Electrical signal separating device having isolating and matching circuitry

An isolating and matching device to enable the heating element of a motor vehicle electrically heatable window, not designed specifically to be an antenna or aerial and essentially aperiodic and non-resonant at VHF frequencies, to be used as a receiving aerial, said device being interconnected between terminal leads of said heating element and an aerial feeder circuit of a receiver and having input leads for connection to a motor vehicle D.C. power supply and an aerial terminal for connection to said aerial feeder circuit, comprising in combination:

• isolating circuitry effectively coupled in parallel with said terminal leads and said heating element and connected with said motor vehicle D.C. power supply to permit passage of heating current from said power supply to the said heating element while isolating or blocking passage of RF signals from said heating element to the said power supply, and means including matching circuitry means for effectively matching the impedance of said heating element to an aerial input impedance of the said aerial feeder circuit to thereby effect efficient VHF signal reception, said matching circuitry means including input circuit capacitance means operatively connected in series with an inductance of said isolating circuitry and in parallel with said heating element to bring the said heating element to parallel resonance near the center of the VHF band;
• whereby, via said isolating and matching device, said motor vehicle electrically heatable window forms together with said input circuit capacitance means and said inductance of the said isolating circuit means a parallel resonance in the VHF band and becomes usable as an efficient VHF receiving aerial.