
Chapter
5
Passive signal processing
and signal transmission
Leaving aside the physical transportation of
written messages (this includes everything from
the runner with a message in a forked stick,
through carrier pigeons, to the Post Office), there
are three main ways of transmitting information
between widely separated locations. These are
communication over wire lines, that is telegraphy
and telephony; wireless communication, that is
radiotelephony, radiotelegraphy, sound and
vision broadcasting; and optical communciation.
Of these, by far the oldest is optical communi-
cation. It includes the semaphore telegraph, helio-
graph and smoke signal ...