A single-sideband radio is one of the most important pieces of gear you can add to your bluewater voyaging boat. Aided by the introduction of commercial and private shore stations that allow the sending and receiving of email at sea, SSB radio has enjoyed a resurgence in popularity in recent years. The bad news is that installing an SSB radio is rarely an easy task, and the antenna ground system is usually the culprit.
The typical marine SSB installation consists of a radio transceiver connected to an automatic antenna coupler through coaxial cable. One output terminal of the coupler connects to the backstay, which is insulated from the mast and the chain plate. The other terminal connects to a ground system that consists of a series of copper straps or screens bonded together and secured as low down in the vessel as possible. Electrically coupled to the surrounding salt water through the hull, the result is a very efficient antenna that can communicate worldwide. However, this is all dependent on whether or not you can devise a good ground system in your hull. Owners of steel and aluminum boats have it easy, but if your boat is fiberglass or wood, you are not so lucky. Unless the builder installed a ground system before the interior went in, you will have to retrofit some compromise solution and hope it works well enough.
Those who don’t want to rip apart their floorboards and cabinets will be glad to hear that there are other types of antennas that do not require ground systems. Not all yachts will be able to use these types, but if your boat can, you will avoid the complications of trying to install an adequate ground system in an already built boat.
A good candidate for a no-ground marine antenna is the loop antenna. As the name suggests, it is a loop of wire. It can be almost any shape, the most efficient being one with the greatest internal area. This would mean a perfect circle. The circle shape is never used because the support structure required would be impractical. A realistic configuration for small boats is the triangle shape. This type of antenna is known as a delta loop because of its resemblance to the Greek letter. A loop antenna can be fed with a radio signal anywhere on its perimeter: at a corner or in the middle of a leg. Just break the wire where it’s most convenient and insert the antenna coupler. The coupler output goes to one end, and the output that would normally go to ground is connected to the other.
Due to the narrow shape of a boat, you have to accept a trade-off between the ideal shape and getting the most wire aloft. If you try for an equilateral triangle, the shape would be good, but the overall size would be quite small. On the other hand, a loop that is too narrow could make it hard for the coupler to match. Therefore, the wider you can make the base, the better it will perform. Some new voyaging boats are being designed with wide sterns that help in this area. Before undertaking any rigging modifications, you should construct a temporary version out of wire to make sure your coupler can handle it. Make it as close to the same size and shape as that planned for the permanent one.
and secure them with cable clamps or stainless-steel hose clamps as shown. If you are using cable clamps, be careful not to distort the rigging wire; remember it also holds your mast up. Spray the connections with a protective coating of paint to inhibit corrosion. Don’t forget to inspect these connections regularly.
It’s best to keep the bottom section up high, out of easy reach. If you have planned it right, the base wire will run right through the spot where your coupler is mounted. A radar mast or radar arch would come in handy here. Run a connection from the coupler terminals to each leg to complete the loop. Use 12- or 14-gauge marine-grade stranded wire for this connection. It is big enough to handle the antenna current efficiently and still allows for the use of a ring terminal connector that will fit on the coupler. Some kind of strain relief is necessary if these wires will put too much stress on your coupler’s terminals. Do your best to keep the entire loop flat, that is, all in the same plane. Some bending of the loop plane where the coupler attaches may be unavoidable, depending on the coupler mounting position; plan for the best configuration possible. Since the coupler must be located at the antenna, it will be outside in the weather. You should construct a non-conducting cover to protect it from rain, spray and direct sunlight, which can cause high temperatures inside the coupler box.
What do you do if you cannot mount the coupler in line with the bottom corners? Place the coupler in the lazarette to give it protection from the elements. Then run wires to the bottom corners to complete the loop. The main problem here is that these wires, which are within reach of the crew, will develop high voltages when the transmitter is operating. For safety, use wire with high-voltage (25-kilovolt) insulation. You will also require insulated fittings to bring the connections out to the antenna. Small-diameter PVC pipe or hose slipped over the accessible parts of each wire gives a little extra protection from shocks and makes them more visible.
The antenna is now more of a diamond shape, but this will help due to the increase in loop area that results. However, part of the antenna is near the stern railing and lifelines. The proximity of any metal will reduce the efficiency of the antenna and alter the radiation pattern somewhat, but few antenna locations are ideal. In the end, these two factors will probably cancel each other out.
Ketch and yawl rigs
A boat that is yawl- or ketch-rigged usually has twin backstays that lead to chain plates aft of the mizzenmast. These shrouds can have the lower insulators installed at a point that will allow the base leg to pass just in front of the mizzen. The coupler can be mounted on the front of the mizzenmast like a radar antenna. This gives a fairly wide base with good loop area and all active parts out of reach.
If you can’t use twin backstays, you may still be able to install a semi-permanent wire loop if the boat has a mounting location for the coupler that will keep the antenna away from the backstay. A radar arch or dinghy davits may work. This might be just the thing for crews that do delivery trips or a boat that makes only an occasional offshore passage. A wire-loop antenna hoisted on a spare or makeshift halyard could be put up temporarily and lowered when not in use. Having the backstay adjacent to your antenna is not exactly good radio practice, but you can’t avoid being close at the masthead. Even so, you should still be able to get satisfactory performance. Fortunately, it doesn’t cost much to experiment.
A simple way to build a temporary loop antenna is to run a single length of wire from one corner of the stern through a small block near the masthead and back to the opposite corner. Use only stranded wire, at least 14 gauge, preferably marine grade. By anchoring one leg with a small-diameter non-conducting line, you can tension both sides evenly by pulling on the other. You will need an adjusting device to keep everything tight. It should be non-conducting, a trucker’s hitch or a small block and tackle made from dinghy hardware.
There should be an insulator at the bottom of each leg and at the top, if you are using a wire halyard. Small plastic or ceramic insulators are available at hobby electronics outlets, or you can make your own by drilling two holes in a piece of strong plastic or other non-conducting material. Plastic kitchen cutting boards are easy to cut and cheap; you don’t have to steal the one in the galley. In an emergency, you can use a loop of rope or even the plastic tabs from a six-pack. Position the apex about five feet from the masthead and make the base as wide as you can. If you are really determined, you could incorporate outriggers to make the base even wider and give the loop more area. Use a non-conductive material, such as bamboo or wood, with shrouds to prevent flexing. Now connect the base leg the same way you would if you were using the backstays.
To maximize antenna performance, follow good electrical practices with the rest of your radio system. Mount the radio as close to the batteries as possible. Use large-diameter wire, only as long as necessary, for the DC connections to the radio. This will minimize the voltage drop along its length. Put fuses in both the positive and negative leads. Consider replacing your wire topping lift with a fiber-based line to minimize the amount of metal near the antenna.
The loop antenna as described here cannot outperform a properly installed backstay/ground-plane antenna, mainly due to the difference in electrical size and the fact that it is narrower than the ideal loop shape. But this is in theory only. Radio engineers characterize antenna performance under conditions they call “free space,” a situation that does not occur on Earth or any other planet for that matter. In practice, many installations suffer from poor grounding, corroded connections, weak batteries and various other ailments. For this reason, you may find the loop antenna works as well or better than the backstay antenna on another boat.
If you can, by all means install a good ground system in your hull and use the backstay for your antenna. If you are having a boat built, ask the builder to incorporate a ground system in the hull itself. If they are not sure what to do, get an experienced radio technician to give recommendations. This would give you the best antenna you can have on a sailboat. But, if you are planning an installation on a finished boat, the loop antenna may be an acceptable compromise.
Alan L. Smith is a sailor and amateur radio operator in Richmond, British Columbia. He sails his Brent Swain 30 sloop, Simplicity, along B.C.’s south coast and Vancouver Island.