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Thread: RFI Shielding - Radon Mitigation Fan Motor

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  1. #1

    Default RFI Shielding - Radon Mitigation Fan Motor

    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. #2


    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. #3
    Join Date
    Jan 2000
    Commerce MI (Detroit area)


    Tell your neighbor that sparks from the bad fan can cause all the accumulated radioactive radon to blow up like a U235 bomb ! !
    73.....JD, FISTS #3853,cc 455,SKCC # 1395,tribune #12,
    Official US Taxpayer

  4. #4


    Thank you! So you are suggesting that the radon unit has a controller in it. Is that what is making the noise? It is radiating noise about 30 feet away from the unit. This is the unit that is installed.

  5. #5
    Join Date
    Mar 2009
    Los Angeles, CA


    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. #6
    Join Date
    Aug 2004
    Des Moines, IA


    Quote Originally Posted by KF6ABU View Post
    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.
    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.
    Member ARRL, SKCC #215, NAQCC #3441, FISTS #11993

  7. #7


    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. #8
    Join Date
    Nov 2004
    Western Michigan. Great summers but nasty winters.


    Does the neighbor realize the perils of EMI?
    Mark, K8MHZ

  9. #9


    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.

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

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

    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. #10


    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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