Well, I was about to say don't bother and save your money until yesterday when I tried my E11 sub fitted with Radiometrix 27Mhz modules with the latest version of the underwater antenna. It actually worked quite well. So it shows promise, I would say.
This photo shows the underwater dipole with an overall length of 534 mm. The foam, in the middle, covers a 1:1 Choke Balun on a ferrite ring. I have used foam to try and avoid putting the Balun in a bulky, waterproof box. A blue LED at the stern is triggered by a "surface planes" command.
I am very grateful to Rob Schuckman for pointing me in the right direction:
Rob recommends using a trimmer capacitor. But as a very rough initial trial I put a 22pF capacitor in one leg of the dipole and this seemed to improve matters (range, glitching etc). For approaches to a more precise approach see the end of this post.
This gives an idea of the range (on the surface but with antenna immersed.)
This photo perhaps shows the direction of future development - the use of a nanoVNA to optimise the underwater antenna:
(I managed to measure and store "S Parameters" for this antenna in air and water. If anyone would like to have these (and hopefully understand what to do with them more than I do!) then please PM me.
Various video clips showing yesterdays trial. (The trials were untethered but without diving. Small steps! ) :
My Arduino software version I am using is here:
Radiometrix-RX-3.8 and Radiometrix-TX-3.2 are the current versions.
Sorry Geofrancis, I forgot to give the ordering information for the modules. I phoned:
Sales & Admin Department
231 Kenton lane
Tel: +44 (0) 20 8909 9595
The modules are not cheap and I wonder if the project could be done more economically by purchasing a TX module (which gives the advantage of CE approval) and using it with a cheaper RX ?
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