This diagram illustrates the idea of having a strong "Signpost" beacon
signal at one frequency and the weaker wideband "Main Signal" at another.
It is more likely that the beacon or acquisition signal would be adjacent to the
wideband data signal or even part of it. That is why, the COSETI Observatory is looking
for "the lighthouse in the sky" beacon in the optical spectrum, where it is
expected the wideband signal would be co-located. It is very difficult if not impossible
to transmit a wideband signal over interstellar distances due to interstellar dispersion
and scintillation effects.
