[RFI] RFI Emissions Standards for LED Drivers / Switching PS.

[Bob Turner]

The SMPS  will have 10w of its 15w capacity in use if I continue to move along with this project.   This is to replace a noisy SMPS inside a LED light housing with a LED / external PS combination.  The load cables will be long in comparison this time.  The load cables from the noisy LED are maybe two inches long and inside a metal housing.  The new load cables will be about two feet long.  I have run the SMPS with the LED and that was the test before that yielded no noise.   This time the LED load lines will be about 2 feet long.  Come to think of it the noisy SMPS/LED fixture is mounted on a horizontal metal brace that probably makes a good antenna.   This time there will be no metal brace as I'm setting up new light in a different spot and attaching to wood.  Perhaps all I had to do is move the light off of the metal support/antenna, but it's easier to setup a new one first and dismantle the old once new works.

Forget about me testing in a quiet RF environment.  I live in suburbia where the nearest house is about 15 feet away.  I have tracked down a noisy DeWalt charger on that property before.    I'll be satisfied if my noise generator SMPS noise is buried below the ambient noise.  As it is now, my existing noisy LED cannot be missed.  It takes a noise floor of 2-4 S units up to 10 over S9.  I'm glad it's my noise source as I can turn it off.

7 3  Bob
N2SCJ

-----Original Message-----
From: RFI [mailto:rfi-bounces+n2scj-lists=outlook.com at contesting.com] On Behalf Of Jim Brown
Sent: Sunday, December 27, 2020 10:30 PM
To: rfi at contesting.com
Subject: Re: [RFI] RFI Emissions Standards for LED Drivers / Switching PS.

On 12/25/2020 7:49 PM, Bob Turner wrote:
> The metal case looked promising for keeping RF inside the unit.  

Shielding (or the lack thereof) is a poor predictor of RFI performance, especially at HF. Rather, noise is coupled to wiring to the noise source and radiated by it. Likewise, RFI to victim equipment is received on wiring connected to it. In cases, coupling to/from that external wiring is the result of simple (and serious) mistakes right at the point where the external wiring is connected.

In this situation, the victim's external wiring are our intended antennas.

> So far its quiet on HF.  I have not tuned from 6m to 23cm.    The leads 
> from the source/ps to the load and LED light are 6 inches long at the 
> moment.  No noised noticed on HF with a cursory tune up the bands.

Of course it's quiet on HF -- that external wiring isn't close to being long enough to be an antenna at HF!

> Next step is longer leads to the load. 

Yes. AND to connect it to something that draws rated current with wiring long enough to be at least an electrically "short" antenna on the bands where you're listening. AND at a QTH where there's little noise from sources in your home and in the homes of your neighbors. In most cities, suburbs, and even small towns, it's common for there to be several dozen noise sources -- I live in the mountains with nearest neighbors about
500 ft from my antennas, but I often have very strong noise from homes in three different directions that clobber fairly strong signals.

My RFI tutorial has lots of detailed advice for learning whether a piece of equipment is noisy.
http://k9yc.com/KillingReceiveNoise.pdf
http://k9yc.com/KillingRXNoiseVisalia.pdf

NK7Z's website has a lot more.

73, Jim K9YC







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