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Thread: RF absorption

  1. #1

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    Default RF absorption

    Anybody done a mod for this in any of their pieces? Ran across a guy who did and he said it had positive results. Still trying to get more info out of him and what exactly he did, but it sounds like he applied some material inside the chassis. If this a cheap and effective mod, I'm going to look into it more, but the problem is its not a documented mod so google isn't turning up any relevant information. The best I could find was some esoteric cdp using it in their design for improved performance.
    Usher CP-6311, Shuguang S200MK, Shuguang S845MK, Pioneer BDP-51fd, Essence Audio HDACC, Douglas IC's, Douglas Alpha bi-wire SC's, Pangea/Douglas PC's, Epson 8100

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    Can you be more specific on the material used ? Talking to a guy my age, absorption means different things.

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    I'm trying to get that info. It's not shielding, it's actual absorption, reducing the amount of rf instead of simply reflecting. I've tried to find the material but haven't seen anything that stands out for this use.
    Usher CP-6311, Shuguang S200MK, Shuguang S845MK, Pioneer BDP-51fd, Essence Audio HDACC, Douglas IC's, Douglas Alpha bi-wire SC's, Pangea/Douglas PC's, Epson 8100

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    ummm - shunting to RF ground would do that, yes?
    all the best,
    mrh

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    No clue. His theory is that rf is being built up by the digital processing going on. He also mentioned using it in his amp. I'm very unfamiliar with this stuff, but it has intrigued me greatly.
    Usher CP-6311, Shuguang S200MK, Shuguang S845MK, Pioneer BDP-51fd, Essence Audio HDACC, Douglas IC's, Douglas Alpha bi-wire SC's, Pangea/Douglas PC's, Epson 8100

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    http://www.devicetech.com/products-e...ber-materials#

    In specifications I would look at Type A

    Applications
    • Personal computers
    • Mobile phones
    • LCD cables
    • Military equipment
    • Consumer electronics
    • Appliances
    • Laboratory instrumentation
    Telecommunications
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    If something like this ever works, it will be very situation specific. First the unit needs to have an RFI problem, then you need to chose the correct absorption product (maybe there are different products for different RF frequencies, like ferrite chokes), finally physical dimensions and placement will be important.

    Note that Henry W. Ott and Jim Brown who often write about EMI/RFI never suggest this solution.

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    the RF hash around CDPs and DVDPs is extreme - even in standby, a cheap little Maggotbox (Magnavox) I have hooked up at the moment obliterates AM and maims FM reception on an adjacent tuner even when the player's in "Standby" - I have to unplug it to use the tuner :-P
    all the best,
    mrh

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    I keep my electronics in a lead box. Does that count?

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    Here's a link to Mu metal and similar alloys various forms and sizes:
    http://www.lessemf.com/mag-shld.html
    cristo

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    Quote Originally Posted by zingo View Post
    I keep my electronics in a lead box. Does that count?
    That would isolate it, but not absorb it. I know it was in jest, just saying.
    Usher CP-6311, Shuguang S200MK, Shuguang S845MK, Pioneer BDP-51fd, Essence Audio HDACC, Douglas IC's, Douglas Alpha bi-wire SC's, Pangea/Douglas PC's, Epson 8100

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    Quote Originally Posted by cristo View Post
    Here's a link to Mu metal and similar alloys various forms and sizes:
    http://www.lessemf.com/mag-shld.html
    It appears that is shielding material, not absorption material. That won't do any good because its just going to force RF to bounce around in the unit, not eliminate/reduce its presence.


    I'm hoping to hear back from him today with further information.
    Usher CP-6311, Shuguang S200MK, Shuguang S845MK, Pioneer BDP-51fd, Essence Audio HDACC, Douglas IC's, Douglas Alpha bi-wire SC's, Pangea/Douglas PC's, Epson 8100

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    Does it matter if you absorb or reflect the RF, as long as it doesn't reach your equipment?

    Being a HAM, this was my first stop to research this topic: http://www.arrl.org/files/file/Techn...age/Hallas.pdf

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    The principle he was going off is that the RF is created and reflected INSIDE the unit. Shielding it would only prevent it from escaping and would add no benefit since the issue is with it being inside. In fact, by that theory, it could actually be even more "damaging" to the signal. Absorption would help eliminate its presence, thereby (by his theory and experience) providing a better signal due to less interference.

    He feels that this is a possible reason why some people feel certain components sound better in the nude.
    Usher CP-6311, Shuguang S200MK, Shuguang S845MK, Pioneer BDP-51fd, Essence Audio HDACC, Douglas IC's, Douglas Alpha bi-wire SC's, Pangea/Douglas PC's, Epson 8100

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    Quote Originally Posted by zingo View Post
    I keep my electronics in a lead box. Does that count?
    all you need is a Faraday cage :-)
    all the best,
    mrh

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    The reference product in post #6:

    DTi offers the FA Series RF Absorber Materials for the suppression of electromagnetic waves in electronic devices. The FA Series covers a wide frequency range (10MHz ~ 18GHz) to provide excellent suppression of high frequency radiated noise, conduction noise, and electrical surge. The FA Series RF Absorber Material accomplishes this by absorbing electromagnetic waves into heat and suppresses reflected waves.

    Notice that the frequency range is rather high, so it's mostly limited to digital processing circuits.

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    Gotcha on the internal absorption.

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    My company does a significant amount of work with plasma Arc and TIG welding equipment. These devices produce copious amounts of EMI and RFI somewhere in the range of 20K Volts at 1 to 1.5 MHz! This is the equivalent to lightning in the world of semiconductors. We shield everything with woven copper braid or steel enclosures. The most significant way to reduce the effects of RFI & EMI is a thorough grounding protocol and of course a good earth ground. Absolutely no ground loops can exist or something is going to give up its smoke.
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    My Polk fun and my work just crossed paths... My company does RF interference testing for commercial, medical, military equipment. Our business is to measure RF "noise", insure its under the limits (FCC, Mil-Std, FDA) for the equipment, and to suppress the noise if it is not. A google of EMC or electromagnetic compatibility would yield more info. I've worked with Henry Ott and met him many times. My friend the late Dr. Clayton Paul was also a guru in this "black magic science".

    Your friend has the basics of RF Interference down, even to the extent of the point that the device can interfere with itself. The interference comes from the "chip", the crystal oscillator and radiates as an unintentional radio transmitter. Most RF noise in bourne by one device and interferes with another nearby device by means of Radiated Emission (through air) or Conducted Emissions (through AC Mains). But as your friend pointed out, interference can radiate of conduct within the enclosure and have an effect on another part of the same device. Printed circuit board traces or unshielded cables act as "unintentional" receive antenna and couple the noise into the circuit. Grounding, lack of ground loops, shielding, ferrite filters, etc all all components to help suppress noise from a poorly designed circuit (the path from the source of noise).

    Also, there exists a material you speak of, stick-on ferrite absorber material, looks and feels like a flexible refrigerator magnet, it comes in sheets not too unlike dynamat, that can be applied to surfaces to absorb instead of reflect those unwanted radio waves. As one poster here said though, it would be overkill and unnecessary to line the enclosure with this unless there was an absolute issue. These materials are made available to the manufacturer to use to try and reduce noise, not necessarily for consumer market. We have sheets of it in our lab. As well as ferrite beads, and ferrite discs that can be applied right to the top of chips to "contain" noise at the source.

    If you are getting noise in your system, there are soooo many other areas I'd look to first. And if this noise was attributable to poor design, every sample of that model would have it, not just yours.

    But its an amazing science, a fun business to be in and fun to learn about. And your friend is very accurate with his knowledge on it. Sorry to ramble, but my hobbies and my work rarely cross paths!!!

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