cable beads

[Thunderchild]

are those ferite beads on cables actually of any practical use

 

[dknguyen]

Yes they are.

 

[Thunderchild]

how the cable is sheilded why do some usb cables have them and some not

 

[dknguyen]

THey don't shield the cable. They stop the cable from acting as an antenna by shorting out the higher frequencies. It is similar to sticking an inductor in parallel with an antenna. THe ones you see are probably just clamp onto the wire once, but others existing where you wind the wire around a ferrite ring to almost make an inductor-type thing.

 

[Nigel Goodwin]

Yes they are.

A rather sweeping statement?

A more correct one might be "they may be useful, in very rare and exceptional circumstances".

 

[Thunderchild]

A rather sweeping statement?

A more correct one might be "they may be useful, in very rare and exceptional circumstances".

thanks migel better tel the how stuff works website that their nuts

 

[arrie]

Yes, it's to counter frequency.
and you only have to loop the wires through the ferrite once.
Many times also you will find the ferrite only on one side of the cable.
Some PC suppliers even provide a ferrite ring for use with the cables that drives the LED's and stuff on the front panel to stop RF.
I think it's an overkill, but very nice idea.

I used to make up harnesses for a tracking company in recent times, now these guys are really strict about RF, if you want to put a unit in Merc, Merc will take your unit and really pull it apart in tests for RF.
In any case, this also involved pulling the harness through a ferrite ring.
Heavy on the hands if you want to do a couple of thousand of these.
It would take me about 2 minutes to do the whole thing with heat shrink the lot.

 

[Thunderchild]

well I've never seen any loops, the cores (as stated by "how stuff works" themselves) is just threaded with the wire no mentiong of any loops through it, and again the cables are screened so whats the odds ?

 

[JimB]

The purpose of the ferrite "bead" is to stop conducted RF emissions passing along the cable. Similarly it will prevent external RF from being conducted into the device to which it is connected.
Whether they are required all the time in all positions is open to debate, however it is good engineering practice to have them. (Either that or properly screened boxes with filters on every cable entering or leaving the box).

JimB

 

[arrie]

That should be sufficient information, according to my knowledge the cables are looped around the bead once.
Maybe my use of language is misleading. Brief explanation follows:
All cables are pulled through the circle inside formed by the bead, then over the outer edge in a loop-de-loop fashion, and through the inner circle again.
Maybe there are other practices.

Sorry I'm not implying anyone to be stupid, but when I looked at my original statement, not even I was sure how the loopy business are taking place, so if anyone is stupid, it's me.

 

[ericgibbs]

That should be sufficient information, according to my knowledge the cables are looped around the bead once.
Maybe my use of language is misleading. Brief explanation follows:
All cables are pulled through the circle inside formed by the bead, then over the outer edge in a loop-de-loop fashion, and through the inner circle again.
Maybe there are other practices.

Sorry I'm not implying anyone to be stupid, but when I looked at my original statement, not even I was sure how the loopy business are taking place, so if anyone is stupid, it's me.

hi arrie,
I agree.
Often they are looped back thru, it makes a complete turn around the ferrite bead, makes it more inductive therefore more effective.

 

[arrie]

Thanks Eric, now I don't feel that stupid any more.

 

[rita.jones56]

A rather sweeping statement?

A more correct one might be "they may be useful, in very rare and exceptional circumstances".

Yeah I think that's more like it.