I recently bought a digital camcorder and in the box were some ferrite cores, one for the AC adapter and another for the AV cables. The instructions said something about FCC regulations, pertaining to these ferrite cores. I guess my question is, what exactly do they do when they are put on the wire and why are they regulated by the FCC?
They help stop interference from coming in from the adaptor and the cable.
For a bit of info on how these things work and why you need them, try this link, HowStuffWorks dot com, naturally.
Digital electronic products can be both subjected to and be the source of RF noise which can either interfere with the operation of the device or it can transmit RF noise backward into the mains supply line and cause interferance to anyone else connected to those same supply lines, which could end up being say your next door neighbor.
The FCC regulations, which I am not personally familiar with, are likely to be very similar to EU standards and these set limits upon the amount of electrical noise a device may make.Obtaining authority approval is a long and expensive affair.
Electrical noise is a complex thing to regulate because a device will usually produce noise at specific frequencies and virtually none at all at other frequencies but when you calculate the total power this is worked out across a whole range of frequencies or band.
This might mean horrendous peaks of interferance but when it is averaged out across the whole band it might well be very small so maximum limits have to be set for this too.
There are differing standards depending upon where the equipment is to be used and in some environments such as say hospitals in certain sensitive areas patients are not allowed to bring in any personal electrical equipment.
casdavecovers most of it. Most computers and computer devices operate at Radio Frequencies. Sometimes unwanted signals can travel on the outside of a cable. These signals, sometimes called ‘common mode’ can be blocked with the proper use of ferrite beads or cores. Not all ferrite materials are the same. The mix of material that the bead or core is made of is tailored to be most efficient at the desired frequency.
I’m a ham radio operator and we mostly use a ‘43 mix’ which is most effective on the HF bands where most Radio Frequency Interfearence (RFI) occurs from ham radios. Computer devices operating at higher frequencies may require a different mix.
Winding the cable through the core several times is as effective as multiple cores. Cheaper too!
An inductor inserted in series with a conductor will create (along with the source impedance) a low pass filter, i.e. it will attenuate high frequency components of the signal. So by inserting an inductor in series with one (or both) of the AC adapter’s conductors, any high frequency noise induced by the camcorder onto the AC adapter’s cable will be attenuated. This is good, because you don’t want to be radiating high frequency garbage into the environment. And what could cause this? Most likely switching components in the power supply, which cause transients/current spikes in the AC adapter’s cable. But I’m not sure why you would want to insert an inductor in series with your AV cables… sure, there is high frequency information on them, but it’s part of your video signal.
Oh, the ferrite cores… when you wrap a conductor around a ferrite core (or vice versa), you’re making an inductor. Granted it will have a fairly low value, and therefore only attenuate very high frequencies, but it’s better than nothing.