  In the framework of the cosmological model LambdaCDM the features of
properties of giant radio sources with steep low-frequency spectra of linear
(S) and break (C+) types are examined. Our estimates of characteristic age of
galaxies and quasars with steep spectrum from the UTR-2 catalogue have values
10E7-10E8 years. We consider that steep radio spectra may be formed at the
transient injection by synchrotron losses of relativistic electrons. To further
examination of evolution features of giant sources with steep spectra we
consider ratio of emission of radio lobes and accretion disk (and disk crown)
versus velocity of jet propagation and characteristic age of these objects.
Analysis of obtained relations testifies to periodical activity of giant
low-frequency steep spectrum radio sources.
