Handleiding Icom IC-M802 (pagina 73 van 78) (Engels)

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2001 NEW

ANTENNA AND GROUNDING CONSIDERATIONS

terline ground system and attached directly to each piece of

low and high frequency radio gear.

While this may also seem to be an insurmountable problem 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 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 type, for that type tends

to cancel oscillating radio frequencies. Flat is best.

There are several sticky marine compounds that will allow

the foil to adhere to the underside of a hatch, or to the side of

a hull. Almost anything will work, and there is little danger of

any substantial amounts of voltage developing on your

ground foil run. The ground foil and your complete RF

ground system, which run inside the hull, also will not sub-

stantially change your corrosion exposure to the seawater.

Galvanic corrosion problems occur when dissimilar metals

are immersed in seawater. The ground system is not actu-

ally immersed, its coupling is only capacitive.

Electrolysis is another form of corrosion where stray currents

may begin to eat up underwater metals. Good wiring tech-

niques for your 12-volt system independent of your RF

ground system will eliminate electrolysis.

Now let’s get back to ﬁnding a spot to terminate that three-

inch wide copper foil that emanates from the below waterline

ground system. Most manufacturers of Loran weather fax

and marine single sideband sets don’t provide an easy way

of adding ground foil to the stern end of their electronics! The

best method is to run the foil up to the back of the equipment

and use existing sheet metal screws to make a ﬁrm connec-

tion. Where a ground post stud with nuts and a washer are

provided, all the better— run the foil up to the stud, double it

back on itself several times for strength, punch a hole in it,

and then make the connection. Never negate all your hard

work of running the foil by using a small jumper wire to inter-

connect the foil to the radio set-up. You will be putting a

“weak link” in your ground system at radio frequencies.

We usually accordion up the excess foil in back of the equip-

ment so that we might remove the equipment for servicing

with the foil attached. If you put the bends in the right spot,

the foil will resume its natural collapsed state when the

equipment is put back in place. Watch out for the sharp cor-

ners on the ground foil, they are capable of piercing through

the plastic protective covering on electrical wires. Make sure

that red and black voltage carrying wires are not allowed to

rub up against the side of the ground foil.

We usually ground everything with foil at the navigation sta-

tion. This would include the casing of the wind

and speed equipment, pilot control box, GPS, sideband,

radar, VHF, and just about everything else that lights up. The

more grounding you provide for your central electronics, the

less problems you will have with stray RF.

The ground foil must also run to remote tuners. This includes

the tuner on your Loran antenna set-up as well as the ICOM

single sideband tuner that’s usually several feet away from

the equipment. These tuners may be all the way back aft,

adding another dimension to your ground foil run. It’s best to

run the foil from the RF ground source directly to your tuner,

rather than stringing everything out in series like Christmas

tree lights. Now picture one ground foil run from the keel bolt

to the electronics, and a second ground foil run from the keel

bolt back aft to the sideband tuner and your stern-mounted

Loran whip. These tuner ground circuits are mandatory for

any type of reliable operation. If you try to run an ICOM side-

band set with a remote tuner that is undergrounded, you

stand the chance of not only burning up your equipment, but

also damaging other electronics onboard with stray RF. If it’s

not easy to run ground foil from your central below the wa-

terline ground source back aft, then try to ﬁgure out another

way to do it. It has to be done!

You can also pick up additional ground counterpoise surface

area by adding substantial metals along the way in your cop-

per foil run. Stainless steel hose clamps make it easy to pick

up through-hull bronze ﬁttings, water tanks, copper hydraulic

lines, and anything else that may give you some additional

underwater surface area.

Mariners with sailboats with poured incapsulated lead keels

as well as metal hull vessels have the easiest time in obtain-

ing a good ground counterpoise. If the keel is visible, a sec-

ond nut on the exposed thread will anchor on the ground foil.

We usually seal this connection to prevent deterioration from

the bilge water. It may also be recommended by local ex-

perts to tie in the aluminum mast to this close proximity keel

bolt for lightning protection. The run from the mast to the keel

bolt must be smooth, direct, and without sharp turns in order

to pass lightning energy effectively into the underwater lead.

Again, consult local lightning experts.

Steel-hulled vessels are easily attached to with foil by scrap-

ing away any protective coating from the hull, and making a

low resistant good surface area contact. Again, seal this con-

nection well. Non-metal hull or keel boats require yards and

yards of foil to be run below the waterline, anywhere you

can, and picking up any other large below the waterline tanks

and tubes.

SUMMARY

If you follow these steps, you will have an outstanding single

sideband signal that can be heard around the world. The dif-

ference between a good and bad ground is easily noticed on

transmission as well as reception. Since your ground coun-

terpoise is actually a part of your complete antenna system,

pay just as much attention to RF grounding as you did to

putting up that white ﬁber glass whip or installing to your in-

sulated backstay.

IC-M802_USA.qxd 02.7.9 10:59 Page 65

Icom IC-M802 Handleiding

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