[OnlyMortal]

For detecting at a distance, it’d depend on the quality of your receiving system. The electronics in a radio make noise themselves.

A kilowatt won’t get far - the signal strength decreases over distance. I seem to recall CB radios with an amplifier could easily attain that.

No doubt someone here could calculate the theoretical wattage needed to appear above the background noise on, say, Proxima Centauri.

[signalioto]

Does it decrease due to the wave getting bigger or due to background noise getting louder?

Then a laser is a better choice?