Sheath current filter

A sheath current filter is a component that will either prevent a ground loop on a two-fold earth or ground connection, or the propagation of high frequency, unwanted common mode signals on coaxial cables.

Ferrits stop depending on the type hum in audio systems, continuous in the picture horizontal bars in AV equipment or the propagation of high-frequency noise on cables. Frequently ferrits mistakenly equated with standing wave filters.

Action of various sheath current filter

Depending on the nature of the signal and the present interference situation the following types can be distinguished:

Isolating transformer ( transformer)

Isolating transformers are transformers for low- frequency analog and digital (S / PDIF) audio connections, or more rarely for high frequency antenna cables between antenna and terminal box (Tuner, VCR, TV, etc.). This sheath current filter to suppress by galvanic isolation between input and output low-frequency current on the shield ( the mantle ) and the soul ( inner conductor ) coaxial cables, which can occur at different potentials by multiple grounding. They influence the signal on the basis of their upper and lower cut-off frequency and therefore can also not transmit DC. Furthermore, occur in analog signals to nonlinear distortion.

Capacitive coupler

The spread of ( low ) frequency ripple currents on antenna leads can be prevented by capacitive coupling of the two conductors. Such obtainable as an intermediate connector elements are used as sheath current filter (English: Ground Loop Isolator ) designated mass separator (English groundbreaker ) and have in the signal path and the ground connection coupling capacitors, due to their capacitance value (about 1 nF ) only in the are able to pass frequencies from about 5 MHz - ripple currents can not flow.

Usual capacitive isolation adapter plugs have a limiting frequency of 1 GHz, so that UHF signals they can pass. They can thus be used for FM radio and analog and digital TV channels, including cable TV.

In commercial satellite receivers such mass separator can not be used, since low-frequency control signals and the supply voltage for the LNB must be transmitted simultaneously.

Application

Exchanger bypass flow filters are used in low-frequency signal lines when a ground loop to another can not be prevented. You have an electrical isolation.

Capacitive sheath current filter can be used in antennas and RF cables to prevent ground loops. You have an electrical isolation.