Electrical signal separating device for combined windshield antenna and heater grid

Claim 1

An electrical signal separating device for separating a radio signal from the resistance heating element of an electrically heated window, comprising: an electrical circuit having input terminals for connection to a motor vehicle d.c. power supply, power output terminals for connection to the heating elements, and a radio signal output terminal for connection to the aerial circuit of a radio receiver for feeding radio signals picked up by the heating element to the receiver; said circuit further including a blocking circuit for blocking passage of said radio signals to the power supply, wherein the blocking circuit comprises a bifilar coil formed by two wires wound on a common core and defining two concentric coils, the coils being interposed respectively between the said input terminals and power output terminals and being mutually coupled and arranged so as to provide high impedance paths for in-phase fluctuating currents at said power output terminals but low resistance paths for currents flowing through said circuit from the d.c. power supply, said resistance heating element acting as a conductive sheet to radio signals, whereby the bifilar coil effectively blocks the radio frequency signals, while passing the current from the d.c. power supply to the heating element.