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Author Topic: RFI From Treadmill  (Read 4460 times)
KB1WSY
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Posts: 777




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« on: February 13, 2014, 03:47:14 AM »

My landlord, who lives in the apartment above mine, has built an exercise room in the basement.

When he is using his treadmill, there is broadband loud "whirring" sound all over the bands. It sounds pretty much exactly like the treadmill itself: a rhythmical "whirr, whirr, whirr" that speeds up when the treadmill speeds up. This affects not only HF ham bands but also the entire AM BCB spectrum.

A while back AB9TX had a thread here about RFI from a neighbor's treadmill (see http://www.eham.net/ehamforum/smf/index.php/topic,87174.15.html). His case was rather different though: it was a constant common-mode noise 24/7 even when the treadmill was switched on, but not actually being used. In my case, there is no noise at all except when the landlord and his wife are exercising -- they are very fit and this is quite frequent!

AB9TX said he was able to lower the noise by about 3dB with a surge-suppressor power strip on the treadmill. Well, in my case, a 3dB drop wouldn't be anything like enough attenuation. In his case, the treadmill was in the house next door, in my case it's only about 20 feet away in the basement.

I'm very friendly with my landlord (and he is a QRT ham) but before I bring up the issue with him, what do you think my first experiment should be, at that point? Ferrite beads on the power cord?

73 de Martin, KB1WSY
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K1CJS
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« Reply #1 on: February 13, 2014, 05:47:12 AM »

Just an off the cuff answer, but how about simply speaking to him about it?  Being a former ham, he probably would be more receptive, you may draw him back into the hobby by involving him, and you may get the noise cleared up quicker.  

On the other hand, the treadmill may need some maintenance--if he uses it all that much, and your involving him may let him see that just because of the amount of noise being generated.  Since it's better to kill the noise at its source...

Just mention it to him--"By the way, I know when you're using your treadmill because I can hear hash on my ham equipment when you do."  Make it friendly and undemanding.  Chances are he'll realize something may be going bad on the treadmill itself.

« Last Edit: February 13, 2014, 05:49:22 AM by K1CJS » Logged
KB1WSY
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Posts: 777




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« Reply #2 on: February 13, 2014, 06:55:07 AM »

Just an off the cuff answer, but how about simply speaking to him about it?

Indeed I will be discussing it soon because there are also some rebuilding issues with my shack. I want to board up some of the shack windows, in a reversible way, and I'm fairly sure he will give permission. The shack is in a little-used storeroom at the back of the house and he's already boarded up some of the other windows in it. He's a cool landlord: he's also given permission to put up a full-size dipole in the yard.

That aside, the main reason I started this thread was to do some research in advance so that we would know "what to try first" in terms of quenching the treadmill noise. It's a new treadmill -- well, about a year old, but I noticed the noise immediately it was installed, when it was new. Until now it's not been a big deal because I'm in "SWL mode" while building my "real ham shack" but it would be a real PITA if it started in the middle of a real QSO; it makes reception impossible.

I figured the first thing to try would be ferrite beads (chokes) in the AC cord ... so I could get hold of some of those in advance ... unless the experts here think that would be a blind alley.

BTW my landlord has an engineering degree from MIT, but he's been in software engineering for most of his career. As a ham, he's been QRT for decades, but says he still remembers Morse code.

73 de Martin, KB1WSY
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WX7G
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« Reply #3 on: February 13, 2014, 06:58:17 AM »

To fix this my first try would be to place type 31 ferrite snap-on cores on the power cord. The DXE-CSB-275P kit is suitable if the AC line cord will fit through the 0.275" core. Two or three kits may be needed.

    http://www.dxengineering.com/parts/dxe-csb-275p


If this does not yield enough attenuation, and there is room inside the unit, installing a filter such as the Delta 20DRGS5 is worth a try.

    http://www.digikey.com/product-detail/en/20DRGS5/603-1263-ND/2560387
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KB1WSY
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« Reply #4 on: February 13, 2014, 07:18:39 AM »

To fix this my first try would be to place type 31 ferrite snap-on cores on the power cord. The DXE-CSB-275P kit is suitable if the AC line cord will fit through the 0.275" core. Two or three kits may be needed.

    http://www.dxengineering.com/parts/dxe-csb-275p

Excellent. I've ordered the cores. They come in sets of 10, which is useful because I can also use them on other appliances in the future if needed. There is a cheaply made closet-style freezer in my kitchen, about 15 feet from the shack, that I also suspect of RFI.

If that doesn't work we'll try the filter....

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K5LXP
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« Reply #5 on: February 13, 2014, 08:11:16 AM »

Another factor in mitigating RFI is increased separation between the emitter from the receiver.

You mentioned he has given you permission to put up a backyard dipole, but you didn't say if that's what you were using.  You did say you were just SWL for now while building the shack so that may mean you're using a basic random antenna.

If your antenna is effectively near the treadmill it won't take a lot of RFI to cause problems.  If you're antenna is well isolated and far away from the treadmill, you may find you can't hear it at all.

Ferrites can't hurt so you might as well try it, but consider your antenna as well.


Mark K5LXP
Albuquerque, NM
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KB1WSY
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Posts: 777




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« Reply #6 on: February 13, 2014, 08:44:35 AM »

You mentioned he has given you permission to put up a backyard dipole, but you didn't say if that's what you were using.  You did say you were just SWL for now while building the shack so that may mean you're using a basic random antenna.

I am indeed just using a long-wire antenna strung in the trees, with the ground side of the receiver connected to a cast-iron heating radiator. The antenna wire comes into the shack unshielded. Probably the worst possible setup in terms of noise pickup.

The dipole will be coax-fed with the center point at 30 feet up and the feedline coming straight down, then into the shack. I am hoping for a noticeable decrease in noise, compared to the wire antenna. Will be putting up the dipole when the weather improves ... today, yet another snowstorm....

73 de Martin, KB1WSY
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K1CJS
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« Reply #7 on: February 13, 2014, 08:55:45 AM »

As I said in my first post, any mitigation should be on the power lines as close to the noise producing device as is possible.  Also, depending on the type motor on the treadmill, the cause of the problem may be in the treadmill control or even in the motor itself.  Could be that the treadmill--and the freezer unit--may be needing service in the near future.  Good luck and 73!
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KD0REQ
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« Reply #8 on: February 13, 2014, 01:25:56 PM »

most good-quality and up treadmills use DC brush motors.  some smaller suppression capacitors at the motor leads (.005) and ferrite beads might help lots.  they're probably going to be driven with pulses so put ferrite at the control head, too.

there is also the possibility that the belt is generating enough static that its random discharge may be causing a short-range static signal.  a quick test might be getting a screen door spring, bolt one side under a frame bolt someplace, and drag the rest lightly over the belt back by the "fling you off, dude" end with a string.
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