Bunnell main-line telegraph relay


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.

Maker: J. H. Bunnell & Co.

Location: Currently not on view

See more items in: Work and Industry: Electricity, Communications, Telegraph Relays & Repeaters


Exhibition Location:

Credit Line: from Sarah J. Farmer

Data Source: National Museum of American History

Id Number: EM.181946Catalog Number: 181946Accession Number: 2015.0173

Object Name: relaytelegraph relay

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

Guid: http://n2t.net/ark:/65665/ng49ca746b2-a071-704b-e053-15f76fa0b4fa

Record Id: nmah_706910

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