Icom AT-140 Instruction Manual - Coaxial Cable
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1
ANTENNA SYSTEM
n
Coaxial cable
Insulate the lead-in cable of the AT-140 antenna termi-
nal 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 or fluorescent
lights. Ask your dealer for details.
n
Ground and counterpoise
Why a ship’s ground is required
The AT-140’s ground terminal
MUST be connect-
ed to your ship’s ground. Grounding prevents elec-
tric shocks, interference to other equipment and other
problems. Grounding also ensures effective signal
transmission.
R DANGER! NEVER
connect the ground ter-
minal to the following points. These connections may
cause an explosion or electric shocks:
• Gas or electrical pipe
• Fuel tank or oil-catch pan
IMPORTANT:
The mounting plate is
NOT connect-
ed 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
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
These connections may cause noise or electrolysis:
• Engine block
• Ship’s DC battery ground
Electrolysis
All ground cables from the AT-140 or HF transceiver
on your ship should be connected to only one ship’s
ground.
DO NOT
connect to two or more points. Voltage dif-
ference between two or more ship’s grounds may
cause electrolysis.
DO NOT
connect between dissimilar metals where
an electric current is present. These connections may
cause electrolysis.
Counterpoise
If your ship is made of FRP, etc. and a good ship’s
ground is not available, connect a counterpoise.
Ground terminal
AT-140
1
⁄
4
λ radial for
each band
1
⁄
4
λ (quarter wavelength) radial for each band is suita-
ble for a counterpoise. Install the counterpoise direct-
ly below the AT-140’s ground terminal. Insulate the
ends of each radial from other metal objects. Layout
the radial horizontally and as straight as possible.
L : Counterpoise length for the operating frequency [m]
f : Operating frequency [MHz]
L
=
300
f
1
4
×
[Example]
At an operating frequency of 16 MHz, use a counter-
poise with the following length:
L
=
300
16
1
4
4.7 [m]
1 m
39 inches
×
Ground cable
For best results, use the heaviest gauge wire or metal
strap. Make the distance between the AT-140’s ground
terminal and ship’s ground as short as possible.
The supplied ground cable can be used for ground
connection through a mast. Confirm that the mast is
electrically connected to sea water.
R WARNING!
— When grounding to metal hull
Use a Zinc anode to protect the hull from electroly-
sis. Ask your technical dealer or installer, or refer to
a technical book for RF ground details.