main-line telegraph 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/used by [name] 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 has a 170 ohms rating, somewhat higher than usual.
Location
Currently not on view
Object Name
telegraph relay
Physical Description
brass (overall material)
wood (overall material)
steel (overall material)
plastic (overall material)
Measurements
overall: 3 3/4 in x 9 in x 4 1/4 in; 9.525 cm x 22.86 cm x 10.795 cm
ID Number
EM*331766
catalog number
331766
accession number
294351
collector/donor number
100-014
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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