Radio Frequency Interference RFi takes many forms and is a term generally used to cover the impact of uncontrolled Radio frequency emissions from one piece of equipment adversely affecting the performance of another piece of equipment.
The increasing use of LED lighting onboard vessels has coincided with an increase in interference affecting the performance of onboard VHFs, AIS, GMDSS and GPS systems. There are various published articles referring to one of the causes of the interference being attributed to the LED lighting systems themselves, whether the power supply, the transformers or even the lighting drivers themselves.
Examples range from situations where a maritime rescue coordination center in one port was unable to contact a ship that was involved in a traffic separation scheme incident by VHF radio. The ship involved was experiencing very poor AIS reception. AIS is dependent of using the VHF frequencies on the VHF radios for their communication links and are often integrated into the VHF transceivers. Other ships have experienced degradation of the VHF receivers, including AIS, caused by their LED navigation lights. The problem can be particularly severe when the LED lighting is installed near to the VHF antenna which has been shown to compound the reception problems which could account for the focus on navigation light sources of LEDs.
In a second example a customer installed two new LED spreader lights and both his VHF radios cut out when the lights are turned on. The power bar screen looked like he was transmitting on one of the radios and the other one just appeared dead even with local weather on. He never had any problems the previous year using halogen lights with the same wiring set-up.
A Final example was another customer just installed an LED tri-colour and an LED anchor light simply by changing a lightbulb. However, whenever the light is turned on (either one) he can only hear static on all stations on his VHF, no matter where the squelch is set.
LEDs don’t produce RF noise, however the LED drivers do. Although LEDs are efficient, the brighter ones do create heat which must be dissipated. As with any diode, a constant forward voltage applied sufficient to heat the device will cause current to increase, and if not limited will cause thermal runaway, causing it to fail. To avoid this problem, electronic LED drivers are necessary to regulate the current and maintain specified luminosity as input voltages vary and the LED heats up.
Low power LEDs that dim when voltage is reduced do not have regulators and will not cause RF interference. When regulators are used, LED drivers are normally part of the LED package itself.
The most efficient LED drivers operate with high switching frequencies which are necessary to reduce heat generated by the drivers as well as to minimize current consumption. The downside to this energy efficient LED driver switching circuitry is the generation of radio interference at higher frequencies. Switching circuitry has long been a source of HF interference.
Isolating the cause
It may be possible to test for the presence of LED interference by using the following procedures:
- Turn off all equipment onboard to create a full ‘quiet ship’ condition, this includes electronic navigation equipment, onboard domestic equipment, heaters, refrigeration, lighting systems, power generation equipment, pumps, fans and any other electric motors as well as engines. Disconnect any external power sources to effectively shut the vessel down.
- Turn the vhf radoio on, if possible only use a hand held vhf to eliminate any possible power supply induced interference
- Tune the vhf to a ‘quiet’ channel for example channel 13
- Adjust the VHF radio’s squelch control until the radio just outputs audio noise.
- Re-adjust the VHF radio’s squelch control until the audio noise is quiet, only slightly above the noise threshold.
- Turn on the LED light(s).
- If the radio now outputs audio noise, then the LED lights are causing interference and depending on the level of this interference it could prove difficult to receive valid signals on that channel. If the radio does not output audio noise, then the LED lights are not causing a problem.
If the interference noise 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.
Currently there is no EMC standard widely recognized by manufacturers of shipboard LED navigation and deck lighting.
Until a standard for shipboard LED lighting installed within three meters of VHF antennas is recognized, the best solution may simply be to ensure that any LED light purchased is warranted and then to perform EMC tests once installation is completed.
In short, those who may be considering use of LED vs incandescent lighting onboard their boats or have boats which have been manufactured with LED or CCFL lighting, please note that LED and CCFL lighting may interfere with receivers within marine electronics (ex. GPS receiver circuitry), communications equipment (VHF radio receivers, AIS receivers), and AM/FM receivers within entertainment systems. If experiencing such issues, the customer should test their systems under quiet ship conditions (to now include switching off all LED and CCFL lighting. Should the problem persist, then the customer may need to revert to incandescent lighting onboard the vessel.