Patent ID: 7777152

Claim:
A filter for isolating a two-phase AC power supply from at least 2 kV p-p of power of an HF frequency that is reactively coupled to a resistive heating element, while conducting several kW of 60 Hz AC power from said two-phase AC power supply to the resistive heating element without overheating, said two-phase AC power supply having a pair of terminals and said resistive heating element having a pair of terminals, said filter comprising: a pair of cylindrical non-conductive envelopes each having an interior diameter between about one and two inches; respective pluralities of fused iron powder toroids of magnetic permeability on the order of about 10 stacked coaxially within respective ones of said pair of cylindrical envelopes, the exterior diameter of said toroids being about the same as said interior diameter of each of said envelopes; and a pair of wire conductors of diameter between 3 mm and 3.5 mm helically wound around corresponding ones of said pair of envelopes to form respective inductor windings in the range of about 16 to 24 turns for each said envelope, each of said wire conductors having an input end and an output end, the input end of each one of said wire conductors being coupled to a corresponding one of the pair of terminals of said two-phase AC power supply, and the output end of each one of said wire conductors being coupled to a corresponding one of the pair of terminals of said resistive heating element; and a pair of capacitors connected between the input ends of respective ones of said pair of wire conductors and ground, each of said capacitors having a capacitance that forms a resonance with the inductance of the corresponding one of said inductors at a resonant frequency exceeding said HF frequency, whereby said filter presents an inductive reactance at said HF frequency and has an RF attenuation of over 60 db at said HF frequency.