- In the late 1800's, Alexander Graham
Bell and rival Elisha Gray worked on an invention that would
revolutionize
communications.... The Harmonic Telegraph
- Telegraph wires were scarce and
expensive; number of available pairs limited the number of messages
- Harmonic Telegraph coupled tuning forks
-- via coils not unlike guitar pickups -- to telegraph lines
- Each tuning fork would send a unique
frequency over the wire, causing sympathetic vibrations in its "mate"
at the other end
- First known application of Frequency
Division
Multiplexing (FDM) -- sharing of a communications medium among
different signals via
partitioning by frequency
- The Harmonic Telegraph was eclipsed by
the
telephone, but with the development of vacuum tube amplification and
analog filtering, FDM resurfaced in analog carrier systems -- and in
the world of radio
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