2-10
Chapter 2: Installation
98-144591-D
Grounding connections
2.3.3 Minimizing ground loops
By routing the coax cable very close together with the ATU grounding strap (i.e. secure good RF cou-
pling between the two) all the way down to the ground-plane, there will be no RF ground loop left to
generate any interference.
ATU
TU
CU
coaxial cable
Ground-Plane
OK installation
Zg
Vg = Iant x Zg
2.3.4 Antenna start
The vertical antenna always "starts" at its electrical ground-plane, whether or not it is physically mounted
there. First determine the antenna’s electrical ground-plane, which is where the ATU should preferrably
be installed. Where possible always take the ATU to the ground, not the ground to the ATU.
In case of a fi breglass boat, the ground-plane may well be at the hull grounding terminal. Then this will
be where the antenna actually "starts" and hence where the ATU preferrably should be installed.
ATU
TU
CU
OK installation
Not a 'Hot' Handset
Ground-Plane
The antenna starts here
2.3.5 Antenna Tuning Unit
It is of the utmost importance that the ATU grounding connection provides the lowest possible RF-
impedance. Losses in the ground connection will result in a decrease in radiated power which means
that the range of the transmitter will be reduced.
For ATU grounding in steel ships a 100 x 0.5 mm copper strap is connected between the ground terminal
at the bottom of the Antenna Tuning Unit and the Antenna Mounting Kit welded to the superstructure
or, if not using the ATU Mounting Kit then to two or three ½" or M12 bolts welded to the superstructure.
The length of this copper grounding strap should be kept as short as possible within app. 0.5 m in order
to ensure that its RF impedance remains within reasonable limits.
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