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Re: [CQ-Contest] LED Lighting RFI

To: cq-contest@contesting.com
Subject: Re: [CQ-Contest] LED Lighting RFI
From: K9MA <k9ma@sdellington.us>
Date: Thu, 19 Oct 2017 20:11:09 -0500
List-post: <mailto:cq-contest@contesting.com>
The "AM radio up close" test may or may not tell you whether the device produces enough RFI to be detectable at HF.  A better test is to listen to your HF radio, using your normal antennas, as you switch the device on and off. It's almost imperative to use a spectrum display with at least a 100 kHz span, as the switching supplies in these devices typically run at 20 kHz and up, generating harmonics.  If your receiver happens to be tuned between harmonics, you won't hear it, but it's guaranteed to drift right to the frequency of that rare DX you're trying to work.

I was successful in tracking down a noisy switching supply with a portable HF receiver.  After it warmed up, this source was quite stable, I could tune a portable HF receiver to a harmonic on 20 meters, which I could hear on the station receiver.  I walked around the neighborhood until I found the strongest signal, then went home and got my 135 MHz tracker, with which I could hear it standing right in front of the neighbor's house.  In fact, it pointed to the right room in the house.  I went in with the portable 20 meter receiver and asked them to start switching lights off.  It was the power supply for the LED tapes in the family room.  I offered to pay half the cost of a replacement supply, and all is well.  (At least from those lights; there are many more noisy switching supplies in the neighborhood.)


Scott K9MA

On 10/19/2017 16:13, Mike Ritz wrote:
I have a variety, but the one that I have easiest access to for checking was marked as 
"MaxLED by Maxlite, 800 lumens, 2700K, 9W". I could put the AM radio within a 
few inches of the lamp and there was no noticeable noise. That said, this is a more 
expensive dimmable LED bulb, and I did find out that the dimmer switch itself (the lamp 
is from IKEA), puts out quite a bit of noise unless the LED lamp is driven to full 
brightness. I guess this could be expected as it probably pulse width modulates the lamp 
to provide the dimming.

Around my radio benches are pretty quiet, as all my supplies for 12V equipment 
are transformer units, mostly from the local Goodwill store (generally $2.99 
each!). A lot of hash is noticeable around the Comcast router in adjoining 
room, but my question is; How far out does the noise have to go to be a 
problem? If I only can detect the noise with my AM radio at 6 inches to 1 foot 
or so from the object, is that quiet enough, or is ANY noise emitted to any 
distance unacceptable? How far do we need to take it, and how much noise is 


----- Original Message -----

From: "W3IDT Bob" <w3idt@comcast.net>
To: "Mike Ritz" <w7vo@comcast.net>
Sent: Thursday, October 19, 2017 9:29:29 AM
Subject: Re: [CQ-Contest] LED Lighting RFI


You said, "Surprisingly, the LED bulbs I have in all my lighting
fixtures have been quiet."

Do you know what brand?


Bob, w3idt

Scott  K9MA


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