Icom M802 Instruction Manual - Page 71

14 ANTENNA AND GROUNDING CONSIDERATIONS ANTENNAS & TUNERS If your Icom SSB is going aboard a sailboat, you may either use an insulated backstay an insulated sidestay, or a nonresonant white fiber glass whip antenna off the stern to make up your antenna system. Your best range will be from an insulated backstay because of the long length of the antenna "radiator" which is that portion within the top and bottom insulators. Have your rigger put the top insulator about at least 3 feet down from the tip of the mast. Have your rigger install the bottom insulator at about eye-level when you're standing back aft. (This length between insulators should not exceed 120′ or be less than 23′.) If you decide to go for the non-resonant whip antenna, the antenna usually goes at the extreme stern and mounts either vertically or raked back at about a 45-degree angle. These non-resonant antennas may be tuned by the ICOM automatic antenna tuner that matches the Icom SSB transceiver. The tuner goes back aft, in the lazarette, or as close to the antenna as possible. It is completely weather-protected and can easily take the punishment of being aft and below deck where you're probably also going to store wet life preservers, foul weather gear and the like. The tuner interconnects with the Icom SSB. Full details are in the tuner instruction (installation) manual. We suggest you use "GTO-15" high voltage lead-in wire from the single wire output of the tuner to your insulated backstay or to your nonresonant whip. This high voltage wire won't break down in wet weather or sunlight. Use stainless steel hose clamps to attach the wire to the insulated backstay. If you decide to use a non-resonant whip, attach the single wire with a lug to the feedpoint at the base of the whip. More about the importance of grounding in a moment. For those of you with a powerboat, a whip antenna approximately 16 to 20 feet long is what you'll be using with your new Icom SSB. The most common set-up consists of the white fiber glass non-resonant whip antenna that is automatically tuned with the ICOM automatic antenna tuner. Similar to sailboat installations, the tuner is hidden out of the way in the flying bridge area or below deck near the base of the whip. GTO-15 wire interconnects the whip to the automatic tuner. The tuner is fed with coax (RG 213) and a control line from the back of the Icom SSB wherever you plan to hide the auto-tuner. Remember, the ICOM automatic tuner is fully automatic, so you can put it completely out of sight! We suggest you check with the dealer that sold you your transceiver to purchase the ICOM automatic tuner as well as a resonant or non-resonant whip antenna assembly. Dealers that sell ICOM equipment usually have these accessories on hand. THE IMPORTANCE OF GROUNDING Please read this! If you are looking for "super range" with your new Icom SSB, we have some tricks that will give you the same kind of range as globe-circling cruise ships, super tankers, solo sailors, the Navy and the Coast Guard. Surface area to the sea water and the use of copper foil exclusively throughout your RF ground system is the combination that gives you commercial-type "super range." The sea water acts like a diving board or side of a pool for a diver and a swimmer- it gives your signal a solid surface to push off from. This is technically called a "counterpoise", and it's the absolute necessary "other-half" of your antenna system that must be achieved for your overall single sideband system to work well. It's not that hard to develop your own sideband RF ground system in just about a day's time, and you may even find that most of the RF ground system is already installed so you have little to do but to tie everything together with copper foil. Read on, please, and let us show you how easy it can be. NON-TECHNICALLY SPEAKING If you plan to have a technician or a technical friend install your sideband system, have him skip this part and begin reading at "Antenna Ground Principles, Technically Speaking." If you plan to do the installation yourself, and this is the first one you've done, read on! The water that your boat sits in is the ultimate ground counterpoise. There's none better. Commercial AM broadcast stations on the coast usually put their giant antenna system in the mud flats of a local bay for good range. Some boat suppliers put ground foil and ground screen in the cabin overhead. This is true on expensive powerboats, and is sometimes found in a few sailboats. While this type of overhead RF ground system is better than nothing, it still lacks the capability of coupling with the ocean or lake as the ultimate water ground system. A far better RF ground system would be the following: • 100 sq. ft. area of foil below water line • Metal water tanks • Lead keel • Foil radials • Interconnected through-hull The whole idea is surface area- and this is why a keel bolt, underwater tanks, through-hulls, and anything else flat and next to the water does such a good job. Now we know your next question, "But doesn't a good ground actually have to be in contact with the water?" Not at all! At radio frequencies (RF), your underwater ground counterpoise sees the water in a capacitive way, which gives just as good a ground effect as if it were actually touching the water! Now here's another very important point, no round wires for RF ground! Even if you use welding wire the size of your thumb, you cannot achieve a good ground counterpoise with round wire. In our "Technically Speaking" section, we'll tell you why, but, in non-technical terms, round wires tend to cancel out at radio frequencies, and they look invisible as a ground counterpoise interconnect. This is why copper foil must be used between the chassis of your transceiver to your ship's RF ground, as the chassis of the automatic antenna tuner to ship's RF ground. Your better marine electronic stores that sell ICOM equipment will also sell three-inch wide, super-thin, copper foil for grounding. In a pinch, you can use one-inch wide copper plumber's tape. Three-inch is better. Note: A three inch strip mounted three inches away from another three inch strip of copper foil looks like a nine inch strip to a radio wave. It's going to take you about a day to work this foil below decks and below the water line picking up anything and 13 14 63