Prior to the
introduction of the Multiple Tuner by the Marconi Wireless Company,
receivers had only limited tuning ability which left them with no
effective way of discriminating between the signals of multiple
simultaneous transmitters. Marconi was well aware of this limitation
which was brought painfully home to him in 1903 during a demonstration
of his wireless apparatus by Dr. J. Ambrose Fleming1.
According to the story, Fleming was about to demonstrate the system when
the Morse printer began chattering rapidly with the words: "There was a
young man from Italy, who diddled the public so prettily..." The source
of this embarrassment to Fleming and Marconi was a business rival who
had set up his own transmitter as an attempt to discredit Marconi.
While the incident was
certainly embarrassing, it did provide Marconi with an excruciatingly
clear message: For wireless to be of commercial value, the ability to
distinguish between multiple transmitters was a must.
Marconi Multiple Tuner
here to see a photo of this piece before
Marconi assigned the
problem to one of his top engineers, C.S. Franklin. Franklin's
solution, for which Marconi obtained a patent in 1907, is a remarkable
work of engineering and innovation.
The set is a major
milestone in radio development and introduced several new technologies,
Multiple Tuner consists of a set of three LC circuits each made up of a
variable condenser and a variocoupler (see the diagram below). By
selecting the appropriate combination of taps on the aerial tuning
inductance, variable condensers and the variocouplers, the operator
could tune over a range of 80 to 2600 meters.