polechanger telegraph relay

Description (Brief)
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.
This distinctive-looking relay was known as a “clockface pole-changer” and was designed for use on polar duplex circuits powered by wet-cell batteries. Duplex circuits allowed for simultaneous transmission of two messages on the same line. The circuit design was such that operators could not tell which pole of the battery at a distant station might be on line and mismatched polarities interfered with reception. The clockface pole-changer could switch the polarity of the battery at the receiving station to eliminate the problem.
Location
Currently not on view
Object Name
telegraph pole changer
telegraph relay
date made
ca 1900
Physical Description
glass (overall material)
grass (overall material)
wood (overall material)
plastic (overall material)
steel (overall material)
Measurements
overall: 5 in x 8 1/2 in x 4 3/4 in; 12.7 cm x 21.59 cm x 12.065 cm
ID Number
EM*331665
catalog number
331665
accession number
294351
collector/donor number
13-14
See more items in
Work and Industry: Electricity
Communications
Telegraph Relays & Repeaters
Data Source
National Museum of American History, Kenneth E. Behring Center

Comments

Add a comment about this object