Observations of Radio Sources with Flat Spectra

A study has been made of 10 radio sources which appeared from published spectral data to have straight spectra with spectral index $$\alpha \,\sim \,0\cdot 3.$$ Detailed consideration of the spectral and angular diameter data has shown that for most of the sources the spectrum is either the resultant of several components or else is self-absorbed at low frequencies. There is no definite evidence that the flat spectrum of any of the sources is due to a flat electron energy distribution. If the redshifts of quasi-stellar objects are cosmological, then the luminosity distribution of the sources agrees with that predicted from an extrapolation of the properties of sources in the 3C catalogue that includes the effects of cosmological evolution.