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

    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

    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

    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

  5. KF6ABU

    KF6ABU Ham Member

    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 Premium Subscriber

    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

    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 Ham Member

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

    WX7G Ham Member

    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

    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.
     
  11. AJ8MH

    AJ8MH XML Subscriber

  12. N3HEE

    N3HEE Ham Member

    Interesting! I placed 3 large .5 inch diameter #31 material clamp on ferrite chokes on the AC power line with no luck. Still just as loud. RadonAway and contractor that installed it are not helping.
     
  13. WX7G

    WX7G Ham Member

    Are you sure it's the RadonAway? Have you powered it OFF at the motor to confirm that it is the source of the RF noise?
     
  14. N3HEE

    N3HEE Ham Member

    PROBLEM SOLVED! I powered the radon unit off at the motor and the noise was still there. I spent an hour in the neighbors house tonight with AM radio in hand. Sure enough it was the wall wart for their cable modem. It was attached to the same AC circuit as the radon unit and using the house wiring for a antenna. Thanks for all of your help everyone.
     
  15. WX7G

    WX7G Ham Member

    Is it the wall wart or is it the cable modem?

    If it is the wall wart the RF noise will occur at harmonics of the switching power supply and will not be continuous across any band. If it is continuous across a band it is the cable modem.
     
  16. K8AC

    K8AC Ham Member


    I have a similar situation in a summer home in the Blue Ridge Mountains. I've not had the time to pursue the problem yet, but here's some info: These fans are unique in the construction of their housing - here's a link showing some detail: http://www.capitalregionradon.com/info . In case of a failure, the entire sealed housing and motor must be replaced. It seems that all the fans are powered from 120V AC and the literature from some manufacturers shows a start capacitor in the circuit but they never give details about the motor. The fans run 24/7 at a constant speed. Looking at the photos, there may be room in the box for ferrites or even one of the filters mentioned. The RFI that I hear sounds just like what you hear from a light dimmer when listening to the AM broadcast band.

    What would be the advantage to a brushless DC motor design over an AC motor? I suspect that it would be cheaper (save the cost of the start capacitor?), or they'd just use an AC motor.

    To those who question the need for radon mitigation: Depending on the geological characteristics of the ground where you live, you may have a high radon occurrence or none at all. Here in the eastern mountains, radon appears in many home basements, apparently due to the type of rock prevalent here. Today, when you sell a home here, it's very common for the buyer to insist on a radon test and I understand that some banks won't make mortgage loans unless that is addressed. A properly certified home inspector uses an instrument that's left in the basement for 2-3 days and measures the radon concentration. You can also buy test kits you use yourself, but you have to send in the detector and have it analyzed by a lab. If radon is found to be at a level beyond the recommended minimum, mitigation is required. Again, there's no room for belief or disbelief here - if you want to sell a home, you have to do the mitigation. That usually consists of drilling a 4" hole in your concrete basement floor (sometimes 2 holes) and routing 4" PVC pipe from those holes to the outside of the home where the fan is mounted. The fan creates a negative pressure under the concrete floor and thus removes most of the radon gas. The output of the fan is exhausted near the peak or eaves of the roof where it dissipates into the air. The fan is pretty quiet sonically, and runs 24/7 from a 120V line. After the mitigation system is in place, the installer tests the radon level again to make sure it's below the maximum allowed. In our area, specially trained contractors charge from $1,200 to $1,600 for a complete installation. The installer has no idea what RFI is, and doesn't care.

    73, Floyd - K8AC
     
  17. WX7G

    WX7G Ham Member

    K8AC,
    it turns out the motor is an AC motor and exhibits no RFI. The RFI is from a modem or a modem power supply on the same AC circuit.
     
  18. KF5FEI

    KF5FEI Ham Member

    Looks like an industrial-grade poop fan system.

    Just out of curiosity, what parts of the country are susceptible to radon seeping from the soil?
     
  19. WX7G

    WX7G Ham Member

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