Ferrite Beads

[bluestrobe]

I just bought a bulk pack of Ferrite Beads at a local rummage sale for a cheap price (ferrite blocks encased in plastic that clamp over cables to reduce interference for those who don't know).

Are these just a waste on networking cabling (I have a couple of 50ft patch cable runs in the house) or are they worth using? If not, what are a good use for these?

 

[ScottMac]

Depending what kind of ferrite you got in them beads (there are ~six or so different types), it can easily kill the network signaling. Ferrites should not be used on UTP carrying Ethernet.

What kind of noise are you trying to suppress?

Between the cabling technology and the transceiver technology, 10/100/1000 Ethernet does a pretty good job of ignoring / negating common mode noise.

If the runs you are having problems with are hand-made, start there; replace them with commercially produced cables.

Good Luck
Scott

 

[cmetz]

I have seen SOHO network devices that include ferrite chokes for cat5 cables. Given how ruthless cost optimized SOHO devices are, I wouldn't think they'd include them unless there was a reason. I wonder if that's a hack for not getting the NEXT/FEXT properties of the jack and PCB traces right?

RF/EMF is a bit voodoo. (but what do I know, I'm just a EE) I would not go doing anything like putting chokes on a line unless there was an actual problem for which chokes were the right solution. They strike me as being likely to cause as many problems as they solve.

Note that for different kinds of signals (e.g. VGA cables) EMF chokes do help, but 10/100/1000 - BaseT are a very different signalling than that.

 

[bluestrobe]

No current problems. Just figured I would put my cheap found bag to work. I'll find something else to use them on then.

 

[ScottMac]

DC Power cables are a good place for those, more often as not.

There are a number of different ferrite compounds used for the beads & clamp-on suppressors. Each variant tends to work within different frequency and proximity windows, and have varying levels of suppression.

Basically, try 'em: if they work, cool, if not, try for something else or paint 'em and make lil Transformer robots out of 'em or something.

Good Luck
Scott