Radio transmission on 230- and 400-kv lines

IN SWEDEN the power lines for high voltages of 230 to 400 kv cause serious interference for radio listeners living in the vicinity of the power lines, particularly in the northern part of the country where the radio field strength of the broadcasting transmitters is low. The measures formerly adopted with a view to overcoming this interference, which mainly took the form of cabling the telephone and low-tension lines and moving the aerials further away, were found to be very costly and ineffectual in many instances. A new method has now been investigated, however, which has yielded successful results. It is based on the transmission of the radio program directly over the interfering line. The principle followed consists in the connection of a radio transmitter to the power line through a capacitor located in a suitable position in the line system (see Fig. 1). The transmitter output is so selected that the signal level for the radio program transmitted over the line exceeds the interference level from the power line by such an amount that the interference is no longer perceptible. Reception can take place in the usual manner by turning the receiver to the wavelength of the power-line transmitter, with no special adjusting.