Self Connection

Discussions on the equipment used by the Axis forces, apart from the things covered in the other sections. Hosted by Juha Tompuri
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Rotwang M
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Self Connection

Post by Rotwang M » 13 Apr 2022 13:52

The heart of the civilian Deutsche Reichspost and military Wehrmacht telephone systems was the Selbstanschlußanlagen (SA), which translates to the self connection apparatus. In other words, much of the Deutsche Reichspost and Wehrmacht telephone systems worked automatically to connect calls. With regard to the Wehrmacht, this was done via a rotary dial mechanism connected to an automatic telephone exchange by an Amtszusatz or an Amtsanschließer 33.

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Deutsche Reichspost/Wehrmacht Rotary Dial

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Rotary Dial on an Amtszusatz

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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.

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Strowger Switch

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Strowger Switch



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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