[CQ-Contest] LED Lighting RFI

[K9MA]

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.)

73,

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 acceptable?
>
> 73;
> Mike
> W7VO
>
> ----- Original Message -----
>
> From: "W3IDT Bob" <w3idt at comcast.net>
> To: "Mike Ritz" <w7vo at comcast.net>
> Sent: Thursday, October 19, 2017 9:29:29 AM
> Subject: Re: [CQ-Contest] LED Lighting RFI
>
> Mike,
>
> You said, "Surprisingly, the LED bulbs I have in all my lighting
> fixtures have been quiet."
>
> Do you know what brand?
>
> Thanks.
>
> Bob, w3idt


-- 
Scott  K9MA

k9ma at sdellington.us