— May 2003
By Ben Ellison
Someone at the marina
told me that there's a warning out about TV antennas messing up
GPS. Please explain. B.T., via e-mail
Fairly few antenna units were manufactured with the faulty piece (Shakespeare estimates that only 400 left its factory), but if you have an active TV antenna, you should definitely check it out. For starters, turn on your GPS at the dock with the TV antenna turned off, then turn on the antenna, tune to a TV station, and see if your position changes or gets lost. You might also go to the U. S. Coast Guard safety site (www.uscgboating.org) to get a list of affected models. If you have one, you'll find that the manufacturer has a program to further identify and replace defective units.
Overall, this is not a huge problem, but there is an aspect to it that all navigators should consider. The authorities have documented cases when the faulty antenna didn't just jam the GPS signal but actually caused false positions and even affected GPSs on other boats within 2,000 feet of the bad transistor. This confirms the fears of many, including some observations I made in my April 2002 column called "The Dark Side of GPS." As marvelous and 99.9 percent reliable as GPS is, it is always a good idea to use independent means--radar, Loran, soundings, visual bearings, etc.--to double-check your position.
Got a marine electronics question? Write to Electronics Q&A, Power & Motoryacht, 260 Madison Ave., 8th Fl., New York, NY 10016. Fax: (917) 256-2282. e-mail: PMYElectronics@primediamags.com. No phone calls please.
This article originally appeared in the April 2003 issue of Power & Motoryacht magazine.