VLF/HF EMI filter

Claim 1

In a relatively low frequency (LF) radio receiver system having an associated loop antenna operating in close proximity to a much higher frequency (HF), high power transmitting antenna, a LF radio receiver and a shielded signal conducting cable, an EMI filter comprising: a single point system ground; one or more first filter means, electrically connected to said system ground, said signal cable and said LF reveiver, for eliminating HF differential mode and common mode undesired EMI signals induced into said LF radio receiver loop antenna by transmissions from said proximate HF antenna by conducting said differential mode and common mode EMI signals on said loop antenna and said signal cable to said system ground, each said one or more first filter means further comprising a number of discrete reactive elements cooperatively connected to form a low pass filter which is balanced with respect to said system ground, for passing radio frequency signals of relatively low frequency while rejecting said HF EMI signals on said loop antenna; and one or more second filter means, electrically connected to said system ground and said signal cable shield, for intercepting and eliminating HF common mode EMI signals capable of being conducted to said low frequency radio receiver by conduction means other than said LF receiving loop antenna by conducting said common mode EMI signals to said system ground, said conduction means further comprising reradiation from RF shields and direct radiation paths.