Observations of fine structure in very weak radio sources

A study of sources from the 5C2 and 5C3 catalogues has been made at Jodrell Bank with the Mk IA-Defford interferometer operating at 408 MHz giving a minimum lobe spacing of 1''.2. The technique of phase referencing has been used to carry out long integrations on these sources and a noise level of 5 to 10 mJy was achieved. The observational technique and the factors governing its usefulness are described, and results of the observations of 202 weak sources are presented. The number of weak double sources observed is very much greater than is expected in non-evolutionary relativistic cosmologies, but is consistent with a density evolution of the form rho = rho0(1 + z)5. (author)