Radio Interference From LED Lights

[k0ua]

I put a couple ferite cores on my LED light bars & radio power wires. It helped a bit on one (the least noisy one to start with), but not much on others.

It can't hurt to try, but don't count on it. Read up on HAM radio & RFI, it can be an insanely deep subject. I have my HAM radio extra license & still only get a bit of it.

Keep in mind there are several factors not stated in these scenario's. What is the mix of the snap on ferrites and what is the frequency of interest? Ferrites come in "mixes". Mix 28 to mix 61 are common mixes of ferrites used for these purposes. with the lower numbers more effective at lower frequencies and the higher numbers more effective at higher frequencies. In other words, if you have a problem with interference with your weather radio at a frequency at 162 Mhz you would be more interested in obtaining a mix 61 ferrite. But wait there is more!. When you snap on a ferrite over a wire, the closer the ferrite is to the wire, in other words the tighter the fit, the more effective it is. But wait there is more! If you can put multiple turns thru the ferrite, the effectiveness increases by the square of the number of turns. In other words, two turns thru the ferrite is 4 times as effective. But wait there is more!. The stinking cheap snap on ferrites that come from China, rarely ever tell you what mix they are. It is the luck of the draw, you don't know what you are going to get.. Also closed torroid ferrites are very much more effective if you can get the ends of the wire wrapped thru them. So they are not as convenient to use. But they are way more effective.

 

[k0ua]

Also don't forget about the efficiency of using bypass capacitors of the proper voltage rating and type to suppress RFI emissions from devices. Of course this requires opening up and soldering in a capacitor at the proper location. This is probably beyond the experience level of most users.

 

[Fallon]

Keep in mind there are several factors not stated in these scenario's. What is the mix of the snap on ferrites and what is the frequency of interest? Ferrites come in "mixes". Mix 28 to mix 61 are common mixes of ferrites used for these purposes. with the lower numbers more effective at lower frequencies and the higher numbers more effective at higher frequencies. In other words, if you have a problem with interference with your weather radio at a frequency at 162 Mhz you would be more interested in obtaining a mix 61 ferrite. But wait there is more!. When you snap on a ferrite over a wire, the closer the ferrite is to the wire, in other words the tighter the fit, the more effective it is. But wait there is more! If you can put multiple turns thru the ferrite, the effectiveness increases by the square of the number of turns. In other words, two turns thru the ferrite is 4 times as effective. But wait there is more!. The stinking cheap snap on ferrites that come from China, rarely ever tell you what mix they are. It is the luck of the draw, you don't know what you are going to get.. Also closed torroid ferrites are very much more effective if you can get the ends of the wire wrapped thru them. So they are not as convenient to use. But they are way more effective.

I'm aware of this. I got the mix that targeted close to FM frequencies (don't remember the number offhand). All clip on ferites had 2 wraps through them. I had 1 snap on & 1 toroid on each wire. I did my due diligence, at least a few hours of research. Like I said, deep rabithole to go down.

 

[DieselBound]

Not that this is going to help the OP, but I've read that CREE LEDs tend to not cause RF problems. I don't have any, so I am unable to vouch.

 

[Fallon]

Not that this is going to help the OP, but I've read that CREE LEDs tend to not cause RF problems. I don't have any, so I am unable to vouch.

LEDs don't cause any interference at all, even low quality ones. It's ALWAYS the power supply. The nature of how the power supplies work cause the RFI.

Cree does make some of the higher quality LEDs though.

 

[DieselBound]

Is it, then, the power supplies that are used for CREE lights? Is there a special pairing, or can anyone use crappy power supplies on CREE lights as well?

 

[vvanders]

Is it, then, the power supplies that are used for CREE lights? Is there a special pairing, or can anyone use crappy power supplies on CREE lights as well?

LEDs are pretty tolerant of any power supply as long it doesn't go overvoltage. The problem with cheap power supplies is they aren't designed right and don't use the correct filtering.

A switched mode power supply looks a lot like a radio transmitter. They charge up a bunch of current and dump it, usually at a fixed frequency. If you get a wire(AKA antenna) that's resonant at that frequency, boom you've got a component that's throwing off a ton of RF hash.

The best thing you can do is buy name-brand products that have gone through proper RFI testing. Usually when you buy cheaper power supplies the first thing they skimp on is the filtering.

 

[crazyal]

If it's just AM/FM causing an issue then I would try a filter for the antenna. Maybe the RF isn't in the 12v power line so adding ferrite beads aren't working because that's not where the problem is. Should be about $10. Plus (I think someone else pointed it out) you can always add a capacitor from the power lead to ground. It'll look like a battery until charged to DC then it'll have no effect where as AC will pass through it.

 

[vvanders]

A filter at the antenna probably isn't going to help much, all modern radios have pretty strong passband filters either at the IF frequency or in the front-end if they're direct conversion. If you're picking up things it's because that frequency is present in your RF environment.

Filter capacitors are only going to help if they're on the power supply output rather than input and the sizing is pretty important. Any resonance needs to be tuned to the proper RC/LC circuit that can also pass the amount of current required.

Really the best option if you have RF problems is to use ferrite cores since they don't require a circuit connection or you can shield the whole component in an enclosure.

 

[Jack1940H]

I am not familar with RF issues relative to LED's. A tyical LED is driven with a DC voltage source. The diode usually will excite (emit light) at around 3vdc-4vdc and perform at peak outut at arround 5 - 18vdc. If the LED is powered by an AC source it will have a built in transformer driver circuit that converts the 120vac line source to 12vdc. This might be where the rf is being generated and if so I have no idea of how to suppress it.