Path loss at 2.4 GHz
Free-space path loss at 2400 MHz is about 120.1 dB over 10 km, 15 dB more than at 435 MHz. The same transmitted power therefore arrives far weaker, and antennas must make up the difference: a pair of 24 dBi dishes gives 48 dB of gain, enough to make a 10 km link comfortable even with a few tens of milliwatts. Legal limits on radiated power apply and differ by country, so check the local rules before building.
Clearance is everything
At this frequency diffraction around obstacles is small. Keep at least 60% of the first Fresnel zone free: for a 10 km link the radius at the middle is about 17.7 m, so about 10.6 m must be clear of trees, roofs and terrain. Use the Fresnel zone calculator and read line of sight versus diffraction. On a long link also remember the curvature of the Earth: the bulge in the middle of 10 km is about 1.5 metres with the standard k factor.
Check the path
Put both ends on the coverage map, choose 2400 MHz and the Wi-Fi mode, and look at the terrain profile: it shows the first Fresnel ellipse and the most obstructive point of the path. Buildings and trees are not in elevation data, so always add a margin on site.
