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how does marine vhf antenna work?
"Meindert Sprang" wrote in
: These antennas are half-wave antennas and they don't need a counterpoise. Only a quarter-wave antenna needs one, to account for the other missing quarterwave part, so to speak. Meindert The big antennas are phased arrays of cheap little wires encased in fiberglass to protect the wires and make them look "bigger". There are a series of dipole antennas inside the long ones with phasing networks to make them work together to produce a flattened pattern from the halfwave dipole's radiation donut pattern. If you step on a donut, it gets wider and that's what the phased array does to the radiation donut of the halfwave. Unfortunately, the squished donut is always perpendicular to the plane of the whip so when the boat is heeled over or rocking around in the waves, too much gain from too many phased dipoles is a bad thing. The flat donut on one side of the boat is pointing into Davy Jones' Locker and the other side of the boat it's pointing to space, not the target. Halfwave antennas, like the Metz, with fat donuts and wider radiation patterns are better on sailboats and small boats for that reason. |
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