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What is RFI versus QRM?

Feb 2nd 2012, 20:06


Joined: Apr 4th 1998, 00:00
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I am using the terms "RFI" and "QRM" in trying to distinguish between local generated interference (RFI) and other noise received in a receiver (QRM). The latter can be man made too, offcourse, but is more distant.
The question is, if I have a lot of noise on the band, how can I find out what it is? The assumption here is that with RFI I might be able to do something about it, with QRM it is out of my hands and I have to live with it.
Any comments?
Apr 9th 2012, 11:35


Joined: Jul 25th 2011, 14:25
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QRM is a term that is used to describe interference from another transmitter, typically another ham.

QRN is a term that is used to describe noise from lightning.

RFI ig geneally a term that is used to indicate interference from a man-made noise source other than transmitters, although it is sometimes applied to interference from unlicensed transmitters such as WiFi devices.

Ed Hare, W1RFI
May 11th 2012, 00:41


Joined: Apr 4th 1998, 00:00
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I think it all depends on the context. In simplest terms, RFI is Radio Frequency Interference. QRN and QRM are "operating terms" to describe what's happening to you at the moment. During my military days working issues in Europe, we added EMI/RFI for ElectroMagnetic Interference. The idea is that EMI doesn't have to be associated with radio, broadcasting, etc, but could also be applied to solar effects, storm noise et al.
Jun 5th 2012, 03:01


Joined: Jun 11th 2011, 06:39
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I have a puzzle about interference of some sort I'm getting. I setup this evening ready to checkin to the SCCARA Monday net but could not get through the extreme noise on the frequency at 146.985. Our 2M repeater is located at Alum Rock Park in East San Jose CA which is pretty much a straight shot from my QTH at Lexington Reservoir south of Los Gatos. Last week I had a clear signal and got along just fine. The previous 2 weeks the noise was again too severe to even hear Net Control let alone check in. The odd thing is, about 20min prior to the Net start, I heard a clear and clean signal from the USS Hornet ARC at 146.880 based in Alameda. Their repeater is located in Oakland. So it doesn't appear that I have any local RFI being generated unless it just perversely started up right at 7:30. Any ideas as to why this is happening and how to clean it up?

Steve Dowler, KJ6QXK
Dec 8th 2017, 02:48


Joined: Oct 27th 2017, 11:58
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The type of interference that I have, based on what Ralph has contributed, is some type of interference in my home. I unplugged the Wi-Fi, everything that was plugged in to my electrical strips, turned off the fluorescent light which is above station. Ralph said that the sound he provided in the file, was from a dimmer switch, which I do not have in the house at all.
I am completely stumped. The only other thing that I can figure out is that my ham shack is within 10 feet of our gas powered hot water heater...and moving the ham station, which is in my garage, is not an option. Anybody have any other suggestions?
Mar 15th 2018, 09:09


Joined: Apr 27th 2017, 16:15
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I had a lot of noise and turned things off to identify the source. The biggest culprit was a USB/120 volt plug in charger that was charging a device. I unplugged it and much of my noise problem went away.
Feb 3rd 2022, 16:15


Joined: Apr 4th 2013, 23:31
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QRM is interference in general, regardless of the source, mostly because it's rarely obvious what the source is. QRN is static, like with wall switches and atmospheric noise. Not sure where / when the "man-made" and "nature-made" thing came about, but I don't believe they are generally understood meanings of those Q-codes.

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