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Q: Is it common that transmitting on marine single sideband will cause an automatic pilot to abruptly change course?  This could be dangerous for those on deck when the boom suddenly swings. 

Vincent Andrews, Aberdeen, MD

GORDON WEST REPLIES

All too common! Your long-range single sideband radio emits radio frequency interference that couples to the wiring associated with a fluxgate compass. This, in turn, creates a heading sensor error, sometimes leading to an accidental gybe or an abrupt change in course—all dangerous. Don’t blame the radio or the installation; it is the proximity of the backstay or the long whip antenna off the stern that causes the coupling to your automatic pilot wiring. There are no filters to go on the radio to cure this job, and it would take hours of trial and error ferrite chokes on various parts of your autopilot wiring. The NMEA 2000 can bus wiring may be less prone to SSB radio transmissions. Short of encapsulating your entire autopilot brains in a Farraday screen tent, the only real solution is telling the helmsman to steer by hand as you are giving your morning race position report.

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January 2017

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