There are many things that affect a point-to-point wireless communication: frequency, TX power/RX sensitivity, type of modulation, height of (both) antennas and cable losses, line-of-sight propagation (especially Fresnel zone), and last but not least, the antenna types and their polarization.
10km may not look as a very long distance for a wireless system, but if some (or all) of the things mentioned above are not carefully chosen, the quality of the communication may not be as expected.