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Help! Furnace fan RFI killing my receiver

C

cheddarspaz2

Member
Dec 31, 2011
6
2
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Thought this was a common problem, but couldn't find any similar posts.

Each time my furnace or central air kicks on, I get a strong (S9) signal on all HF bands (mostly AM / FM modes); that wipes out most stations from being heard. I tried placing a couple ferrite cores on the AC supply source, but didn't make a difference. Possible grounding issue, antenna height or poor coax connections?

I've used the same equipment at different locations over the years and never had an issue like this. The furnace is only 2 years old, so maybe something in the fan control itself. Any ideas?
:headbang

Thanks!
 

Try putting your ferrite cores on the line going to the fan motor if you can.
Getting them closer to the source (the motor) of the noise should help.
Will it eliminate it? Probably not. But, it's worth a try.
Also, if this just started happening, it could be an indication of a problem with
the motor. I would be inclined to think that is the most likely problem, if this just
started happening and had not been going on since you started using the
AC/Heating unit.
Good luck. RFI can be tough to kill sometimes.
trucker
 
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I believe all furnace blower motors are AC induction motors without brushes or the ability to generate interference. I think it's fairly unlikely that the AC motor itself is causing the interference and probably why bypassing its wires made no difference. Most furnace issues are related to the igniter but that would not explain the problem in the AC mode.
 
It could be a variable speed motor controlled by a digital controller. My washing machine causes RFI every time the motor runs. If it is just filling up or draining no issue. As soon as the motor turns I get RFI. I can listen to the radio and hear the RFI come and go as the motor runs, stops, reverses direction, and resumes. I suspect it is from the control board and not the motor itself.
 
I am getting heavy RFI on 6 meters when the temp drops below 45 to 50*. Everyone in the neighborhood has heat pumps with "auxiliary heat strips", or resistance heaters in the 10 KW range. It does not appear to be my unit. I may have to go on a fox hunt, next time the temp drops.

Problem is, when I find it, what do I do? Not sure what would be the problem, unless one or more of the insulators is arcing over.
 
WA8ZYT said:
I am getting heavy RFI on 6 meters when the temp drops below 45 to 50*. Everyone in the neighborhood has heat pumps with "auxiliary heat strips", or resistance heaters in the 10 KW range. It does not appear to be my unit. I may have to go on a fox hunt, next time the temp drops.

Problem is, when I find it, what do I do? Not sure what would be the problem, unless one or more of the insulators is arcing over.
Click to expand...

Notify the owner that their equipment is causing interference and that said equipment is not in compliance with FCC code.
I have read that there are fixes that makers of these units have that will rectify the problem. The makers are aware of the issue they just don't install the hardware on the units. When the issue arises the local installer is sent the kit to install.

You can do a search in the RFI section at eham and get some more insight on this issue.

There is even a discussion on the Washing Machine RFI there as well.

73

Wayne C.
 
Another alternative would be to contact the manufacturer of your/their furnace, see if they have any suggestions/fixes.
- 'Doc
 
RFI Continues

The furnace motor is indeed variable speed. I have contacted both the manufacturer and the company who installed & services my new furnace. Both replied without being able to assist, stating there is no such filtering kit available and suggested I go to R.S. for a filter.

Thank you for the link to the other RFI post. I will try the remedy suggested.
 
cheddarspaz2 said:
The furnace motor is indeed variable speed. I have contacted both the manufacturer and the company who installed & services my new furnace. Both replied without being able to assist, stating there is no such filtering kit available and suggested I go to R.S. for a filter.

Thank you for the link to the other RFI post. I will try the remedy suggested.
Click to expand...


Good luck on that. Be prepared for stunned "WTF are you talking about" looks..........lots of them.

Radio Shack. You have questions, we have blank stares.
 
Email K5GP and detail your troubles and include a video clip of your interference.

Gene is very knowledgeable, friendly and always willing to help.

He's helped me out a couple times. The guy is a brainiac with RFI.

His contact info is good on QRZ.

You can also contact Mike Martin. He's also very friendly and will answer questions over the phone. Post a video link of your noise and send the link to both Gene and Mike.

http://www.rfiservices.com/
 
RFI Supression kit

What brand is your furnace? They ALL make and sell an RFI supression kit! May have to contact GE or EMERSON depending on whose motor is in your furnace. You are not the first or the only one with this problem.
There is a solution. It will take some research to find the right person who knows what you are referring to.
Good Luck!
 
Shockwave said:
I believe all furnace blower motors are AC induction motors without brushes or the ability to generate interference. I think it's fairly unlikely that the AC motor itself is causing the interference and probably why bypassing its wires made no difference. Most furnace issues are related to the igniter but that would not explain the problem in the AC mode.
Click to expand...

Thanks Shockwave. I should have thought of the DC actuator motor. After focusing on that and the fact that the un-shielded wire to the thermostat was acting as a radiator turned out to be exactly the problem. I put 11 ferrite cores on all wiring surrounding the DC motor and replaced the thermostat wire with Shielded Cat-5 and I dropped the noise from an S9 to zero. I can faintly hear the sound, but it no longer prevents reception of even the weakest signals.

It took a while to pin-point, but thanks to the help here; I finally solved the issue. For FREE!
 
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I am late to this, but I have the answer. My Trane XV-95 furnace uses an ECM motor driven by a PWM driver. Makes trash all over HF. I along with several others devised a remedy for this RFI, which I have attached here. It's all in the attached PDF.
 

Attachments

  • Trane XV95 RFI Documentation.pdf
    6.2 MB · Views: 1,255

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