  We make a new estimate of the extragalactic radio background down to kHz
frequencies based on the observed luminosity functions and radio spectra of
normal galaxies and radio galaxies. We have constructed models for the spectra
of these two classes of objects down to low frequencies based on observations
of our Galaxy, other normal galaxies and radio galaxies. We check that the
models and evolution of the luminosity functions give source counts consistent
with data and calculate the radio background expected from kHz to GHz
frequencies.
  The motivation for this calculation is that the propagation of ultra-high
energy gamma-rays in the universe is limited by photon-photon pair production
on the radio background. Electromagnetic cascades involving photon-photon pair
production and subsequent synchrotron radiation in the intergalactic magnetic
field may develop. Such gamma-rays may be produced in acceleration sites of
ultra-high energy cosmic rays, as a result of interactions with the microwave
background, or emitted as a result of decay or annihilation of topological
defects. We find that photon-photon pair production on the radio background
remains the dominant attenuation process for gamma-rays from $3 \times 10^{10}$
GeV up to GUT scale energies.
