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RFI Shielding - Radon Mitigation Fan Motor

Discussion in 'General Technical Questions and Answers' started by N3HEE, Oct 10, 2012.

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  1. N3HEE

    N3HEE Ham Member QRZ Page

    My next door neighbors radon gas mitigation system is producing high levels of RFI. Especially on the low bands! I discovered this after installing my new Hi-Z phased vertical antenna array. I have informed the neighbor and they are working on contacting the contractor who installed it to see what their options are. I would like to explore some shielding options. One idea is placing a metal or aluminum box around the entire outside unit and connecting that box to ground. Another would be to clamp on some large chokes to the ac power line feeding the unit. Has anyone had a similar experience with a fix that worked? Thanks -Joe KB3KJS
     
  2. WX7G

    WX7G Ham Member QRZ Page

    A simple solution is to change to an AC fan with no controller electronics.

    Otherwise EMI filtering is the first step before resorting to shielding.
     
  3. K8JD

    K8JD Ham Member QRZ Page

    Tell your neighbor that sparks from the bad fan can cause all the accumulated radioactive radon to blow up like a U235 bomb ! !
     
  4. N3HEE

    N3HEE Ham Member QRZ Page

  5. KF6ABU

    KF6ABU Ham Member QRZ Page

    Is radon mitigation even needed? Is this a valid, and real concern?

    With that said, putting a bunch of ferrite beads over the power cord certainly wouldnt hurt, and is pretty easy to try and test.
     
  6. AC0H

    AC0H Ham Member QRZ Page

    It's not widely reported because everybody and their politically correct mother likes to blame ALL lung cancer on smoking.
    In parts of the country where radon is a problem it causes more lung cancer than cigarettes.
     
  7. N3HEE

    N3HEE Ham Member QRZ Page

    I built a little shield out of a cardboard box lined with aluminum foil with a ground strap attached. Sniffing it with a portable AM radio the noise was almost gone! I had to put the radio right on the radon unit to hear it. Thought I had it solved, however I still had the same noise level on my HF radio on 160 meters. How is this possible? Is the noise getting to my antenna another way via the ground path perhaps? I have some #31 material clamp on chokes coming Monday.
     
  8. K8MHZ

    K8MHZ Subscriber QRZ Page

    Does the neighbor realize the perils of EMI?
     
  9. WX7G

    WX7G Ham Member QRZ Page

    The Fan RFI egress path is through the AC power wiring. RFI filtering might solve the problem.

    The easiest possible fix is to place clamp-on ferrite cores on the AC wiring at the fan. DX Engineering stocks these. Be generous with these ferrites.

    http://www.dxengineering.com/search?keyword=ferrite&dds=1


    If this does not completely solve the issue a more aggressive filter is needed. Here is a suitable filter available at Digikey.com:

    Digikey part number 603-1668-ND
    Delta EMI Group 20BAS5
    115V/230V, 20 A filter
    $12.69

    Why does this fan produce RFI? If it is a true AC motor it should not, so I suspect it is a brushless DC motor. These have electronic drivers that are RFI noisy.
     
  10. N3HEE

    N3HEE Ham Member QRZ Page

    WX7G - Thanks much! I have 5 clamp on ferrite cores coming from DX Engineering. I can clamp them right were the AC power line enters the motor housing. According the manufactures schematic it is a simple AC fan motor with a run capacitor attached to it. No hint of DC control circuitry anywhere. The radon unit is powered directly with 120VAC. Perhaps there is a DC power supply in that unit not shown on the diagram.
     
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