Hi i'd like to know how far i can run a rg8 coax cable to a outdoor antenna and not lose the uhf signal thanks?

RG8 is a 50 ohm cable. Outdoor antennas and TV tuners are 75 ohm so you definitely do not want to use RG8. RG11 would be suitable but it's bulky and hard to work with. RG6 is the cable most used today and if you put a UHF preamplifier at the antenna you will overcome the losses of the coaxial cable feed line. If the antenna you have does not have a 75 ohm output you will need a 300-75 ohm balun feeding the preamplifier.