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Safe at Sea: Radio check

By Staff | Sep 3, 2019

One of the last things you should do before throwing off the lines and slipping the engine into gear is to confirm the proper operation of your VHF transceiver for both receiving and transmitting.

The receiving part is no problem – tune to the weather channel.

The transmitting part is, for many, such a bother that it is left undone. Although it is often ignored, there is a FCC rule that prohibits you from broadcasting a radio check request. Such a request must be directed to a known station. In addition, the radio check cannot be carried out on Channel 16.

If you own a hand-held as well as a fixed-mount VHF transceiver, you can easily confirm the operation of both by tuning them to the same idle working channel, briefly keying them on in turn and listening for the clicks in the “listening” radio.

If you own a transceiver with Digital Selective Calling, testing it is very simple. Select “TEST” in the call menu and enter the following Mobile Marine Service Identity (MMSI): 003669999. Press send and a message will go from your radio to the nearest Coast Guard Rescue 21 antenna. (Locally, there’s one of these antennas on Pine Island, near the intersection of Stringfellow and Pine Island Roads. Its range is about 30 nm.) When the message is received correctly, after a few seconds a Coast Guard computer will send you an acknowledgment, which will be displayed and sounded on your transceiver.

For a somewhat more “personal” touch, there’s Sea Tow’s Automated Radio Check. It is utter simplicity – switch to Channel 27 (or 26, according to your location), push the talk button and say anything you want into the microphone. (The FCC prohibits using profane, indecent and obscene language, so not actually anything you want.) Release the button and immediately you’ll get an automated response from Sea Tow that includes a recording of whatever you said into the mic, as received by their base station. The response will include some other useful information as well, to remind you that this service is provided by a commercial concern, but you will have a good indication of how your transmitter is working without actually talking to anybody.

The Automated Radio Check response tells you that your transmission was received, but you might like to know just where it was received. Your radio technical officer was curious about this himself and did some research to give you an answer. Sea Tow has established Automated Radio Check base stations up and down the west coast of Florida, as well as most other coasts of the U.S. You can find the locations of these stations, wherever you are, by visiting seatow.com/tools-and-education/automated-radio-check and entering your location. Locally, the stations are at Burnt Store Marina, the western end of the Cape Coral Bridge, near Wiggins Pass at the intersection of Vanderbilt Drive and Wiggins Pass Road, and south of Naples near Gordons Pass. These operate on Channels 26 or 27.

The distance over which you can communicate using Marine VHF is limited by the “radio-line-of-sight.” This basically means that if you can see one antenna from the other antenna, you will be able to communicate. Although some complexity is introduced by the atmospheric of the VHF waves, the ultimate obstruction between transmitter and receiver is the curvature of the Earth itself. There is a formula that considers both the refraction and geometry factors to predict the communication range. It depends only on the heights of the two communicating antennas above the water. Your radio technical officer set out, with sextant, laser ranger and calculator in hand, to find the heights of the two local antennas used for this service, with the intent of estimating their range.

The results of this exercise are shown in the accompanying chart. The range plotted assumes that the height of your boat’s antenna is 10 feet over the water. If it different from that, adjust the range given using this formula: Additional range in nautical miles = 1.32 times (the square root of the antenna height in feet), minus 4.2 nautical miles.

The line-of-sight formula cannot account for obstructions above the water level, so it is somewhat optimistic when there is something besides water between the communicators. Based on that, one might not expect the Cape Coral station to be able to receive signals from the Gulf side of Sanibel and Captiva, although the plot predicts it. It may be OK in Pine Island Sound, however.

The station at the Cape Coral bridge operates on Channel 27. The station to the north (Burnt Store Marina) and both of the next stations to the south (Wiggins Pass and Gordons Pass) operate on Channel 26. There may be some places where both of the Channel 26 stations receive you, but apparently, there is a feature that prevents both from responding

The generous assistance in the preparation of this column provided by Capt. Dan Mercier, Sea Tow franchise owner for Southwest Florida, is gratefully acknowledged.

Ron Wallace is a member of America’s Boating Club of Sanibel-Captiva. For more about the chapter and the courses it offers, visit www.sancapboating.club or contact education@sanibelcaptivasps.org or 239-985-9472.