Telegraph Sounder

Description
Telegraph relays amplified electrical signals in a telegraph line. Telegraph messages traveled as a series of electrical pulses through a wire from a transmitter to a receiver. Short pulses made a dot, slightly longer pulses a dash. The pulses faded in strength as they traveled through the wire, to the point where the incoming signal was too weak to directly operate a receiving sounder or register. A relay detected a weak signal and used a battery to strengthen the signal so that the receiver would operate.
So-called “pony” relays like this unit made by J. H. Bunnell & Co., serviced private lines and shorter branch circuits. The resistance of a given pony relay varied depending on the length of the circuit. This 50 ohm pony relay would have been used on circuits up to about 45 miles in length.
Location
Currently not on view
maker
J. H. Bunnell & Co.
Physical Description
wood (overall material)
metal (overall material)
brass (overall material)
Measurements
overall: 3 1/2 in x 3 in x 6 in; 8.89 cm x 7.62 cm x 15.24 cm
ID Number
EM.314488
catalog number
314488
accession number
203371
Credit Line
from Weston Electrical Instrument Corp.
See more items in
Work and Industry: Electricity
Communications
Telegraph Relays & Repeaters
Data Source
National Museum of American History, Kenneth E. Behring Center

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