Interference with maritime radio reception by on board equipment

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The Club would like to make Members aware of several cases where interference from on board lighting has blocked reception of weaker radio signals, particularly deck / navigation lighting installations using compact fluorescent (affecting lower frequencies such as NAVTEX, MF and possibly HF) or LED lamps (affecting higher frequencies such as VHF including AIS). As yet, no effect on satellite communications has been noted from such installations.

Aside from on board lighting, the Maritime & Coastguard Agency’s (MCA) Safety Bulletin No. 8 highlights that there may be other sources of interference on board. Electrical/electronic equipment and associated cables may interfere with radio reception. In addition, installations of products designed for domestic use are not always compatible with marine radio reception. Even installations of type-approved equipment may cause a problem if positioned too close to a receiving aerial or improperly installed.

An affected vessel is able to transmit radio messages but may fail to receive follow-up communications. It is essential that a vessel can properly receive GMDSS communications including emergency and safety broadcasts, working channels and AIS signals, if any.

The symptoms of interference are not the same for all GMDSS equipment and particular attention should be paid to the radio telephone (i.e. sudden loss of reception or audible interference), DSC reception (i.e. failure to receive DSC messages), NAVTEX (i.e. garbling or loss of text), and AIS (i.e. loss of distant targets) as symptoms of interference.

Members should be aware of this safety issue and regularly check for the signs of interference as detailed above. Any anomalies that are found should be brought to attention of the vessel’s Flag/Class. Relevant entries should also be made in the log books, especially the GMDSS log book, and assistance should be sought from shore based radio technicians, as required. Radio transmissions made especially to check or isolate this issue should be at low power, should not interfere with normal operation of distress or safety channels and should not involve Coastguard stations. This full notice can be found here.

In August 2018, The United States Coast Guard (USCG) also released a safety alert warning of the potential for LED lighting to compromise reception on VHF frequencies used for radiotelephone, Digital Selective Calling (DSC) and Automatic Identification System (AIS). They recommend pro-actively testing equipment to see if interference is being experienced with the below steps;

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. Re-adjust 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.