paulr

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

I was in Maplins today, and out of curiosity asked if anyone knows what the "bumps" are near the end of cables. One person said they are inline resistors. Another said they are voltage regulators, and a third said she didn't know. Credit to the young lass for being honest, not sure about the other two muppets.

These "bumps" are called ferrite beads or sometimes ferrite chokes. Their goal in life is to reduce EMI (electromagnetic interference). Now you know.

Geek alert over. !!!

joz8968

iTrader: (13)

Yeah, they act as suppressors to eradicate/alleviate the EMI.


More to the point, what are people's favourite AV interconnect to look at?

Mine used to be the humble 2-way audio-only 180deg 5-pin DIN plug and socket (as used on 70's/80's radios/stereos/rad. cass. etc.)...

joey_turbo

iTrader: (26)

I've took some off a USB cable before, as they were annoying. I found them to be magnets.

speedking

I thought it was where the cable had swallowed a large chunk of data and was digesting it. Specifically e-mails that never came out the other end

Flaps

iTrader: (1)

I'd rather stare at your avi than a wire thanks

joz8968

iTrader: (13)

^^^ Ha. Good wuuun.

Leslie

They absorb RF which may have been induced into the cable and could affect the real signal being carried by the cable. They are not guaranteed to be 100% effective.

Les

Coffin Dodger

Wrong

They are there to suppress any interference that may have found it's way onto the cable from whatever you've plugged it into. Otherwise the cable acts like a an aerial to radiate the interference out into the air.

The cable shield / screen should be performing the duty that Les has described.

This has all come about because as of some EU ruling in the 1990's you were no longer allowed to sell electrical equipment unless it was CE marked. Part of the testing you needed to do was to prove EMC compliance (Electro Magnetic Compatibility). The item is tested for radiated emissions, conducted emissions, and interference susceptibility.

It's mostly for the radiated emissions where the ferrite beads on the cables have come about. The equipment under test had to have representative cables attached to all it's inputs and outputs. For something like a computer with a lot of high frequency clocks inside the chassis these signals invariably find a way to couple onto cables connected to the box. Cheap way to suppress them was to add a ferrite bead to the cable close to where it plugs in and this acts as a high cut filter removing all the high frequency emissions from there on.

CD - Electronics Engineer.