Icom AT-140 instruction manual Coaxial cable, Ground and counterpoise

ANTENNA SYSTEM 1

■Coaxial cable

Insulate the lead-in cable of the AT-140 antenna ter- minal and antenna element from other metal objects.

To prevent interference, keep cables as far as possi- ble from an antenna, electric pump and other elec- tronic equipment.

To prevent erroneous indications, keep cables as far away as possible from the flux gate compass.

Use suitable noise filters for alternators, fluorescent lights, etc. Ask your Dealer for details.

■Ground and counterpoise

Why a ship’s ground is required

The AT-140’s ground terminal MUST be connected to your ship’s ground. Grounding prevents electric shocks, interference to other equipment and other problems. Grounding also ensures effective signal transmission.

DANGER! NEVER connect the ground terminal to the following points. These connections may cause an explosion or electric shocks:

–Gas or electrical pipe

–Fuel tank or oil-catch pan

Counterpoise

If your ship is made of FRP, etc. and a good ship’s ground is not available, connect a counterpoise.

1⁄4λ radial for each band

Ground terminal

AT-140

IMPORTANT! The mounting plate is NOT con- nected to the AT-140’s internal ground.

Ideal ground points

One of following points is ideal:

–External ground plate

–External copper screen

–External copper foil

1⁄4λ (quarter wavelength) radial for each band is suit- able for a counterpoise. Install the counterpoise di- rectly below the AT-140’s ground terminal. Insulate the ends of each radial from other metal objects. Lay- out the radial horizontally and as straight as possible.

L : Counterpoise length for the operating frequency [m]

f : Operating frequency [MHz]

Good ground points

If electrically connected to sea water, one of the fol- lowing points is usable:

–Stainless steel stanchion

–Through mast

–Through hull

–Metal water tank

Undesirable ground points

AVOID the following points, if possible. These con- nections may cause noise or electrolysis:

–Engine block

–Ship’s DC battery ground

Electrolysis

All ground cables from the AT-140, HF transceiver, etc. on your ship should be connected to only 1 ship’s ground.

AVOID connection to 2 or more points. Voltage dif- ference between 2 or more ship’s grounds may cause electrolysis.

AVOID connection between dissimilar metals where an electric current is present. These connections may cause electrolysis.

L =	300	⋅	1
	f		4

[Example]

At an operating frequency of 16 MHz, use a counter- poise with the following length:

L =	300	⋅	1	4.7 [m]
	16		4
1 m	39 inches

Ground cable

For best results, use the heaviest gauge wire or metal strap available. Make the distance between the AT- 140’s ground terminal and ship’s ground as short as possible.

Supplied ground cable can be used for ground con- nection to a through mast. Confirm that the through mast is electrically connected to sea water.

RWARNING!— When grounding to metal hull Use a Zinc anode to protect the hull from electroly- sis.

Ask your technical dealer, installer or refer to a tech- nical book, etc., for RF ground details.

2