It is not rocket science, but they work very well. And they are simple to construct.
It would not work that far without the omni directional collinear antenna at the access point. It is also important to put the power and network cable at the top of the tower. Or you could use DC power and put solar panels and a battery at the top of the tower. Feedline loss is serious issue when you only have very low power to work with.
So minimize feedline length and maximize gain on both ends. The 4 mile path I was using is line of sight. At 2.4 GHZ and this low of power level it would have to be line of sight to work.
Where I lived in NM we had a remote base on a 9020 ft. mountain top. Nearest power was 2-1/2 miles away. We went up in the winter and collected snow and melted it for water to pour cement base for tower. The hole in the mountain top was dug with hand steel and explosives. It was totally solar powered, with batteries, cavities and RF components in 2 55-gallon barrels buried to ground level with 6” of foam under lid. Only things above ground were tower, Phelps Dodge super stationmaster antenna and solar panels. The remote drew 60 ma quiescent current in standby. The batteries were 2 deep discharge marine batteries. It would cross-link from UHF to VHF and from VHF to UHF remotely. It used ICom IC-2 and IC-4 wired to the controller for programming. The repeater itself used a Repco transmitter and receiver.
At the time it was built, there were 3 like it working in the state. I loved those days.
I remember setting in a restaurant in Deming NM and listening to the up down link of the Shuttle missions from JPL in CA over the Cactus Net (remote base group spanning from LA to Las Cruces NM). We could listen to the repeater on a hand held and during the mission if the repeater was not in use it was piped in. Line of sight radio from the West Coast. Amazing stuff.
Imagine, in the early 1980's walking down the street in Las Cruces NM, talking on 2 watt handi talkie and working another ham in California, on line of sight radio frequencies. Amazing times. (Pre cell phone and internet)
No, I was just curious about what was possible.
At the time it was built, there were 3 like it working in the state. I loved those days.
It sounds like work you could be proud of, and a lot of fun.
Thanks.