Empire State Filter Co.’s line of hum eliminators, also referred to as a humbucker or a ground loop eliminator, is designed to remove interference created by long cable runs, 60 cycle power demands, grounding noise, and magnetic coupling. Normal voltage differences between system grounding points cause small AC power currents to flow through video cables. At power frequencies, a voltage drop of only 7mV peak can cause a visible hum bar.
How a hum eliminator works: 60 cycle hum - ground loop current - only flows on the shield of a coaxial video cable. This current will produce a magnetic field in the iron core of the hum eliminator and create an inductor, or choke. The high impedance of this choke - in the ground path - effectively eliminates the 60 cycle hum from passing through the unit. The video signal, on the center conductor, is shielded from this impedance - by the cable's shield - and passes through the unit unaffected.
The major advantage using a hum eliminator over an isolation transformer is high bandwidth. The low-frequency response extends to DC avoiding an effect, seen on waveform analyzers, called field-rate tilt and the high-frequency response of 100 MHz or more make these units suitable for high-definition and projection systems. These units are passive devices which remove induced hum while being transparent to the video signal.
Single channel units are designed for composite signals, multi-channel units can be used either for multiple composite signals, component, YCbCr, or RGB plus sync signals. Other models are also available with internal audio ground loop isolators to remove both audio and video interference.