You have many problems to over come, first off is the legal aspects, what you are wanting to do is probably illegal almost anywhere - unless you can obtain a licence to do it?.
Next your frequency, this is probably far too low for the bandwidth you're looking for - you need to go much higher.
Distance - 1km is a fairly long way, again it's unlikely that you can get a licence to do it!.
Protocol - you can't just squirt plain RS232 across a radio link.
I would suggets you look at licence free radio modules, you can get some in the km range, but not that will do 115kbps.
The 555 idea is far too crude!.