LED lights interfering with VHF/DSC/AIS

How do you find them? Is it just a matter of switching things off until it goes away or improves?

That’s usually how you find them. I was on a seismic vessel years ago with a bad hash problem. I borrowed a small short wave receiver from an AB. Turned the RF gain down and strolled about the vessel until the noise peaked. Turned out to be a bad capacitor on the A/C condenser fan motor.

3 Likes

That’s a smart way to do it. I wonder if there’s a tool that’s meant for this. I’ve never heard of using radio to diagnose machinery problems. Maybe fluke should… oh hey. Would this do the trick?

In the case of the problem with the LED lights this is what the CG says.

Strong radio interference from LED sources may not be immediately evident to maritime radio users. Nonetheless, it may be possible to test for the presence of LED interference by using the following procedures:

  1. Turn off LED light(s).
  2. Tune the VHF radio to a quiet channel (e.g. Ch. 13).
  3. Adjust the VHF radio’s squelch control until the radio outputs audio noise.
  4. Readjust the VHF radio’s squelch control until the audio noise is quiet, only slightly above the noise threshold.
  5. Turn on the LED light(s).
    • If the radio now outputs audio noise, then the LED lights have raised the noise floor. (Noise floor is generally the amount of interfering signals / static received beyond the specific signal or channel being monitored.)
  6. If the radio does not output audio noise, then the LED lights have not raised the noise floor.
  7. If the noise floor is found to have been raised, then it is likely that both shipboard VHF marine radio and AIS reception are being degraded by LED lighting.
2 Likes

No, that’s for in-circuit use. Minimum specified signal is 250,000 microvolts.

Any decent receiver in the band of interest, preferably with an RF or IF gain control and switchable AVC, is exactly what you want. If it has an S meter that could possibly be helpful along with a directional antenna; but not as much as you might think for near-field work.

As of today, I’ve changed out all fluorescent and incandescent lights in my home and camp house with LEDs. I checked radio frequencies from 500 khz to 430 mhz all modes with no interference.

My camp house is in a salt prairie very close to the surf. The power lines in the area can create noise from time to time from salt dust build-up on insulators, cracked insulators or loose taps. We have methods to pinpoint the faults with an AM 450 mhz receiver with a 5 element yagi antenna and an ultrasonic receiver with a 18 inch parabolic dish.

2 Likes

Never seen the term “noise floor” before.

In signal theory, the noise floor is the measure of the signal created from the sum of all the noise sources and unwanted signals within a measurement system, where noise is defined as any signal other than the one being monitored.

In radio communication and electronics, this may include thermal noise, black body, cosmic noise as well as atmospheric noise from distant thunderstorms and similar and any other unwanted man-made signals, sometimes referred to as incidental noise. If the dominant noise is generated within the measuring equipment (for example by a receiver with a poor noise figure) then this is an example of an instrumentation noise floor, as opposed to a physical noise floor. These terms are not always clearly defined, and are sometimes confused.[1]

Avoiding interference between electrical systems is the distinct subject of electromagnetic compatibility (EMC).

In a measurement system such as a seismograph, the physical noise floor may be set by the incidental noise, and may include nearby foot traffic or a nearby road. The noise floor limits the smallest measurement that can be taken with certainty since any measured amplitude can on average be no less than the noise floor.

A common way to lower the noise floor in electronics systems is to cool the system to reduce thermal noise, when this is the major noise source. In special circumstances, the noise floor can also be artificially lowered with digital signal processing techniques.

Signals that are below the noise floor can be detected by using different techniques of spread spectrum communications, where signal of a particular information bandwidth is deliberately spread in the frequency domain resulting in a signal with a wider occupied bandwidth.

I was thinking about tide and current thread, in some locations the “signal” from the changing gravitational field is above the “noise floor” but in other places, further up river the river current hides the tide below the noise floor.

Also in ocean basins that are properly tuned, for example the Bay of Fundy the tidal signal is amplified*, like an antenna.

EDIT: *Antenna gain is a more accurate term I see as the antenna does not add energy to the signal, that would be a amplifier.

1 Like

Various type of antennas can focus the energy. The gain is measured in decibels. (DB) For every 3 DB gain, you double the effective radiated power. You also increase the strength of the received signal.

Yes, the last sentence of my post was intended to correct the previous one, I see the term amplify requires energy to be added to be technically correct. The big tides in the Bay of Fundy is a result that is analogous to antenna tuning, not amplification.

1 Like

I have had a few eBay specials LED lights that were really good radio jamming devices for the SSB and a few of them did in the VHF too. Part of what you pay for with the “good ones” is RFI suppression.

1 Like

Any radio amateur or shortwave listener is intimately acquainted with noise floors, whether or not they know the term.

1 Like

Hi…i am a new user here. As per my knowledge Vf runs between 1.8V and about 4.5V for different types and colors. They need some sort of current limiting, a series resistor for small ones. Many power LED drivers also are buck-boost devices that will supply constant output over a considerable range of input voltage.

pcb assembly process

And it’s the driver electronics, not the actual LED, that creates the interference issue.

1 Like

This. Some power supplies noise performance with be worse than others. Some of the noise can be mitigated with proper shielding of the power supplies, chokes, shielded cable, etc.

LEDs can be powered by DC, in which case they will emit no RF noise, but then you cannot dim them. So as long as you don’t need to dim them you can have LED, and completely eliminate the RF noise.

Resistor regulated LED lights are noise-free, but have some drawbacks. Power is wasted in the resistor and the light output varies with the input voltage. Too much voltage will damage them and too little is very dim. When you see an LED light advertised to run on say 12 to 24 volts or 12-32, 12-36, or other wide ranges it has a regulator circuit in there somewhere that can possibly make a lot of noise. If you dig into it really deep, there are driver circuits that pulse the LEDs to get max light out of them without burning them out.
If I can get myself motivated to haul my test equipment out of the house, I’ll show you all a waterfall plot of one of these bad LED lights.

1 Like

Yeah I didn’t address that but you can certainly use a rheostat, and to be fair, the power usage wouldn’t be a big deal unless you were working off of batteries.

What I haven’t seen mentioned yet is LED flashlights, particularly ones with more than one brightness setting. Maybe we need a new version of the infamous Navy short-arm inspection.**

**They quit doing those not long before I became a Navy Corpsman. As a lab tech I was also spared having to keep a bunch of male frogs in my refrigerator, inject them with questionably pregnant urine, and check their urine later under microscope to see whether they had ejaculated – a slide test had become available which only required stirring a drop of mixed stuff on a black glass slide for a ridiculously long time and looking to see whether it agglutinated or stayed smooth.