Purpose of Ferrites (NOT Ferrets)

[Mike Smith]

Raymarine recommends using ferrites (NOT ferrets) on cable connections close to their instruments.  What is the purpose of the ferrites?

Mike

[Craig Illman]

I'm sure some more knowledgable EE will chime in, but I think the purpose is to keep the wire from acting like an antenna and transmitting the signal passing through it.

- Craig

[rirvine]

Close – the ferrites on cables are to prevent the high frequency EMI generated inside the box from radiating down the cable and hence either into other pieces of equipment through the cable (especially the power and ground wires) or from the cable out into the air to interfere with other stuff – AM/FM radios and VHF radio.   Usually the biggest EMI offender on a boat in the battery charger - mostly likely from the switching regulator to conver AC to DC. You will find that cables on PC have them for the same reason – to stop conductive EMI leave the box.

Bottomline is - put them on as life will be better with them.

hope this helps!

[Sailing Steve]

RIrvine is absolutely correct.  They are basically a carbon type material that you coil your wire(s) around, or place the ferrite core around the wire.  They are the lump you find on the monitor cable of your computer for example.  You can find generic cores of various shapes and sizes at most electronic supply houses, possibly Radio Shack - fairly inexpensive.  They are great for removing electrical noise from many things such as telephone lines etc.  EMI = Electro-Magnetic Interference.