FMD55 1999 Page 3
12.12 Antenna Reception onboard Vessels
Radio receivers are today, standard equipment on board sea-going
vessels.
In most cases it is seldom taken into account, that every receiver, no
matter how expensive it is, can only function as good as its antenna.
What should one take into consideration when choosing an
antenna?
x The frequency range of the antenna must have the same range as
the receiver, at least have the same range that is going to be
used.
x The output impedance of the antenna must match the input
impedance of the receiver. In other words, the antenna and the
receiver must conform.
x The antenna and the cables leading to the receiver should
transmit the least possible interference to the receiver. This entails
proper grounding of the receiver and the antenna.
Receivers used in the maritime sector are usually 100 kHz to 30 MHz,
i.e. are designed for use in the lowest LW ranges to the highest SW
range. This corresponds to a wave range of approx. 3000 to 10
metres, an extremely vast range. Since the ratio of the length of an
adapted antenna is always in fixed proportion to the wave-length, it
is understandable that a long-wire antenna of a certain length can
only be correctly adapted to one single frequency. Therefore, when
using a long-wire antenna such as an insulated back-stay, it is
necessary to fit between the antenna and the receiver cable, a
suitable adapter. Such adapters exist (e.g. MLB marine long-wire
balun), which solve the problem as adapter with a large frequency
range between the long-wire and the shielded lead cable quite
satisfactorily.
The antenna itself should be as high as possible and installed as far
away as possible from local disturbances.
Practically every electric and electronic piece of equipment
transmit interference signals which should not reach the unit via the
antenna. New equipment with corresponding approvals or CE seals
have been designed and constructed, free of disturbance as far as
is possible. Measurements must betaken to make older units free of
interference.
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