Note....... I have tested my Futaba 6ex 2.4ghz out to 1.75 miles with no problems, but it probably can not do 4 miles. The idea is to fly the UAV out of transmitter range autonomously. This is for sure illegal and this video system is hypothetical and has not been tested. So um... I don't endorse it.
I am planning to use this setup for a school project UAV.
I hope this can save other people from searching the internet for hours on end for the best deal.