(Sorry about the use of "diff", but I needed the characters.) In air, a half-wave dipole can be physically trimmed to resonance and will radiate well. It can also be tuned using a pi network to resonance and will also radiate well. In fresh water, the same dipole needs to be trimmed to approximately 1/9 the length to resonate. It also can be tuned to resonate using a pi network, leaving the length the same as in air.
What would be the difference in operational range underwater between the two approaches?
My question was more general about optimizing the ERP via trimming verus tuning and I was using the dipole as a well understood reference. Experimentally, I have trimmed a 1/4 ground plane underwater, using a VNA and it's trimmed length in air was reduced from ~3cm to ~2cm. This was done in a small air filled glass jar using the metal lid as the counter poise. Although I have tried to, I assume I could have instead tuned it to resonance, again whilst underwater using a pi network and minimizing the reflected energy. As actually measuring the operation range of either approach is quite difficult, I am wondering what the approximate difference would be in general terms?
Specifically I am developing a underwater (fresh not salt) for communicating only a short distance (50cm) using Bluetooth transceivers.
I would be most interested in learning more about magnetic loops. A big challenge with these is how to go about tuning these underwater?
Another important experimental need is what to employ for an underwater antenna that would have known or calibrated characteristics such as gain, and directionality UNDERWATER.