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Deutsche Reichspost/Wehrmacht Rotary Dial
Rotary Dial on an Amtszusatz
The Amtszusatz is Set for ZB/SA Operation
The rotary dial was an electrical switch. The dial momentarily actuated electrical switch contacts a certain number of times, depending on how far it was rotated. The number of switch contact actuations corresponded to numbers 1 though 0 and letters A through K. This created a series of electrical pulses for each digit and letter of a phone number.
In the automatic SA exchange, various electro-mechanical devices were activated by the rotary dial’s electrical pulses to automatically self connect the call. The most common device was the Strowger Switch which connects calls by a “step-by-step” process.
Unlike today’s modern direct dial civilian telephone systems, the WW2 German SA system was not as fully automatic as the name implies. It required the switchboard operator to use the rotary dial of the Amtszusatz to connect to a network of automatic exchanges over various branch and trunk telephone lines. The exchanges were connected by at least one telephone line.
Switchboard operators were provided with a map showing the network of telephone lines and exchanges. Before connecting a call, the operator had to use the map to plan which branch lines, trunk lines, and exchanges he or she was going to go through to complete the call connections. If a telephone line was busy or damaged, the operator had to select a different route to complete the connection.
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