gate mechanism remote control

Hi to everyone, I'm a installer for automatic gate mechanisms, and sometimes have problems with the operating distance between emitter and receiver, due to average distances 100-150m, open field, things use to be ok at the first 1-2 year operation, after this time people start to complaint about miss operation of gate's remote control, only opens the gate if one operate the remote near the gate, also I already had confirmed, this is not a remote battery problem, I was wondering if someone know some kind of preamplifier module for 443.92 MHz frequency which is the one for these systems, or other idea to solve this problem, many thanks. vitorman@gmail.com