Shielding for FM tuner?

Hi Broubin,

Yes, a sheet of copper will act as a shield, so will aluminum or even mild steel, but not stainless steel. It will have to be grounded in order to drain any rfi/emi though. Before trying that, be sure that your tuner's power cord and antenna lead are nowhere near the cd player's power cord. I had the same problem with a cdp a couple of years ago and simply repositioning the coaxial cable solved the problem.

Both your CDP (actually the DAC part, not the transport part) and your computer are putting out RFI (radio frequency interference) from their power cords, which act like transmitting antennas (even though the power cord may have a ferrite collar at the component end.)

To prevent this, you need to replace the regular 3 conductor power cords with ones that have a foil shield (and preferably, a braided shield as well.) The shield(s) must be "floated" from the component end. That means the shield(s) are connected (together with the green ground wire) to the ground pin of the AC plug end only, and not to the ground pin at the component end.

The good news -- that oughta do it. The bad news -- shielded cords with floating shields are hard to find at retail stores.

Unfortunately, you can't just run out and buy one at Best Buy or CompUSA because of what it costs big manufacturers to get a UL listing on such items. However, they're easy enough to make yourself by cutting off the IEC end of a commercial shielded cord and then re-terminating it with a new IEC connector but without the shield connected to it.

If you're not so inclined, many of the specialty manufacturers of audio power cords make them with floating shields in a variety of price ranges, and most of them are represented here on Agon.

ferrite core clamp on filters on the AC cords outght to do the trick: Audioquest makes 2 models, I'd guess the larger ones would work better for this situation.

The problem with ferrite core clamp on filters is that they saturate with radio frequency energy very quickly, even the big fat ones, and once they do, they might as well not be there.

I'm tellin' ya, if you really want a quiet FM background, put floating shielded power cords on all your digital equipment (including CD transports) and if you want to use the ferrite filter somewhere, put it on the FM tuner's power cord, right where it enters the chassis.

Not only are there different size ferrite chokes, but there are also different grades of ferrite. On top of that, there is NOWHERE near the amount of RF leakage coming out of ANY audio related device to ever "saturate" any of the common ferrite's sold for this purpose. If there was, we would all have cancer due to RF exposure. Any leakage that is taking place can probably be measured in milliwatts of power, not kilowatts.

Personally, i would look at both the routing and construction of the interconnects, power cabling and antenna feedling being used on both the components and the computer. The use of some relatively inexpensive but well shielded power cords like the Belden aka "Volex" designs may solve your problems and / or take you at least a step in the right direction. These can typically be had for appr $10 apiece if you do some shopping.

Making sure that your antenna feedline is properly terminated ( solid connector on the cabling with a solid connection to the tuner ) would also be inexpensive and a potential step in the right direction.

After that and if cable routing doesn't solve your problems, you might want to try some shielded interconnects. Grounding all of the component chassis outside of the AC cords may / may not help here too.

These are all very basic and inexpensive approaches to solving your problem as you didn't mention anything about what you were willing to spend to correct the problem. Sean
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