We are developing a project that involves water level data acquisition from a remote sensor about 2.5km away.
The modules, hooked up to a 14dBi patch antenna, do not communicate when separated at 2.5km. But when they are moved closer to about 1.5km range, they are able to communicate. And heres the interesting thing, now, if we separate the modules further, LOS maintained and power uninterrupted, they communicate well upto 3km. Maybe even further but we haven't tested beyond 3km.
So is there a parameter configuration we are missing maybe such that the modules require initially to be within an optimum range and then only separated to further distances.