Advanced Marine Electrics and Electronics Troubleshooting A Manual for Boatowners and Marine Technicians

including ICOM, specify a minimum

width of 3 inches.)

Because copper foil is the most common

method for creating a counterpoise, we’ll dis-

cuss that method in more detail.

Creating a Counterpoise with

Copper Foil Tape

First let’s go over a bit of background. We use

foil instead of insulated copper conductors

because radio frequencies do not travel through

conductors—they travel on the surfaceof con-

ductors. This phenomenon is sometimes

referred to as the skin effect, and the greater the

surface area, the better. One hundred square

feet is often recommended as the minimum

surface area for an effective ground plane. That

number may seem high, but you can achieve it

rather easily by tying in various bits of metal on

the boat with the copper foil tape. Good

choices include metal through-hull fittings,

metal water tanks, and encapsulated lead keels.

The best pieces of metal are those that are

located below the waterline because they will

achieve an effective capacitive counterpoise to

the seawater; that is, without necessarily having

a direct connection to the seawater.

Warning: Never use a metal fuel tank as

part of the counterpoise—you will create an

explosive hazard!

To connect copper tape to a metal hull, you

need an isolating connector. Use series 316

stainless steel contact points (these can be made

up of 316 stainless nuts, bolts, and washers, all

readily available at any chandlery), and seal the

connection with a water-excluding product like

Boeshield T-9 (www.boeshield.com) or Corro-

sion Block (www.nocorrosion.com).

If your boat is wired to ABYC electrical

specifications, then the through-hull fittings will

already be bonded via a green wire conductor.

If so, you can route the copper tape to the

178 marine electronics installation and troubleshooting

copper foil

backing plate for

below-waterline

ground plate

Copper tape is used to connect the SSB radio antenna to the ground plane or counterpoise. On this

boat the tape is connected to a ground plate below the waterline. The metal plate shown is actually the

backing plate for the Dynaplate ground plane, which is mounted outside the hull, below the waterline.

Dynaplates are “sponges” made of sintered bronze. When viewed under high magnification, this mate-

rial appears as a series of connected small spheres. It is extremely porous and thus exposes far more

metal surface area to the water than its physical dimensions suggest.