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Old 02-08-2019, 11:45 AM   #1
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LED Interference

I had a LED flood light that interfered with the VHF and FM radio. So I did some research and found Marinebeam.com. On their website's FAQ section they have an article "Controlling EMI" describinh their commitment to selling light that don't emit EMI or at least emit very low levels. That sounded good so I ordered a small flood light. I installed the new light and found that while the interference was less it was still there. I'll admit that my small interior FM antenna was a few inches away on the other side of a bulkhead. Yesterday I spent time moving the FM antenna about 4' away and the interference was gone until I changed the station and there it was as bad as ever. My vhf antenna cable passes about three feet from the light and the actual antenna is 8' away from the light. I am working on rerouting the vhf antenna cable to see if that makes a difference.
Anyway Marinbeam did reply to an email:

"That is a very common lamp that we have not had issue with. While we test all of our products for EMI and ensure that they have low output, it is also inherently part of electronic devices. How far is this lamp from your antenna or cable and do you have coils in the cable? These factors are important in ensuring that even low EMI fixtures are not amplified to cause a problem in communication."

I have many other LED lights on the boat some as close as the new light that don't cause problems.
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Old 02-08-2019, 12:32 PM   #2
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Yes. We have found interference occurs when our cabin LED lights are on and we have been told that it is also severe for those who receive our VHF broadcasts, so we switch them off when traveling unless required. The points you make make about your exterior LED spotlight make me concerned about interference with our LED running lights. I will look into this.

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Old 02-10-2019, 10:00 AM   #3
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The US Coast Guard on this subject:

https://www.dco.uscg.mil/Portals/9/D...-16-091109-630

A vendor at the Vancouver boat show indicated there is a filter that can be installed on the power wires to the VHF. This should be done as near as possible to the radio. I have no idea if this works, but Iím going to source this filter and see if it works.

Jim
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Old 02-10-2019, 10:36 AM   #4
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If you have access to the LED power wire, I have some effective ferrite sleeves that are made to target VHF frequencies. PM me if interested. I bought a bunch at some discount.
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Old 02-10-2019, 01:23 PM   #5
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The interference caused by LED lights is generated in the high efficiency power supplies. Low power lights using only resistors do not produce interference but also don't have the efficiency. I don't know about the interference on transmit, but on receive it is the 455Khz intermediate frequency used by the radio's tuner that is primarily affected, and the proximity of the light to the radio is of much more effect than proximity to the antenna & cable. We need manufacturers to apply more design effort into suppression. I plan to do some tests with power line filters and will post any useful results.

I recently did a commercial installation with Perko 210 series navigation lights. While they were not interference free, it was barely detectable when the lights were 5 ft or more away from the radio. Placement directly beside the antenna did not affect interference.
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Old 02-10-2019, 01:32 PM   #6
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I haven't had a chance to dig into it further, to see what frequencies might be involved, but when I was using a tone probe the other day I noticed some old DRSA dimmers (intended for incandescents) caused a tremendous amount of noise that the probe picked up. This being with some MarineBeam LEDs. Now, the same LEDs in a circuit that was just switched on/off produced none of the same RF noise.

So, yeah, LEDs and RF noise can be a thing, and it's worth making sure you're not losing VHF as a result. But understand that it might not be just the bulb alone if you have dimmers onboard.
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Old 02-10-2019, 01:34 PM   #7
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A noise filter of some kind would interesting to try. I see two options mentioned one is a filter on the radio and another on the light. Perhaps both? It is also interesting that maybe the interference is directly to the radio not the antenna/coax. The quote from Marinebeam in my original post seems to implicate the coax.
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Old 02-10-2019, 01:56 PM   #8
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Dimmers work the same way, by pulsing the current on and off at a high frequency. These circuits produce harmonics - multiples of the operating frequency, and the harmonics cause the interference. The power circuit provides a path which can be suppressed with inline filters and this may do the trick in some cases. Connecting the radio's RF ground directly to the main Neg buss may also help.
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Old 02-10-2019, 02:02 PM   #9
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No, in my case it's the dimmers. They're not designed for LEDs. It's on my 'to do' list to replace them (Anigmo makes one I'm going to try).

Tangentially to this I have a house with Lutron automated lighting. Lutron being the folks that inventing the lighting dimmer. I've been to the their paid training, and those folks KNOW what the're talking about. I'm VERY familiar with issues with LEDs and dimmers. LEDs are not just drop-in replacements for incandescent bulbs, and some LEDs are flat-out incapable of being dimmed properly.

So it came as no surprise to me that the on-board dimmers that 'worked' with incandescents weren't going to work properly with LEDs. I was just surprised to hear the RF noise they caused, that the tone probe picked up. I'm looking forward to having time closer to Spring to see about replacing the DRSA dimmers.
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Old 02-10-2019, 02:19 PM   #10
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I think the very low current draw of the LED lamps causes the dimmer to be operating with extremely short pulses which produce stronger harmonics.
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Old 02-10-2019, 02:26 PM   #11
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No, the noise is because the DRSA dimmer doesn't isolate the -/+ of the bulb from the boat ground. Modern dimmers isolate the -/+ of the light separate from the boat ground. But that wasn't how they're wired up. The challenge is finding where the ground for the lights is brought together and separating it out for to properly used the PWM -/+ part of a modern 12v dimmer. I've managed to get into enough of the panels to find where that happens, so next it's just a matter of re-wiring and installing a new dimmer. I'm reasonably confident that will solve the problem. Because when using these same bulbs WITHOUT the old dimmers they don't make the same RF noise.

Noise, I'll add, that is only being picked up by the tone probe. Last Summer I did the tests the USCG recommended and did not detect any problems. So the noise I'm picking up is, apparently, not presenting problems for marine VHF channels. Not all RF noise is the same same.
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Old 02-10-2019, 02:36 PM   #12
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Interesting discussion! I will try the recommended fix to the VHF power supply and report back. It might be that this intended fix DOES NOT work, in which case itís back to square one.
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Old 02-10-2019, 03:45 PM   #13
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The tone probe will not pick up the harmonics in the RF range, only the operating frequency which is typically in the high audio range, around 20Khz, and maybe the 1st harmonic (2x), but you would not be able to hear that.
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Old 02-11-2019, 07:58 PM   #14
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I routed my vhf antenna cable away from the offending light and the interference went away.
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Old 02-19-2019, 05:13 PM   #15
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Any LED lighting that uses voltage modulation (pulses the power on and off) has the potential to cause interference at radio frequencies. If you're doing a conversion I would look for kits that don't use PWM power supplies. We installed these in every dome fixture on the boat https://www.doctorled.com/p73.htm with no issues.
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