[patrickbryant]

I'm not sure if this has been posted before, but for anyone who hasn't heard, several LED manufacturers are skimping on the radio frequency interference suppression in LED lights. This could wipe out your VHF and AIS reception (you can still transmit - but you may not be able to receive). That is happening frequently enough that the Coast Guard is now warning mariners about the problem.

See the USCG safety alert for details about LED interference with AIS & VHF: https://www.dco.uscg.mil/Portals/9/...INV/Alerts/1318.pdf?ver=2018-08-16-091109-630.

The USCG procedure in that alert won't work with PLL-based receivers - like Standard Horizon's because the squelch will only open with a coherent carrier - not with random noise. It's better to tune in the weakest NOAA weather station, or some other weak station, and then turn on your LEDs - one at a time. If the NOAA station vanishes or is buried in noise, you have a noisy LED. I've been in contact with the USCG people who are investigating this problem and informed them that their test procedure won't work with all comms radios. I've also reported some tests to them.

This problem is especially bad if you have a noisy LED lamp near your antenna - like a bad tri-color at the masthead. But the RFI can radiate over the supply wires throughout the boat. Installations are so variable that defined countermeasures are impractical.

A little background: it's not the LED lamps themselves that are at fault, but rather the cause is the internal pulse duration switching power supplies - intended to allow the lamps to operate over wide voltage ranges. Those of you with a radio background will know about old spark-gap transmitters. They were outlawed because they broadcast across a wide RF spectrum. Well, these defective LEDs are doing the same thing. Since the lamps are usually encapsulated, the problem isn't field repairable. The only practical fix is for the manufacturer to reduce the slew rate of the switching supplies (which will make them slightly less efficient). More time in the switch transfer range = more power dissipated as heat.

This shouldn't besmirch all LEDs. After spending hours in a Faraday cage with a spectrum analyzer, I found that some are very quiet. I tested many lamps and found the ones with the European "CE" seal were generally the best. To get that seal, the lamps have to pass a lab test for RFI. Here in the US, it's the wild west. Caveat Emptor. The worst lamps I tested were the incandescent substitutes intended to fit in the incandescent lamp housing. Most were made in China, with no RFI test certifications. But many well-known brands made in the US were also noisy.

If you're sailing an untested boat, and you can't receive a station, turn off all your LED lamps. It may solve the problem (if you don't mind being in the dark with no navigation lights).

You might try RF chokes, shielded cables, parallel bypass capacitors, etc. But some of the RFI is radiating right off the lamp housing, and you may not have any appreciable success. I tested some lamps where covering the lamp in aluminum foil - but not shielding the supply wires - eliminated nearly all the noise: so all the noise was radiating from the housing. Until someone invents transparent aluminum, that won't be a solution for a lamp.

If it radiates RFI, return it, and report the make and model to the US Coast Guard: https://www.navcen.uscg.gov/?pageName=contactUs, regardless of whether you are in the US. They will appreciate the report. They are trying to compile a list of bad lamps and makers.

73
N8QH - out

 

[patrickbryant]

Is it similar with these boat LEDs? Is it the power supply switching that's causing the interference?

Yes, it is similar, and you've given a good description of the root problem: rapid switching. In the case of marine LEDs designed for wide voltage ranges such as 10-30 volts (that's just an example range), there is a switching supply within the lamp assembly that varies its on and off duty cycle to adjust the voltage for the diodes. (I'm trying to not be too technical here - electrical engineers please forgive my brevity.) The didoes themselves do not create interference - the culprit is the internal switching supply. The rise and fall times of those switches can be only tens of nanoseconds, and that switching can produce wideband noise. Radio people traditionally call it "hash." The no-dim and wide-voltage-range "features" can (but don't have to) carry a price: noise.

There are ways to prevent that noise from being generated - there are quiet marine LED lamps available. The noisy LEDs are poorly/cheaply/carelessly designed, and possibly the design itself was never tested by the manufacturer for RFI in the VHF band. Some well-designed LEDs may also simply be defective as individual units. Until the market demands it, I doubt that any but the best manufactures test individual units for RFI. As others have noted here, the problem isn't limited to LEDs, any switching power supply can create RFI. But the problem, in general, is especially bad when you have to turn off your navigation lights to stop the interference, trading one navigation hazard (disrupted radio reception) for another (no navigation lights). Actually, what's worse is not knowing the interference is happening. The worst case scenario in my mind is a day sailor in distress, who seldom uses navigation lights, caught out at night who's not able to receive responses from the Coast Guard.

Analog power supplies could be used instead, but they would be inefficient and dissipate significant energy as heat, canceling at least some the low power consumption advantage of LEDs.