Bunnell main-line telegraph relay

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.
“Main line” relays like this unit made by J. H. Bunnell & Company were one of the most common types of relay and were typically made with a resistance of 150 ohms. As the name suggests, main line relays served on major intercity circuits several hundred miles long. This relay was used in experiments by the noted electrical inventor Moses Farmer.
Location
Currently not on view
maker
J. H. Bunnell & Co.
Physical Description
wood (overall material)
brass (overall material)
steel (overall material)
plastic (overall material)
Measurements
overall: 3 1/2 in x 8 1/4 in x 4 1/2 in; 8.89 cm x 20.955 cm x 11.43 cm
ID Number
EM.181946
catalog number
181946
accession number
2015.0173
Credit Line
from Sarah J. Farmer
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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