Passive elements (transformers and filters) of 1+1 telephone carrier equipment.
The system operates on field lines with active equipment in a separate case.
Used by the UK Military during WW2, designated YB02229 Apparatus Carrier Telephone (1+1)E Terminal Inert.
Used by the IDF during the War of Independence (1948).
Technology: FDM (Frequency Division Multiplexing) and vacuum tubes.
