Antennas - Underwater

I have been having some wide-ranging discussions with Rob S from Holland about 27MHz but also underwater antennas. He has been very helpful and recommended this paper (Google this phrase and you can download the whole paper):

Antenna Design for Underwater Applications by Oluyomi Aboderin

It is a long and often technically complex paper but he recommends Chapter 2.5 for a good historical review and the section starting on page 111 gives details of antenna mounted on the outside of the hull or WTC.

The diagram on Page 111 shows the general idea - a dipole mounted on the outside and insulated from water by a thin covering.

You may wonder what the advantages may be? Well space saving is one. Also the antenna can be much shorter (i think he said 1/10 of the length in air.) This would have particular advantages for 27MHz.

We need to do some practical experiments to see how these work out - not too difficult to build, I think.

Rob recommends dipoles.

David
M7DYP

A further discussion with Rob gives some clarification of the benefits from using antenna immersed in water. (i.e not just placed in air inside the WTC)

He stressed that the main benefit is reduced antenna length and this is only important for the lower frequencies we use 75/40/27 MHz. For something like 433MHz the antenna would become tiny and impossible to tune.

David