Handleiding Icom IC-M802 (pagina 71 van 78) (Engels)

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ANTENNA AND GROUNDING CONSIDERATIONS

2001 NEW

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 in-

sulated backstay because of the long length of the antenna

“radiator” which is that portion within the top and bottom in-

sulators. 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-res-

onant 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 trans-

ceiver. The tuner goes back aft, in the lazarette, or as close

to the antenna as possible. It is completely weather-pro-

tected 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 inter-

connects with the Icom SSB. Full details are in the tuner in-

struction (installation) manual. We suggest you use

“GTO-15” high voltage lead-in wire from the single wire out-

put of the tuner to your insulated backstay or to your non-

resonant 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 approxi-

mately 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 auto-

matically tuned with the ICOM automatic antenna tuner. Sim-

ilar 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 au-

tomatic, 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 Speak-

ing.” 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 coun-

terpoise. There’s none better. Commercial AM broadcast sta-

tions 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 sys-

tem 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 an-

tenna tuner to ship’s RF ground.

Your better marine electronic stores that sell ICOM equip-

ment 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

IC-M802_USA.qxd 02.7.9 10:59 Page 63

Icom IC-M802 Handleiding

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