LED lights could be causing interference with AIS and certain VHF frequencies, according to the Coast Guard, which warns some users might not recognize the problem.
The agency has received numerous reports about poor reception for VHF frequencies used for AIS, radiotelephone and digital selective calling.
“Radio frequency interference caused by these LED lamps were found to create potential safety hazards. For example, the maritime rescue coordination center in one port was unable to contact a ship involved in a traffic separation scheme incident by VHF radio,” the Coast Guard said. “That ship also experienced very poor AIS reception.
“Other ships in different ports have experienced degradation of the VHF receivers, including AIS, caused by their LED navigation lights,” the alert continued. “LED lighting installed near VHF antennas has also shown to compound the reception.”
The Coast Guard described a five-step test to determine whether LED interference is affecting communications equipment. Start by turning off the LED lights and adjusting the VHF radio to channel 13 or another quiet channel.
Next, adjust the radio’s squelch control until the radio makes an audio noise, and then readjust the squelch control such that the audio noise is low, just slightly above the noise threshold. Then, turn on the LED lights.
“If the audio noise level increases, then the LED lights have raised the noise floor. (The noise floor is generally the amount of interfering signals/static received beyond the specific signal or channel being monitored.)
“If the radio does not output increased audio noise, then the LED lights have not raised the noise floor.”
In cases where the noise floor has been raised, the Coast Guard said it’s likely LED lighting has caused the degradation.
Mariners experiencing this problem can report it to the agency’s Nav Center www.navcen.uscg.gov.