Communication for the Furiour
page for German WW II equipment
Lichtsprechgerät, pictures taken
at Helge Fykse (LA6NCA)
Read LA6NCA's notes
We are not quite sure about what intentions have been made as to connect this equipment to the telephone line, but suppose
this could be a solution to connect it in series with the field-telephone
The basic circuit for balancing 4-wire to 2-wire circuit line with minimum sidetone is derived on the wheatstone bridge.
Balance is achieved when the transmitter doesn't cause audio into the receive side. Normally such simple circuit will have a
practical balance of 20-28dB, but the normal telephone subscriber line has an impedance of 620W in series with 1µF and 47nF in
paralell, or say 700 ohm nominal impedance for those who don't understand imaginary expressions in electronics (@800Hz).
Lumped equivalent to standard subscriber lines in Europe
(or my experience for setting up 2W/4W telephone equipment for minimum return from the subscriber line)