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In Reply to: RE: Re: RFI filters posted by unclestu on January 26, 2011 at 14:20:00
I'm semi familiar with their product line and basically everything you told me I already knew. Anyway, they do work even if minimally. The store where I purchased them had an incredible stock of AC line filters. Due to the economy though, the store closed, went out of business. Bummer.The only real way to avoid all RFI and EMI would be rather impractical. We live in a very "noisy" world. I'd really miss my air conditioner, refrigerator (cold beer), cell phone and clean laundry (washing machine). Basically I'd have to live inside a large RF anechoic chamber and wear an aluminum foil hat!
I'd have no problem placing little squares of carbon fiber on all my ICs, but I'm not quite convinced that it would be the correct thing to do.
Edits: 01/26/11Follow Ups:
Since the purpose of the carbon is to absorb RFI, a piece of regular carbon fiber,a cut square would basically be tuned to only two frequencies ( taking a page from the stealth technology). That's fine when you know the frequency of the offending signal, but a piece of square carbon fiber may not be the pest application.
Back in '91 I used to shield every semiconductor in my CD player with copper foil and ground the shielding: very tedious and painstaking but it yielded very good results ( inspired by the early Wadia DACs with separate compartments for analog,, digital, power supply stages). Doug Blackburn wrote about this particular tweak ( I had sent him a modified unit for examination) in an early issue of Positive Feedback, although by my request, he did not mention my name.
Digital sources of RFI must certainly include the DAC chips, the servo chips, and, indeed, the laser head mechanism itself. Again it is my contention that we must attack the problems at the source rather than using band aids at the tail end. Certainly a close examination of many CD players and other digital sources reveals that a filter circuit is very often employed at the outputs to cut the RF. This can range from a simple cap, as in the Esoteric series, or a simply first order crossover ( cap and resister) or something more complex ( a series of cap/ resistors forming a pi network ( CJ cd player). Shielding chips often means that compensating circuits may have to be removed in order to preserve tonality.
Recently with the advent of ERS paper, I get even better results than the copper foil shielding. I still use it and often use it to construct crude Faraday cages. Leakage is undoubtedly a bit high but it is certainly very effective, and by simply extending the thin paper over the chassis overlap you get decent coverage.
Also check Max's summary of ferrite use. You can cut a tremendous amount of EMI/RFI feedback on the power grid by simply using ferrites over the power lines of offending appliances. I employ ferrites on everything plugged into the wall with the exception of my audio gear with very good results.
Stu
Stu
I'm all for ferrites. I can't help but notice that every time I buy a new peripheral to use with my computer the supplied connecting cable has a molded in ferrite!
I've been GOOGLEing up EMI and RFI absorption/suppression/rejection/shielding etc. Not really a whole lot out there with regards to using carbon fiber. Metal (various alloys) are still the preferred.
That's very true especially in monitors and printers, which all process video or images.
Carbon fiber is actually used in the ERS paper to serve as a ground plane. Check out the specs at the Stillpoints website. They actually publish the RF attenuation at various frequencies. It is quite impressive.
As a spin off of the stealth technology, I see it being employed more often in consumer products with the Japanese manufacturers jumping on the band wagon. Many are specifically engineered for a set RF frequency. The nickel plated carbon fiber shards which contact the carbon fiber ground plane can be cut to specific lengths to "tune" in specific offending frequencies.
IIRC, that is how the military uses the technology since the radar frequencies of hostile nations are fairly well known. The ERS is a more broadband approach, which makes it well suited for home use where you can get all sorts of offending frequencies.
What is interesting is that in my using copper foil to shield the semiconductors, I suspect the metal actually can reflect some RFI, instead of simply absorbing it. I have experimented with those conductive foam you see used by some shippers in packing static sensitive devices. I gave up on them because the foam does deteriorate ( at least where I live), and I was afraid the conductive foam drifting on a PCB with those micro traces may possibly lead to trouble.
Also I find that placing two ferrites on each power line end is significantly more effective than one. Close to the components helps cut the RF from entering the component, closer to the input plug helps clear your power grid. I was buying ferrites by the hundreds, for a while.
Stu
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