  The 21 cm hydrogen line is considered a favourable frequency by the SETI
programme in their search for signals from potential extra-terrestrial
civilizations. The Pioneer plaque, attached to the Pioneer 10 and Pioneer 11
spacecraft, portrays the hyperfine transition of neutral hydrogen and used the
wavelength as a standard scale of measurement.Although this line would be
universally recognized and is a suitable wavelength to look for radio signals
from extraterrestrials, the presence of ubiquitous radiation from galactic
hydrogen could make searches a little difficult. In this paper we suggest
several alternate standard frequencies which is free of interference from
atomic or molecular sources and is independent of any bias.
