The "Athearn" type Morse repeater was patented November 14, 1904. The inventor was William E. Athearn of the American Telephone and Telegraph Company. This type of repeater was manufactured by Western Electric and was used extensively by American Telephone and Telegraph.
A "repeater" is an instrument or collection of instruments that is designed to increase the distance over which telegraph communications can be transmitted and received. For an excellent explanation of the necessity of repeaters, read George P. Prescott's introduction to the subject of repeaters.
The technical operation of the Athearn repeater is fascinating. The first place to start is the original patent. The patent is reproduced in its entirety here.
The best practical explanation of the Athearn Repeater is found in "List of Specifications Included in Handbook of Central Office Telegraph Practice". This is a pocket sized reference book intended for use by AT&T engineers and technicians. This book describes the theory of operation and includes information on the installation of the Athearn repeater and associated equipment. An excerpt from this book includes diagrams and photographs of the Athearn Repeater.
Surviving examples of the Athearn repeater are rare, and rarer still are photographs of the instrument in use. The following are images of a surviving 3-A model. Click on the image for a closer, more detailed image.
The following images show the AT&T telegraph office in Philadelphia Pennsylvania as it existed in 1920. This installation was located in the Bourse Building, which is located about 200 yards from Independence Hall in downtown Philadelphia. This impressive photograph shows literally tons of operating telegraph equipment. Click on these images for a closer view- note the Athearn repeaters located on the top shelf of the first row of equipment.
Zooming in on the first row of equipment, some interesting details are seen. Note the "listening stick" lying in the left instrument bay. This was sort of a "stethoscope" for telegraph relays, which was used in a noisy office to inspect a relay for proper operation. An Athearn repeater can be seen in the upper left corner. The 2 keys immediately below the repeater are used to work the east and west circuits individually for testing purposes. Read a detailed description of this fascinating and rare image.
Each equipment bay contained a bridge-polar duplex set. The pole-changing relay, repeating sounder, and line balancing networks can be seen in this image. AT&T used "composited" telephone circuits to obtain working telegraph circuits. This method was used to simultaneously transmit telephone and telegraph signals on the same wire lines. This resulted in a substantial cost savings, as the wire lines are the single most expensive component of a long-distance communication system.
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