A well defined sample of 72 Gigahertz Peaked Spectrum radio sources is
compiled, having turnover frequencies in the range of 0.5 - 10 GHz. U
sing this sample, the canonical GPS radio spectrum is constructed, whi
ch is found to have a constant shape, independent of AGN type, redshif
t or radio luminosity. A possible deficiency of low turnover frequenci
es at high redshift is found, which may reflect a physical mechanism w
here turnover frequency and radio luminosity are correlated.