This would also work as an occasional alarm for me, because there are a lot of pirate radio stations in my part of the world. It would go like: static noise - sudden silence - guy shouting "Hello?! Test one, two!" - horrible music.
When i was very young i tried to setup a small radiostation , but only could do it for small radius and never perfected it. Do you have idea how can I do this ?
You need a transmitter (oscillator + modulator) and an amplifier to get any reasonable range. Also (maybe even more important) some good antenna cable and an antenna tuned for your frequency. Without the right antenna you'll never get a decent range.
I realize you're probably doing it for yourself, but as someone who's had neighbors who don't care that their dog is a noise nuisance, I appreciate you.