LED Lamps and Radio Interference

Electrical and electronic topics for small boats
jimh
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LED Lamps and Radio Interference

Postby jimh » Sat Dec 02, 2017 11:40 am

Regarding LED lamps and operating a radio near them: there are two cases of interference:

--the LED lamps make radio-frequency noise that interferes with radio reception, and

--the transmission of radio-frequency signals from the radio interferes with the LED lamps.

The first case, LED lamps generating spurious radio-frequency (RF) noise, is perhaps the greatest concern. An LED lamp could generate enough spurious RF noise that reception of radio signals by your communication radio would be significantly affected; this could be a safety concern.

Typically one would not expect the flow of 12-Volt DC current through a diode-junction inside an LED lamp to produce much RF noise. You can operate LEDs directly from 12-Volts if you include a current limiting resistor in series. However, this is not a good method for conserving electrical energy, which is often the goal of using LED lamps in the first place. With a series resistor, most of the electrical energy in the circuit is consumed in heating the resistor and only a small portion goes to making light with the LED lamp. Accordingly, many LED lamps include an integral voltage convertor, shifting the 12-Volts down to much less voltage, just enough--a Volt or two--to power the LED.

Usually the noise is generated by these integral DC to DC voltage convertors. These devices use a switching voltage convertor, and to reduce size usually cannot have the necessary inductors or capacitors to filter out the noise. They become, in essence, little radio transmitters emitting a broad spectrum of radio-frequency noise.

As for the other case, the radio signal interfering with the LED lamp, this should not happen unless the LED lamp is very close to the antenna of the radio. It is a general goal of any antenna installation for transmitting to get the antenna away from all other devices and in the clear, so typically the antenna won't be close to any LED lamps. This also helps on receive--the antenna should be far away from any LED lamps and their RF noise. If an LED lamp is very close to a radio transmitting antenna, there may be current induced in the LED lamp from the RF energy. This current could cause damage to the circuitry of the voltage convertor or damage the LED lamp itself.

The exception to the physical separation of the antenna from LED lamps occurs when an LED lamp is used at the top of a mast and a radio antenna is also installed there. That co-location creates the possibility of interference in both cases, receive and transmit. I recall some anecdotal reports that use of an LED lamp for a navigation light atop a mast where the VHF Marine Band radio antenna was located, as often occurs on sailboats, resulted in interference to radio reception when the LED lamp was illuminated.