Bunnell main-line telegraph relay
date: label: date made
content: ca 1890
name: label: maker
content: J. H. Bunnell & Co.
notes: label: Description
content: 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.
label: Description
content: “Main line” relays like this unit made by J. H. Bunnell & Co. 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 particular unit is rated for 200 ohms, a somewhat higher than normal resistance. A notation in the record refers to this relay as "R.R. Pattern". Presumably that means the piece was made or used specifically for railroad telegraph lines but the exact meaning is unclear.
label: Location
content: Currently not on view
setName: label: See more items in
content: Work and Industry: Electricity
label: See more items in
content: Communications
label: See more items in
content: Telegraph Relays & Repeaters
dataSource: label: Data Source
content: National Museum of American History
identifier: label: ID Number
content: EM.320011
label: catalog number
content: 320011
label: accession number
content: 243907
objectType: label: Object Name
content: relay
label: Object Name
content: telegraph relay
physicalDescription: label: Physical Description
content: wood (overall material)
label: Physical Description
content: steel (overall material)
label: Physical Description
content: iron (overall material)
label: Physical Description
content: brass (overall material)
label: Physical Description
content: plastic (overall material)
label: Measurements
content: overall: 3 1/4 in x 8 in x 4 3/4 in; 8.255 cm x 20.32 cm x 12.065 cm