Underwater antennas

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Underwater antennas

Postby znigel » 03 Feb 2005, 13:05

We wish to transmit CW/AM signals at 60kHz from a unit that will be under water to the receiver at surface (in a boat above transmitter more or less) The 'antenna' we have to use is a 1.5mm-2mm unisolated stainless steel wire that is connected all the way from the transmitter to above surface. How do we approach the problem of connecting the wire in the transmitter (connect with loading coil?) for the most effective transmission. (We know that this concept don't have any good transmission parameters, but we must try to get the best out of it).
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Underwater Antenna/Transmission Line

Postby admin » 03 Feb 2005, 13:40

1) Will the stainless steel wire function as an antenna to radiate electromagnetic energy in the water or function as a transmission line to transmit a signal to the portion of the wire that is above water?

2) What is the purpose of having the wire extend above the water surface if the purpose is not to radiate an above-surface signal?

3) How far will the wire extend above the surface of the water?

4) Will it be possible to establish a ground connection, either directly to earth or by means of a counterpoise at the transmitter end?

5) What will the length of the stainless steel wire be?

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Re: Underwater Antenna/Transmission Line

Postby znigel » 04 Feb 2005, 12:59

Answer1) The steel wire is used as an antenna. See picture on "ht..://goto.glocalnet.net/fajs"

Answer2) The wire is connected in the boat. it's a part of a downrigger. See same picture

Answer3) About 0.5metres on a roll

Answer4) No, not as we see it. Since the transmitter will always operate below water surface and the receiver will be situated in the boat.

Answer5) variable from 0-30m (the length of the wire in water is depending on how deep the down-rig is supposed to operate.)
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Re: Underwater antennas

Postby sparky » 13 Nov 2010, 21:29

About all you can do in a case like that is apply RF voltage between the boat (if it is metal) and the wire underwater antenna. However, the water will effectively short-circuit the antenna back to the boat and the amount of radiated RF energy will be extremely small regardless of how the antenna is coupled to the transmitter.

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