How to Find and Fix LED Lights That Interfere With Your VHF and AIS

Walk the boat and write down every LED light: navigation and anchor lights, steaming and spreader lights, deck and cockpit lights, underwater lights, accent strips, cabin lights, searchlights and any LED replacement bulbs in older fixtures. Note which switch or breaker controls each one. Mark the ones closest to a VHF or AIS antenna or its cable.

At the dock, switch off all lights. To keep the test clean, also turn off other electronics that can make radio noise, such as inverters, battery chargers, phone chargers and pumps. If the noise turns out to come from one of them instead of a light, that's useful to know too.

This is the test from the Coast Guard's safety alert:

1. With the LED lights off, tune your VHF to a quiet channel (the Coast Guard used channel 13 as an example).
2. Turn the squelch down until you hear background noise.
3. Turn the squelch back up just until the noise goes quiet, so it's sitting barely above the threshold.
4. Turn on the LED lights.

If the radio now opens up and you hear noise, the lights have raised the "noise floor," the background hash that weak signals have to compete with. The Coast Guard says that means both your VHF and AIS reception are probably being degraded. If the radio stays quiet, the lights you switched on aren't raising the noise floor at that radio.

A second way to see it: tune in a distant, weak but steady station, such as a far-off NOAA weather channel, and listen while a helper switches the lights on and off. If the station fades into hiss or disappears when the lights come on, you've found interference that matters. This check often catches problems the squelch test misses.

BoatUS describes a simple method with a handheld VHF that has signal bars:

• Set the squelch low enough to hear background static, at a comfortable volume.
• Hold the handheld's antenna within an inch or two of one fixture, then switch that light on.
• Watch the bars and listen. If the light is noisy, the bars rise and the static gets louder when it's on and drops when it's off. Having a helper flip the switch makes this much easier.
• Repeat on several channels. The BoatUS writer found his worst noise on channels 20 and 21; yours may be different.

On his boat, one light pushed the meter from zero to four bars. Record the result for every light.

If you have AIS, note how many targets your plotter shows at a busy time with the lights off, then switch the suspect lights on and wait a few minutes. A clear drop in targets, or targets that vanish and reappear as you switch, confirms the problem reaches your AIS too.

• No change with any light: your LEDs probably aren't the problem. Look at the antenna, cable and connectors next (see our VHF guide), or at other electronics.
• One or two lights noisy only at an inch or two, but no effect at the main radio: low priority, but keep them in mind if you move antennas or add gear.
• A light that raises the noise at your main radio or cuts AIS targets: fix it.
• Noise with everything off but the inverter or a charger on: the source is that device, not a light. Ask the maker or an electrician about filtering.

The Coast Guard found that LEDs close to VHF antennas cause the most trouble. If the noisy light sits right next to an antenna or its cable (a masthead tricolor beside the VHF whip, or an arch light beside the AIS antenna), separating them can help. That may mean moving the antenna, the light, or rerouting the light's wiring so it doesn't run alongside the antenna cable.

BoatTEST's electronics writer suggests keeping LED fixtures roughly 3 to 4 feet from VHF and AIS antennas as a working rule, and keeping LED power wires short and well away from antenna cables and electronics wiring. A quick way to tell how the noise gets in: with the noisy light on, unplug the antenna from the main radio (radio receiving only, never transmit without an antenna). If the hash disappears, it's arriving through the antenna and distance is your fix; if it stays, it may be riding in on the power wiring, so filtering (next step) is more likely to help.

Noise can reach the radio through the air or travel along the power wires. Snap-on ferrite cores fitted on the light's supply wires close to the fixture sometimes reduce it, and some LED makers sell a filter for their own fixtures. Results vary, and a ferrite is not a guaranteed fix, so retest with the handheld after each change. If the maker offers a filter, use theirs.

BoatUS recommends replacing any LED bulb or fixture that produces a strong increase in noise when it's on. Because it's hard to say exactly how much noise will hurt reception on a given boat, it suggests replacing all the noisy ones with lamps that are radio-quiet or that the maker certifies for low radio-frequency emissions in marine use. If you're not sure a product qualifies, ask the maker before you buy.

For navigation lights, replace the whole fixture with a Coast Guard-compliant LED unit rather than dropping an LED bulb into an old housing; see our navigation lights and LED upgrade guides.

After each fix, repeat the squelch test on the main radio, the weak-signal check and the AIS target count with all lights on. Do a final radio check with another boat or a nearby station at a realistic range.

The Coast Guard asked mariners who find LED interference to report it through the Coast Guard Navigation Center's contact page (choose "Maritime Telecommunications" in the topic list), with the make and model of the lights and radios and the distance between them. The NAVCEN form is open around the clock, and the center aims to answer within about 72 hours; it's for reports and questions, not emergencies. Reports help identify problem products.