the simplest way of building such a choke will be using a #31 material toroid to wind a "guanella" choke over the coax cable, the instructions to build such a choke can be found here
After you verify all is well with a power meter check at both the transmitter and load ends of the cable, weather proof all outside connectors with coax seal or 2 layers of vinyl electrical tape. Secure the cable up the tower at different distances to minimize mechanical resonances that can...