I study active galactic nuclei (AGN) at various frequencies from radio to the TeV domain. By performing multifrequency observations of both bright blazar-type and fainter low-luminosity sources such as narrow-line Seyfert 1 galaxies, I aim to examine the evolution of AGN and the triggering of relativistic jets in them. My main interest is radio astronomy and the observations we perform with the 14-m Metsähovi Radio Observatory antenna at high radio frequencies.