Disputed interference between LED masthead light and VHF antenna

[Lake-Effect]

Originally Posted by team karst

THis is a job for mix 61 ferrite on the leads. I"m an EMC engineer, btw. Optimally, the design is solid, so, its not and likely many are not. Unlikely the "bulb" itself is radiating much, its too small. Its much more likely to be the wires. Yes, the legal spec is not good enough if the culprit and victims are within 10 feet or so.

Excellent! is this your prescription then for the typical "noisy" marine LED? Could you give us a link to a source for suitable ferrites?

Modern boats are a minefield of EMC issues. I have one.... still working the solar controller messing with my airband (am) radio. stubborn.

Interference is a real bummer. Listening to the HF band is nearly impossible in the city. Not that there's much worth listening to anymore...

[billgewater]

Back in the "un-enlightened" pre LED days I used filament bulbs in my Tri-colour mast head light. There was no apparent interference with the TV or any radio.
The plastic started to lose transparency so I replaced the complete assembly with a new fitting with LED bulbs. The TV antenna is also at the mast head and the interference is now such that the TV screen just goes blank when the tri-colour is on. This is tolerated as we usually aren't watching TV when sailing at night - might watch a DVD. All the radios suffer from interference when the tri-colour is on.

I understand that we use the LED's because of their longevity and relatively low power consumption and I guess you just need to weigh it all up. I suspect that there may be LEDs that don't have this PWM chopping process but I have learnt to live with the current (sic) problem.
I recently pulled apart all 10 of my interior 12 VDC fluorescent lights and put LED strip lighting in. I just removed the complete circuitry for the flouro lights and connected the LED strips to the rocker switch on the light casing. These lights are really bright and you can choose which LED strip e.g. white/bright/amber etc. However, it seems these super cheap LED strips do not produce any apparent RF interference at all, so surely there must be equivalent LEDs useable for a tri-colour etc. (Admittedly, these lights are inside whereas the TV antenna is remote at the mast head).
I reckon that trying to supress the RF at the masthead lights is a waste of time as the power supply cables will also transmit RF if the LED circuits are producing PWM outputs. Could be wrong.
Also, most individual LEDs are small, and flat. They transmit light only away from each flat surface but not in all directions like a filament bulb does. That may be why the LEDs used usually have lots of smaller LEDs around a cylinder shape (festoon?) to create a 360 degree light transmission. The temptation to install a PWM power saving system inside the cylinder is probably just too much.

[team karst]

https://www.digikey.com/en/products/...QAEqLi8Amy4nUA

Do NOT buy unknown material from Amazon, etc. Mix 61 works well from 100MHz to around 300MHz. Snap ons do not require cable removal. Find a size that will take two turns around of the LED feed wire. Do NOT exceed 3 turns for VHF suppression. IT might take 2 or 3 cores, depending how bad the LED driver design is. Let us know how it goes; sounds like bosun chair time.


While I'm thinking about it, my 12V USB panel mount charger took a mix 61 to settle down too.

[Tehani]

This is a complete (AND very small) EMI filter:

https://www.mouser.com/ProductDetail...6ub4HRRQ%3D%3D

This one is easier to solder:

https://www.mouser.com/ProductDetail...qI66B3sg%3D%3D

Mount it just before the led bulb inside the light housing, and protected with neoprene tape.

[Jammer]

Originally Posted by Lake-Effect

..., I think you'll find that most marine LEDs have a PWM frequency already under 1 MHz. The problem is that these are usually square or rectangular waves, which have tons of higher harmonics, and its the harmonics that are the usual source of RF interference. So the fix is good design that includes suppression of the higher harmonics, which only has marginal impact on efficiency.
...

I agree with all this

Originally Posted by team karst

THis is a job for mix 61 ferrite on the leads. I"m an EMC engineer, btw. Optimally, the design is solid, so, its not and likely many are not. Unlikely the "bulb" itself is radiating much, its too small. Its much more likely to be the wires. Yes, the legal spec is not good enough if the culprit and victims are within 10 feet or so.

I agree with all this too

Originally Posted by Lake-Effect

Excellent! is this your prescription then for the typical "noisy" marine LED? Could you give us a link to a source for suitable ferrites?

As already posted upthread, Digi-key is a trustworthy source with reasonable prices and rapid fulfillment. Material 61 ferrites are available in many size and shapes, choose what works for your situation.


Usually a combination of ferrites and bypass capacitors works best. It is best to work out the correct combination experimentally. Components that are excessively large are hard to mount and may affect the performance of the LED. Unfortunately, that makes it a science project rather than something simple and cookbook.


Another good alternative is to move the lighting down the mast. There are threads elsewhere on this. There are many sailors who prefer an anchor light that is lower on the mast, and who utilize navigation lights near deck level rather than a tricolor, for reasons other than RF interference. Another combination to consider is a red-over-green light stack with the upper red light near, but not at, the top of the mast -- plus deck-mounted nav lights.

[Tehani]

Originally Posted by Tehani

This is a complete (AND very small) EMI filter:

https://www.mouser.com/ProductDetail...6ub4HRRQ%3D%3D

This one is easier to solder:

https://www.mouser.com/ProductDetail...qI66B3sg%3D%3D

Mount it just before the led bulb inside the light housing, and protected with neoprene tape.

2 units are required, one for the tri-color light and one for the anchor light.

This removes conducted EMIs more efficiently than a single ferrite or capacitor. The mast cables are antennas for these high-frequency currents and transform them into induced EMI, so these devices must be installed right at the point where they occur (right at the connections of the LEDs).

[ahun]

Thanks, I will try the filters once we get to an area where I can obtain them. Don't want to invest too much into the whole thing, the AIS and radio are more important to function than the lights. I can substitute the navigation lights anyway.

The other problem is, the housing of the masthead light is tiny, I am not sure if can fit anything inside by the side of the bulb.

[team karst]

Originally Posted by ahun

...



The other problem is, the housing of the masthead light is tiny, I am not sure if can fit anything inside by the side of the bulb.

The initial try would be to wrap the 12V wiring, near the fixture, with the ferrite.

True, board level fixes are usually the proper way to fix EMC issues. But, you are talking now about PCB designs; Saying that, its usually possible to install bypass caps, if you are careful. If the ferrite doesn't work well enough, consider a different LED.

That Murata part looks good for performance, but note the 1.3mm pad sizes. Maybe tough for many to attempt soldering.

[Lake-Effect]

It's still disappointing that a LED masthead tricolour, intended for use beside the VHF antenna, would not be properly designed for that situation.

[team karst]

Originally Posted by Lake-Effect

It's still disappointing that a LED masthead tricolour, intended for use beside the VHF antenna, would not be properly designed for that situation.

Exasperated by running the radio coax and 12v lamp wires in parallel for 50 feet[emoji30]

Just found the leaded Murata cube. That looks nice! I’ve found Murata, Wurth, and Fairite my fav providers.

[wholybee]

I have to disagree on the filters or shielding of wires doing anything at all. Go ahead and try, but I doubt anything will work except a different bulb.

The issue is that an LED is a diode. If you modulate a signal into a diode, you have a transmitter. In a very literal sense, as that is how transmitters are actually built, with a diode. So if a PWM driver is used, you have a transmitter, with the bulb itself as the antenna. No amount of shielding or ferrites on the wires will change that. Worse, PWM is a square wave not a sine wave, which creates harmonics that affect the entire spectrum, not just the single frequency of the square wave.

To the OP, Try a bulb or fixture that others know work. I use Dr LED bulbs and they work well for me. Sometimes, not always, I can hear the tone of noise change if squelch is off. It doesn't increase noise, and doesn't ever break squelch or affect my reception. If that works, present that to the mfgr of yours and ask for a refund.

[wholybee]

Originally Posted by ShawnMack

I have a dumb question because I know there are some super smart EE folks on here.
I understand that they design the PWM circuit to cycle as fast as possible primarily for efficiency, I think. Could you not turn the frequency down to simply accept a lower overall efficiency but also not be as close to the radio spectrums we rely on? Or is the EMF just so powerful its specific frequency is irrelevant?

The issue is that is is a square wave. (pulse) Imagine a sine wave. (maybe draw one on a piece of paper) Now draw a sine wave at 2x that frequency. Combine them. Now you have a wave the same frequency of the original sine wave, but not a sine wave, it starts to look more square. Do this again and again, and it becomes closer and closer to a square wave.

A square wave is a sine wave, with every even harmonic added to it. So it won't just interfere with a single frequency, but all over the spectrum. Power has nothing to do with it. PWM should not be used in proximity to the VHF antenna.

This is made worse by feeding that signal into a diode. A diode *IS* a transmitter. So now you are explicitly transmitting that wave and all the harmonics from the LED bulb itself.

[Lake-Effect]

Originally Posted by wholybee

A diode *IS* a transmitter. So now you are explicitly transmitting that wave and all the harmonics from the LED bulb itself.

A LED is a transmitter of photons . As a transmitter of RFI, that depends on a whole lot more: how much of the harmonics are present in the PWM drive, and with what efficiency the diode plus its wiring transmits that RFI. With proper layout and design, and especially with choking out the higher harmonics of the PWM, there should not be very much RFI at all at VHF ... it's just that some manufacturers have cheaped out.

[team karst]

LED’s themselves do radiate, but very little at VHF. The wires ahead of the PWM power supply make up the vast majority of vhf energy loss, in the form of radiation. A large led array, different story. Rule of thumb is one tenth wavelength or greater of pcb traces or wires have decent radiation capability. Marine vhf is around 6 foot wavelength.

[team karst]

Originally Posted by wholybee

The issue is that is is a square wave. (pulse) Imagine a sine wave. (maybe draw one on a piece of paper) Now draw a sine wave at 2x that frequency. Combine them. Now you have a wave the same frequency of the original sine wave, but not a sine wave, it starts to look more square. Do this again and again, and it becomes closer and closer to a square wave.



A square wave is a sine wave, with every even harmonic added to it. So it won't just interfere with a single frequency, but all over the spectrum. Power has nothing to do with it. PWM should not be used in proximity to the VHF antenna.



This is made worse by feeding that signal into a diode. A diode *IS* a transmitter. So now you are explicitly transmitting that wave and all the harmonics from the LED bulb itself.

Not reading much here that is correct. Freq content of sq waves are odd harmonics.
The actual device making trouble is the switching fet in the power supply. But, critically, that is not the device radiating. And definitely not the leds, either.
Whats happening is the wires are subjected to rapidly changing currents. In other contexts, they are called antennas.