RF remote control HELP

Hello everybody. I want to control a few relays at about 1km ( 1000m ) away but the line of sight is blocked by trees. I′m working on the 433MHz tx/rx modules, like the TWS/RWS434 with encoder/decoder ICs, because I′ll be able to have a few receivers with just one transmitter.
I doubt that the tx power would be sufficient so I′m wondering if I could connect the output of the
TWS to the input of a 1 or 2w amplifier. Can you recommend one? any suggestions as to frecuency, transmission method? I′ll have to get stuff from USA, any recommended supplier?
Thanks, Alberto.

If you have mobile network then it would be legal to use GSM module. In most of the places it illegal to use a powerful FR transmitter.

Sorry, forgot to mention; NO communications down there.

Try to use lower frequency like 27MHz.Or increase your output power with an efficient antenna if the max. output power is not constrained.

Electronics Fusions
here you can the circuit diagram and working of 433mhz remotecontrol