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

[Jim Brown]

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