Within the zone, which covers roughly a 160-kilometer ( 100-mile ) radius into much of eastern West Virginia and western Virginia, radio, television and cellular-telephone transmitters are required to point away from the valley to avoid causing interference.
22.
Carbon microphones, usually modified telephone transmitters, were widely used in early AM radio broadcasting systems, but their limited frequency response, as well as a fairly high noise level, led to their abandonment in those applications by the late 1920s.
23.
The water transmitter described in Gray's caveat was strikingly similar to the experimental telephone transmitter tested by Bell on March 10, 1876, a fact which raised questions about whether Bell ( who knew of Gray ) was inspired by Gray's design or vice versa.
24.
When Gray applied for a patent for the variable resistance telephone transmitter, the variable resistance ) invention, as in his caveat of 14 February 1876, his failure to take any action amounting to completion until others had demonstrated the utility of the invention deprives him of the right to have it considered ."
25.
In 1924, Robert Mathes of Bell Telephone Laboratories filed a broad patent covering essentially all electromechanical delay lines, but focusing on acoustic delay lines where an air column confined to a pipe served as the mechanical medium, and a telephone receiver at one end and a telephone transmitter at the other end served as the electromechanical transducers.
