Furnace Blower RFI - Suggestions?

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Sorry but the pictures that follow are gruesome and may churn the stomach of even the most stout OM or XYL...

I have a 1.5 yr old Goodman furnace that has an ECM blower motor.  In diagnosing the situation, when at the furnace and watching my waterfall, 10m gets blown out as visualized below (2nd one) the moment the relay flips and blower starts moving.  These aren't birdies they are a flock!

I am in the process of working with installer and mfg but it's not looking promising.

I have found these two articles and am headed down a path of suppressing RFI on the wires to the motor- hoping its there....  Curious if any of you have seen such a signature and have any tips as I hate to stumble around for months to sort this out - although the 10m prop is shot for a year or two more so I guess I have time....

Resolving Furnace and A/C RFI (Radio Frequency Interference) - ARRLwww.arrl.org/files/file/.../Solving%20Furnace%20and%20AC_RFI_KM4LHZ_v9.pdf



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Dave - N6XVZ

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Posted 2 weeks ago

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It's amazing how this stuff passes FCC certification? And yet when an amateur radio company wants to make a new radio or amp they put the screws to them.

Well good luck, looks like that RFI motor filter will help a lot.
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Andrew O'Brien

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Hmm, never thought about that.  I have some unsolved RFI, will keep my furnace blower in mind.

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Dave, I can't see the frequency range of the EMI on 10M, but it appears quite large.  Can you please clarify the range?  In my experience with Trane ECM units, the EMI signature is a series of perhaps 50 closely spaced pulses spread across approximately 1 KHz.  These groups of pulses are approximately 18 KHz apart and repeat over several MHz of the HF spectrum.

The attached presentation by KM4LHZ is EXCELLENT and mirrors my experience in virtually every way.  Be careful to explore ALL the wires that exit the metal enclosures as they can easily be antennas conducting the EMI to the outside world..  If you happen to have motors manufactured by Regal Beloit, you are fortunate.  The engineering staff was very supportive five+ years ago when I encountered problems with their motors. 

I suggest you follow the analysis and resolution recommendations in the paper and report your progress, good or bad, so readers here may offer their experience.
Chuck, AE4CW
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Dave - N6XVZ

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Appx 24.8 to 31.8 MHz. So 7mhz. Huge. Peaks every 15 kHz. It seems like such a large range vs what others including you mention seeing.

I do have to ferret out the motor mfg. one can hope it is the same mfg.

Really the only wires exiting the enclosure are Thermostats and power. But will keep them in suspicion.
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I have seen the EMI extend 7 MHz and more.  The peaks from the EMI emitting motors consists of clusters of many very narrow pulses (~50) spanning approximately 1 KHz.  And, these pulse group repeated approximately every 18 KHz over many MHz.  The noise signature I see in your photo above is different from anything I have seen coming from my HVAC motors.
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Dave, Have you looked at whole house AC filters  something like the Morgan 330 units, http://www.surgestop.com/surge-products/m-330.html  . I think someone else now builds there products - I have a few of the 400 series and they seem to work at taking out or reducing  issues I have had. and will probably add the 330 as well.
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Larry - W8LLL

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My washer/dryer combo did this until i put some mix 31 snap ons on the 240vac power cable right up to the back panel. This prevents the motor that is emmitting rfi to use the power cable as an antenna and transmit it farther and stronger.
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Mark Aaker K6UFO

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When my new furnace had this problem several years ago, the following steps helped.
The manufacturer had a "RFI kit" available to installers, and it was basically just an 
AC line filter. It helped. I then used a small loop as an antenna "sniffer" as I tried to 
see where the noise was coming from, even taking the front panel off. The motor wires 
were the worst, so I replaced them with a "twisted pair" with a small ferrite at each 
end and the noise was reduced to negligible levels at my antennas.
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Ed Johnson

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I had the same problem.. Popped open the inside unit and installed 10 split ferrites Mix 31 on all wiring harnesses that I could get to..... including wires to thermostat (great antenna).  Problem is history.
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Andy - KU7T

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Same issue here, although the spectrum looks different. I am still trying to get my Trane service company to actually understand what I am talking about. :-(
Anway, here is how my Heatpumps look like on 20 and 15