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@contesting.com] On Behalf
Of Jim Brown
Sent: Sunday, December 27, 2020 10:30 PM
To: rfi@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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