galaxies, the intrinsically strongest sources appear to have the steepest spectra. Unidentified sources have steep spectra similar to those of the stronger radio galaxies, and they are probably distant galaxies |
