Re bille1319
Quote/...Well then you will need a unit that's about 4 times as large to give more power output and longivity. But 25NM range: dream on unless you're talking of equipment capable of transmitting to submarines which is massive i.e Rugby." .../unquote.
You may have mixed up audio, albeit of high frequency, such as a pinger, bat or dog whistle makes; with electromagnetic radiation, which is radio.
The Rugby installation of aerials for GBR on 16 kHz was for electromagnetic ie radio transmission. Initially for long distance communication (before short wave was used) and more recently submarine communication.
Cheers!