Icom_-_Grounding_and_antenna_considerations.pdf

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1、INSTRUCTION MANUAL grounding and antenna considerations Icom Inc. FORWARD Congratulations on your purchase of an ICOM marine single sideband transceiver. You have chosen one of the finest sideband sets available. This special insert in your marine single sideband instruction and installation manual

2、will assist you in choosing the right antenna and getting the best range out of a good grounded single sideband installation. Good antennas and good grounding are absolutely essential for good single sideband range, and this is why this special report is included with your single sideband transceive

3、r. ANTENNAS & TUNERS If your ICOM SSB is going aboard a sailboat, you may either use an insulated backstay an insulated sidestay, or a non-resonant 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 leng

4、th of the antenna “radiator” which is that portion within the top and bottom insulators. Have your rigger put the top insulator about two feet down from the tip of the mast. Have your rigger install the bottom insulator at about eye- level when youre standing back aft. (This length between insulator

5、s should not exceed 120 or be less than 23.) If you decide to go for the non-resonant whip antenna, such as a Shakespeare or Morad, 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 ICO

6、M automatic antenna tuner that matches the ICOM SSB transceiver. The tuner goes back aft, in the lazarett. It is completely weather-protected and can easily take the punishment of being aft and below deck where youre probably also going to store wet life preservers, foul weather gear and the like. T

7、he tuner interconnects with the ICOM SSB. Full details are in the tuner instruction/installa- tion 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 non-resonant whip. This high voltage wire wont break down in

8、 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 p

9、owerboat, a whip antenna approximately 20 feet long is what youll be using with your new ICOM SSB. The most common and preferred set- up consists of the white fiber glass 21-foot, non-resonant whip antenna that is automatically tuned with the ICOM automatic antenna tuner. Similar to sailboat install

10、ations, 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. Reme

11、mber, the ICOM automatic tuner is fully automatic, so you can put it completely out of sight! Another antenna system for powerboat operation is the pre-tuned trap, 23-foot, aluminum whip from Morad, Inc. This antenna requires no automatic tunersimply feed it with coax out of the back of your SSB, an

12、d it works nicely on all of the pre-set marine frequencies. This antenna system must usually be tuned up by a technician, and it usually is not as popular as the non-resonant, white fiber glass whip used in conjunction with the ICOM tuner. Although both are good performers, the ICOM tuner and the wh

13、ite fiber glass non-resonant whip is usually the easier way to go. We suggest you check with the dealer that sold you your transceiver if you would like to purchase the ICOM auto- matic tuner as well as a resonant or non-resonant whip antenna assembly. Dealers that sell ICOM equipment usually have t

14、hese 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 t

15、o the sea water and the use of copper foil exclusively throughout your RF ground system is the com- bination 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

16、 technically called a “counter- poise”, and its the absolute necessary “other-half” of your antenna system that must be achieved for your overall sin- gle sideband system to work well. Its not that hard to develop your own sideband RF ground system in just about a days time, and you may even find th

17、at 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 h

18、im 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 youve done, read on! - 1 - The water that your boat sits in is the ultimate ground counterpoise. Theres none better. Commercial AM broad- c

19、ast 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 R

20、F 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: 1. 100 sq. ft. area of foil below water line 2. Metal water tanks 3. Lead keel 4. Foil radials 5. Interc

21、onnected through-hull 6. Engine block 7. Metal oil-catch pans 8. Steering system hydraulics Thats right, we list the engine block as last as a good underwater counterpoise. Engine blocks do not have an extremely large amount of surface area that is flat and close to the water your boat is sitting in

22、. The whole idea is surface areaand 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 doesnt a good ground actually have to be in contact with the water?” Not at all! At radio frequencies

23、(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 heres another very important point, no round wires for RF ground! Even if you use welding wire the size of your thumb, you cannot achi

24、eve a good ground counter- poise with round wire. In our “Technically Speaking” section, well 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 th

25、e chassis of your transceiver to your ships RF ground, as the chas- sis of the automatic antenna tuner to ships RF ground. Round wires wont work-only copper foil will! Your better marine electronic stores that sell ICOM equip- ment will also sell three-inch wide, super-thin, copper foil for groundin

26、g. In a pinch, you can use one-inch wide copper plumbers 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. Its going to take you about a day to work this foil below decks and below

27、 the water line picking up anything and everything of ground potential. If you can get at your keel bolt, or tap a screw into the keel, your grounding is done. Lead incapsulated keels are the ultimate in grounds, and you may need nothing further. In powerboats, since theres no keel, youre going to n

28、eed to come up with at least 100 square feet of RF ground surface below the water line. This means you must pick up as many ground potentials below the water line as possi- ble. We usually use a stainless steel hose clamp to grab each underwater metal source. Now lets take a look at grounding from a

29、 slightly more technical point of view. Dont worry, we wont get over- technical, and its easy to read and understand. If youre letting a technical friend of technician put in your equip- ment, make sure they read over this section several times. The facts here are based on hundreds of hours of doing

30、 and undoing, different types of ground systems. In all cases, following these techniques will give you the results that you want and thats long range and the loudest signal on the band. ANTENNA GROUND PRINCIPLES, TECHNICALLY SPEAKING The marine antenna system for low, medium, and high frequency app

31、lications will utilize both the seawater as well as that shiny white fiber glass antenna radiator for its entire operation. Like two kids on a teeter-totter, the sys- tem works well if there is a balance between the antenna radiator and the seawater ground. This balanced antenna system may electrica

32、lly be compared to a dipole antenna systemone-half wavelength long on the frequency band of operation with voltage and current loops equally distributed throughout the half-wave length system. In marine applications where a vertical antenna is used, this system is more precisely referred to as a Her

33、tz antenna set-up. The white fiber glass whip is tuned to an electrical one-quarter wavelength and the ground system will make up the other one-quarter wavelength. We technically call the RF ground system a “counterpoise,” and the antenna the “radiator.” - 2 - If either a one-quarter wavelength ante

34、nna or ground system is missing or inadequate, radio reception and transmission range will be severely reduced. How good was your car radio reception when someone broke off your whip antenna? The same degradation of range also takes place when there is little or no RF ground system for the whip to w

35、ork against in a marine installation. Imagine a swimmer making a flip turn, but not having the side of the pool to push off from. The same thing happens with radio wave transmissions on single sideband. The most powerful antenna will not radiate a signal if it has not counterpoise to push off the si

36、gnal from. In technical terms, the less RF ground, the higher the radiation resistance of the antenna system. This radiation resistance will lead to substantial power loss and single sideband equipment will not only perform poorly, but also get quite hot in the transmitter section. An inadequate sin

37、gle sideband RF ground will also lead to “hot mikes” where the operator actually receives a radio frequency burn each time the mike is held next to his mouth. Poor RF grounding will also lead to erratic movement of analogue dial instruments, bizarre behavior of automatic pilots while transmitting on

38、 the sideband set, and may even cause burn-outs of tiny integrated circuits in companion marine electronic gear aboard. Isolating your RF ground- ing system from your DC grounding system will prevent these unwanted occurrences. SURFACE AREA For marine SSB radios a good radio frequency ground sys- te

39、m will consist of a minimum of 100 square feet of metal below the waterline. Now we know youre going to jump out of your chairs when you read this, but dont be over- whelmed. There are plenty of underwater metals that we might attach to in order to obtain this amount of counter- poise below the wate

40、rline. Lead keels incapsulated within fiber glass will make excellent surface area grounds in sail- boat applications. The tough part will be getting to the lead keel or the exposed keel bolt. In other marine installations, stainless steel tanks, copper hydraulic lines, and through-hulls, will help

41、make up the RF ground counterpoise system. Boat manufacturers have the capabilities of adding a terrific RF ground system when the hull is being laid up. Lightweight copper screen is one of the best ways to provide a good surface area ground. Copper screen could be laminated inside the fiber glass l

42、ayers as the hull is under construction. Thin sheets of copper foil could also be used in the manufacturing process of the hull. Even the conducting mesh that holds together cement hulls can be used quite nicely as a ground counterpoise system. Copper foil and grounding screen is available from most

43、 marine electronic distributors as well as marine electronic dealers. Thickness of the screen and foil is not important, the most common foil is generally one to four mills thick and comes in three-inch wide rolls of just about any length you want. Copper window screen (if you can find it) is usable

44、, thickness is not important. Radio frequency energy travels on the outside of this conducting surface called skin effect, eliminating the need for thick grounding materials. Since grounding foil and screen is relatively expensive, most boat builders will simply leave out this grounding process and

45、expect the customer to provide their own RF ground once the boat is finished. This is a shameits so easy to build in when the hull is under construction, and far more difficult to add after the vessel is fully completed. The copper foil and screen does not actually need to con- tact seawater in orde

46、r to create the ground system. Radio frequency energy passes quite nicely through fiber glass, so an incapsulated ground system works just as well as one that is actually exposed to the seawater. Incapsulated lead keels with a half-inch of resin also work well. Any RF ground system that is capacitiv

47、ely coupled to the seawater is enhanced by the seawater itself. Developing the ground system for radio frequency appli- cations (as opposed to DC circuits) requires that all ground connections be interlaced using copper foil. Round ground wires are out! Wires actually look like inductive trapcir- cu

48、its at certain radio frequencies, and will appear invisible as an effective way of coupling your set to your ground system. Thats right, copper foil must be run from below the waterline ground system and attached directly to each piece of low and high frequency radio gear. While this may also seem t

49、o be an insurmountable prob- lem in running foil, rather than wire, foil handles quite nicely, even in tight places. The foil is easily soldered to the below waterline ground system, and then routed up the side of the hull into the area of the NAV station. It may be glassed into the hull, painted over, glued in, or even left resting on the side of the hull. The foil may be bent in order - 3 - to accomplish a 90-degree turn. If the foil must absolutely pass through a small hole, it may be rolled up in a not-so- tight configuration and squeezed through the orifice. Avoid a concentric