Standing wave filter

from Wikipedia, the free encyclopedia
Ferrite cores as sheath wave filters for interference suppression
Split ferrite core (hinged ferrite) that can be attached to a cable later

Electronic devices that cause high-frequency interference , such as B. computers, can undesirably emit high frequency energy via connected cables. The interference is carried out of the device as a sheath wave , i.e. as common mode interference , and emitted by the cable - the entire cable or its shielding acts as an antenna .

In order to attenuate this interference, the cables are routed through a ferrite core over the entire cross section (possibly several times) . Due to its inductance, this arrangement acts like a choke with one or, if necessary, several windings for common-mode interference . However, the useful signal, which is transmitted as a push-pull signal, does not see any inductance, as the magnetic fields of the currents flowing back and forth on different wires within the cable compensate each other. The mode of operation corresponds to that of current-compensated chokes, which are often also made up of toroidal cores.

Standing wave filters are z. B. used with the following cables:

For retrofitting of suppressor cores around lines, there are split, snap-in ring and ribbon cable ferrites that can be attached to electrical lines. These standing wave filters are also known as clapper ferrites .

Sheath wave filters are mostly made of nickel - zinc ferrite (NiZn ferrite), but they are also available from manganese-zinc ferrites (MnZn ferrites). The former are suitable as filters against interference from 10 MHz to 2 GHz, the latter are more suitable for use against interference in the lower frequency range from 500 kHz to 20 MHz.

A sheath wave filter generally does not work for a cable bundle between two devices, only one of which is earthed. In such a configuration are spreading standing waves as a standing wave from. In the case of standing waves, ferrite core jacket wave filters are only effective in those places where, depending on frequency and wavelength , there is a current bump, but not where there is a current node.

Sheath wave filters are available for different frequency ranges and wire cross-sections.

See also

Web links

Commons : Ferrite Cores  - collection of images, videos and audio files

Individual evidence

  1. ↑ Application note Würth Electronics: Trilogy of inductors . 3. Edition. Swiridoff, ISBN 3-934350-30-5 , pp. 109 .