I need to create an AM modulated carrier of 25 Khz that is highly
focused in beam width. I am aware of part 15 and will not be using
this for any other reason than for research. I need a range of 50
feet. Receiver will be a tuned resonant tank with about 90 db of gain
post detection. I would like to be able to "focus" this beam but being
in optics I have no idea of how one might control the dispersion of a
carrier like this. In other words in my field I can collimate or focus
a light beam but dealing with this wavelength I have not a clue!

Thank You in advance for your input

Steve Sands