Home audio & video forum: Ferrite cores - to use, or not to use?

Thanks for the response, and particularly the two links provided.

The second link ( to: "Understanding How Ferrites Can Prevent and Eliminate RF Interference to Audio Systems" by Jim Brown (K9YC), Audio Systems Group, Inc.) was terrific. It answers all of my questions, even some I had not yet come up with.

The first link, to a wiki definition was one I had already found but still left me with questions. Thanks a bunch.

Some explanatory background ("principles of electrical engineering 101") and a conclusion with not one (use it, check for heat, and but two bits of applicable advice... love it. Thanks.

But, I still have a minor concern / query. The supplied power cord has two ferrite collars assigned to it (why Samsung did not provide a power cord with these integrated ferrite beads, I have no idea). But they do provide rather precise instructions regarding placement clip around cable near plug "with 3/4 inches (20mm) maximum distance between the ferrite core and the end of the cord" inserted into TV and wall outlet.

But... there is a third ferrite collar. Instructions are to "clip it around cable as shown." The illustration shows what looks like a thin wire with a massive "plug" rather than the coaxial cable and connector of comparatively similar thickness. I have only the one end to work with (at the television) as the other end disappears through a hole in the wall. So, I will clamp it on a couple of inches away from the connector.

Having owned component audio systems since the 1960s, I am surprised to recall only having to install a ferrite core like these once before, and that was within the past couple of years. any idea why their use might be increasing?

Thanks in advance for your help / reassurance. Jim

Source/proof of this?

No, no "proof." All I can offer is my admittedly questionable recollections of buying, installing and using other new electronics. I don't recall any device that came with "Do-It-Yourself" add-on ferrite cores before this Samsung plasma television. In fact, I mentioned (when starting this thread that I recalled installing one earlier, but I since realized that was something else entirely. It looked the same, but was a weight that clamped onto the kitchen sink's sprayer hose, to help the hose retract properly after each use.

So, I checked our two other televisions (both ready for disposal/recycling): neither has ferrite beads on the power cord. Neither was equipped with ferrite for our cable input line, or it would still be there. Looking further, none of our audio components have ferrite lumps (RFI protection) on their power supplies o signal-carrying lines either, despite the congested jumble of speaker wires and wires transferring signal back and forth between my receiver, CD player, DVD recorder/player, television or my (long unused) Teac tape deck.

The only visible use of ferrite RFI protection I found in our home are integrated (inseparable) ferrite beads on the power supply cords that came with our three Dell laptop computers.

We only add them when we can't pass the FCC or other tests. Or when we think it's causing interference.

I can see why folk could get confused about these and wonder why some gear has it and others do not.
Bob

Bob,
Thanks for weighing in.
Three TODA-ISU (part number HT2629S) "ferrite cores" (also known as ferrite beads, chokes or collars) are supplied by Samsung with their highly-rated (see CNET and Consumer Reports) plasma television (PN43E450). Samsung's ferrite devices are split cylinders, designed to clamp onto the power cord at each end, and onto the "antenna cord (not supplied)" where they are supposed to reduce radio frequency interference that would otherwise be picked up by the cables and carried into the television. However, the internal diameter (15 mm) of the ferrite devices is three times the external diameter of the designated cables (5 mm and 6 mm). The ferrite cores attach so loosely, they will not stay where installed (which, according to Samsung's specifications, must be no more than 3/4 inches from the ends of the power cord). If the physical size is far too large will it be too much impedance? Or will leaving a gap between core and cable reduce the amount of impedance (too little)? Also, as my "antenna cable" has been upgraded to a Belkin High Speed HDMI cable (a shielded cable carrying a digital signal), it is not clear that placing a ferrite core serves any purpose on that line.

If you aren't seeing any issues, don't bother with over-analyzing the whole ferrite core nonsense.

Keep in mind that your 'high speed' HDMI cable is another ruse that you bought into .

B... b... b... but "over-anal-yzing is my specialty!!!

If by "another ruse" you are referring to Belkin's use of the "high speed" adjective, I bought the cable for length and price. It was $19.88 plus tax, and the cheapest HDMI cable I saw on the rack. I didn't even notice "high speed" until sorting through the empty
packaging, looking a model number (AV10049-12) which, interesting,
Belkin's own website doesn't recognize. Getting the 43" Samsung for $377.99, and only then hearing the store would pay the $26.46 sales tax... I was so pleased, all I wanted was to go home and, if I could get the thing to fit into our cabinet, watch our new television.

If you are referring to buying the cable at any store, instead of online, you're right... They got me. It never occurred to me (until I was signing for the t.v.) that I would need a cable type I did not already own (I have spools of wire and coaxial). I did not even have to look at my wife to know I would not be dragging her to Radio Shack or KMart to see if I could save another $5 or $10, or waiting for one to come by mail.

Let them off if there is no issues with images or such. Don't over analyze because what we are testing for in the lab is only seen by the equipment (FCC testing.)
Bob

The ferrite core is, as named, the actual magnetic CORE of an inductor, be it a transformer or a single coil, the "shorted turn" only occurs IF a turn of a separate conductor is placed around the ferrite core and the ends shorted together.
The intended purpose of the cores on the power and aerial leads, is to reduce or eliminate the RF interference which may find its way into the device, in this case, the TV, and also to reduce the radiation of switch-mode noise and other interference from within the device and thus protect other devices from the TV "noise".
(Try using a portable AM radio nearby to sample this noise!!)

donhe7