EMI/RFI Filter Basics

How EMI/RFI Filters Work

Genisco EMI/RFI (Electromagnetic Interference/Radio Frequency Interference) Filters are designed to reject selected frequencies (or interference) that are present on a power or signal line. Our EMI/RFI filters consist of only passive elements (inductors, capacitors and in some cases resistors) in selected combinations to block Electromagnetic Interference (EMI) caused by electromagnetic induction (conducted emissions) or electromagnetic radiation (radiated emissions). When this unfavorable interference in located within the transmitted radio frequency range it is considered Radio Frequency Interference (RFI). Genisco EMI/RFI filters are made in metal housings in order to shield our filter output from exposure to any radiated interference.

Common sources of EMI/RFI interference include: electrical power lines, cords or wiring (these work as antennas to pick up or contribute to radiated interference), switching power supplies, AC motors and microprocessors. Genisco EMI/RFI filters will protect your equipment from this interference in order to prevent malfunction of electronic equipment, possible data loss and degradation of electronic equipment. EMI/RFI filters are applied to both the input and output power lines in order to ensure no external interference affects your equipment.

Standard EMI/RFI Filter Types

Low Pass

Low Pass filters allow lower frequency signals to pass through the circuit, but provide high impedance to high frequency signals. This attenuates (lowers the magnitude of) high frequency signals as shown in the example graph below.

Generally AC Power systems run at either 50 Hz, 60 Hz or 400 Hz, so all Genisco Power Filters are Low Pass Filters. Our filters allow the lower frequency power signals to pass through the circuit, and block the unwanted higher frequency noise.

 

High Pass

High Pass filters allow higher frequency signals to pass through the circuit, but provide high impedance to low frequency signals. This attenuates (lowers the magnitude of) low frequency signals as shown in the example graph below.

Band Pass

Band Pass filters allow signals within a certain frequency range to pass through the circuit, but provide high impedance to all other frequency signals. This attenuates (lowers the magnitude of) all other frequency signals than the ones allowed to pass as shown in the example graph below.

Band Stop or Band Reject

Band Stop or band Reject filters allow all signals except for a certain frequency range to pass through the circuit, but provide high impedance to the frequency signals within a certain range. This attenuates (lowers the magnitude of) the signals within this specific frequency range as shown in the example graph below.