sundance-communications.com/forum Forums General General Telephone & Systems Information Ferrite beads?

It increases the inductance of the cable or wire which will suppress any RF from traveling through it but allowing DC and sub RF AC.

The main reason they abound is to keep leakage below FCC required levels. We are seeing more of them lately on all kinds of connecting cables and cords because devices are running faster and faster and the RF frequencies generated by the clock and busses are a problem if they get out of the housings. Computer and other equipment housings can easily be made RF tight but the connectors and cables are like holes in a screen door.

-Hal

Does the ferrite bead have to "engineered" for a specific cable or application? Or will just any old ferrite do?

Richard

Thanks to all, but it still doesn't compute with me. How can a simple piece of ceramic that's not even physically in contact with the cable core do all of this work? I could understand if we were talking about grounded and bonded shielding.

From the HOWSTUFFWORKS link in Merrits post.
"A ferrite bead is simply a hollow bead or cylinder made of ferrite, which is a semi-magnetic substance made from iron oxide (rust) alloyed with other metals. It slips over the cable when the cable is made, or it can be snapped around the cable in two pieces after the cable is made. The bead is encased in plastic -- if you cut the plastic, all that you would find inside is a black metal cylinder."

Think how the copper wire wound around the iron nail makes a magnet.

Excess freq/EMI "charges" the ferrite --- a limiter per se.

The molecular composition inside the ceramic is the component. The ceramic is just a means of containing it.

Boy, did I have to dumb that down for me. :read:

How wrong am I? I only read the first 3 articls.

For what it's worth, this is the explanation I got in Navy electronics school...

Any conductor that has current passing thru it, generates a magnetic field around it, called the Corona Effect..most notably used in photocopiers. RF signals can use this magnetic field as signal path, meaning it can ride along the conductor doing lots of insidious things. A torroid or ferrite bead messes up this nice clean field, confusing the sneaky RF signal so it can't get to it's ultimate destination.

As a disclaimer, at the end of this explanation, the instructor asked us to push the "I Believe Button"...

Explanation of how it works.

https://www.murata.com/emc/knowhow/pdfs/te04ea-1/23to25e.pdf

I have ferrited out some good links for us dummies:

https://computer.howstuffworks.com/question352.htm

https://computer.howstuffworks.com/framed.htm?parent=question352.htm&url=https://www.antennex.com/shack/Dec99/beads.htm

Now is this the same thing as a ferrite bar? I have on on an old Panasonic amp, says not to get it near any wiring on the system. The ferrite bar is wired into the unit, and sticks out sideways from the unit.

ferrite is used in many different applications and comes and different forms They work in the same way that a coil or capacitor work with ac/dc the material that makes a ferrite bead/bar is composed of non conductive compound impregnated with a conductive compound depending on the different size, type, ratio and shape they will effect different frequencies in different ways. think of them as a passive reactive network (choke/coil circuit)