Turns on ferrite for front-panel wiring

[Peter Rossiter]

What is the purpose of the ferrite ring I see in a lot of PCs?

On my PC, the wires going to the front panel are given one turn
around it.

On a technical note, does it make any difference if the loop of
wires through the ferrite ring is tight (all wires close against
the ring) or loose (part of the loop an inch or two away from the
ring)?

 

[Rob Morley]

What is the purpose of the ferrite ring I see in a lot of PCs?

On my PC, the wires going to the front panel are given one turn
around it.

On a technical note, does it make any difference if the loop of
wires through the ferrite ring is tight (all wires close against
the ring) or loose (part of the loop an inch or two away from the
ring)?

EMI supression. I think it's enough that it passes through the ring,
and the loop is just to hold it in place, but I could be wrong.

 

[mike]

mutual inductance, an increase the flux level = a decrease in rf operating
freq.
the more turns, the tighter, the better.
however, for stray RF from a PC a single loose turn is often enough
microhenrys to squash it

mike

 

[ric]

What is the purpose of the ferrite ring I see in a lot of PCs?

On my PC, the wires going to the front panel are given one turn
around it.

Keeping RF noise out of the wires. Not really essential.

On a technical note, does it make any difference if the loop of
wires through the ferrite ring is tight (all wires close against
the ring) or loose (part of the loop an inch or two away from the
ring)?

For this purpose, not really.

 

[Ian Jackson]

mutual inductance, an increase the flux level = a decrease in rf operating
freq.
the more turns, the tighter, the better.
however, for stray RF from a PC a single loose turn is often enough
microhenrys to squash it

mike

The RF choke is probably there simply because some fool of a competitor
fitted one, and customers now expect to see one fitted.

If it has one turn, it's probably that is the absolute minimum necessary
to meet the current EMC radiation specs. Although more turns would
probably be more effective, this would increase the cost.

Ian.
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