American telegraphy and encyclopedia of the telegraph; systems, apparatus, operation (1909)
Maver, William, jr. [from old catalog] · New York, Maver publishing company · leaf 313
SON-SMITH DUPLEX. This duplex is arranged to operate with battery at one end only. It may beclassed as a combination of the Stearns duplex and the polar duplex. Such aduplex is occasionally of utility when it is not feasible to place a battery at bothterminal stations. The principle of the duplex…
Telegraph
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