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Thread: RFI shielded Computer Case

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  1. #1

    Default RFI shielded Computer Case

    I have a computer in my shack and once and awhile, its affected by RF from my transmitter causing it to "lock up". I been thinking of repackage it into an industrial computer cabinet that may have better shielded than what I currently have. Any suggestions as to where I can find a old shielded PC cabinet made for industrial use?

    Thanks,
    Greg W8NGA

  2. #2
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    Are you sure the case is the problem? Usually this type of problem is from RF picked up on wires going to keyboard, mouse, network, etc. Try unplugging as many things as possible from the computer and see if it still locks up. Then you can try ferrites on the problem devices.

    Tor
    N4OGW

  3. #3
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    Quote Originally Posted by N4OGW View Post
    Are you sure the case is the problem? Usually this type of problem is from RF picked up on wires going to keyboard, mouse, network, etc. Try unplugging as many things as possible from the computer and see if it still locks up. Then you can try ferrites on the problem devices.

    Tor
    N4OGW
    This is true unless you have a case that is plastic.

    I would invest in some snap on chokes and try that fist.
    When it's time, and it may be sooner than you think.

  4. #4
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    Actually, the first thing I would do is try to get the RF out of the shack. Have you tried a line isolator?

    73,
    Bill
    Member: Backyard Engineering Group

  5. #5
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    If it's a Steel or Aluminum case, and 95% of desktops are, you need to bond the case of the computer to the rest of your ground system, the shorter and heavier the better. That should knock a bunch of the RFI down. If it doesn't, start adding ferrites to all the lines coming into and out of the computer, all of them.

    What I did was ground the case to the single point ground buss in the shack, then went and bought several USB extension cables and audio cables. I bought some #31 mix 2.4" toroids and wrapped the entire cable about them so that they are as close to the computer as possible. For those cables that are too big to get a decent number of turns on the toroid I used snap-ons.
    ACH,
    Member ARRL, SKCC #215, NAQCC #3441, FISTS #11993

  6. #6
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    are you by chance using a USB hub? that was the culprit in my shack---a toroid around the usb cord from the hub to the PC eliminated the problem--before, just one bit of RF and i had to re-boot...........
    [B]MY life is not a journey to the grave with the intention of arriving safely in a pretty and well preserved body, but rather i will skid in broadside, thoroughly used up, totally worn out, and loudly proclaiming...
    WOW... What a Ride![/B]
    [SIGPIC]
    [/SIGPIC]

  7. #7
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    There are some nice rack mount cases available, That typically have good shielding, and are used for Repeater control computers.

    http://www.newegg.com/Product/Produc...82E16811182566

    Even the plastic computer cases have thin metal shielding.

    It would be best to eliminate the RF in your shack, than trying to shield the computer better.

    Sometimes a old Filing cabinet makes for good RF shielding, as long as you vent it for cooling.

    But as mentioned it is most likely something connected to your computer, and RF in the shack.
    "Theory only works perfect in a vacuum." KA9JLM Don

  8. #8

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    Quote Originally Posted by KA9JLM View Post
    There are some nice rack mount cases available, That typically have good shielding, and are used for Repeater control computers.

    http://www.newegg.com/Product/Produc...82E16811182566

    Even the plastic computer cases have thin metal shielding.

    It would be best to eliminate the RF in your shack, than trying to shield the computer better.

    Sometimes a old Filing cabinet makes for good RF shielding, as long as you vent it for cooling.

    But as mentioned it is most likely something connected to your computer, and RF in the shack.
    Don't make such a wide generalization. there are plenty of (read: cheap) "plastic" cases on the market that offer little if any shielding, and to make matters worse (at least from an RFI standpoint,) some older less well shielded cases get reused for newer computers. Shielding or filtering the cables coming OUT of (or into) the box can eliminate much of the interference.

  9. #9
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    Quote Originally Posted by WA9SVD View Post
    Don't make such a wide generalization. there are plenty of (read: cheap) "plastic" cases on the market that offer little if any shielding, and to make matters worse (at least from an RFI standpoint,) some older less well shielded cases get reused for newer computers. Shielding or filtering the cables coming OUT of (or into) the box can eliminate much of the interference.
    If the computer was sold then it meets some cert for RFI Generation, and has Metal shielding.

    It is better to fix the source of the RFI then to Fix the problems that it causes.

    Devices connected to a computer are the biggest problem for Generating and picking up RF, no question.
    .
    Last edited by KA9JLM; 04-20-2012 at 04:03 PM.
    "Theory only works perfect in a vacuum." KA9JLM Don

  10. #10
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    Make sure the case lid / door / whatever makes good bare metal contact with the rest of the case when it's whanged down, even on the industrial rack mount cases.

    Check the power supply 110v connector and make sure it's filtered. Back when I was doing OEM building for a living, we had to show DFI the "disqualified vendor department" as they suddenly stopped using potted filters/connectors, yet the power supply still had the same model and revision number. The only reason we knew is because we suddenly stopped passing our internal FCC Class A tests on our products (Yeah, it was that long ago, no DOCs.), and traced it down to that.

    If you're hellbent on getting a industrial case, these guys are pretty decent:
    http://plinkusa.net/
    [SIZE=1][B]"An armed society is a polite society. Manners are good when one may have to back up his acts with his life." - Robert A Heinlein[/B][/SIZE]

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