An Ṻbertrager is a transformer that has an equal number of turns on its primary and secondary windings. It was used on field telephone lines. It has two jack sockets: one is labeled “P” and the other is labeled “S.” “P” provides the connection to the primary winding and “S” provides the connection to the secondary winding. For the Ṻbertrager to work properly, the resistances across the primary and secondary windings must each be 42 Ohms.
Although Ṻbertrageren could be used to construct Simplex and Phantom Circuits to optimize field telephone lines, they were also used for other purposes.
A Ṻbertrager was used to transition from a single field telephone line to a double line. In a previous article I discussed how single lines and grounding stakes were used near the front lines. For a single line (La + grounding stake) to double line (La + Lb/E) transition, the single line and grounding stake are connected to the Ṻbertrager primary winding via the AP1 and EP2 terminals. The double line is connected to the secondary winding via the AS1 and ES2 terminals.
A Ṻbertrager was also used to isolate military field telephone lines of the Wehrnacht from the civilian telephone lines of the Deutsche Reichspost (DRP). To do so, the double line of the DRP would be connected to the Ṻbertrager primary via the AP1 and EP2 terminals, and the double line of the Wehrmacht would be connected to the secondary via the AS1 and ES2 terminals.
Transition between single and double lines could be done at the switchboard using an Ṻbertrager. Suppose one field telephone line is connected to the switchboard with a single wire (La) and a grounding stake. The other field telephones lines are connected to the switchboard with double wires (La + Lb/E). So a party on one of the double wire lines can speak to the party on the single wire line, the operator must connect the “P” and “S” jack sockets of the Ṻbertrager between double wire line and the single wire line on the switchboard.
Needless to say, using the Ṻbertrager at the switchboard works, but it can be rather problematic for the operator. The operator cannot use his field telephone to talk directly with the single wire line since his phone is connected to the switchboard by two wires. It is just better to use a Ṻbertrager at the Abspannbock or out in the field to transition from a single line to a double line before running the double line to the switchboard.
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WW2 German Field Telephone Equipment 