The pulley system is probably the best way to go as others have noted. As an option, perhaps, I use springs selected from Home Depot that are about 6 inches long. I put a loop of dacron between each end of the spring just in case of failure.
They are installed at each end of the supports between two trees. The spring rate is subjective as you don't want it to stretch too easily or be to stiff. On my property, I have an endless number of trees so I try to use the largest trees which will sway less to minimize stress on the installation. And, I use fishing arrows (which have weighted tips) with a bow to shoot fishing line into the trees then 100 lb nylon line to pull up the dacron rope. This has worked quite well for over 20 years for me. Jim, K1PX _________________ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector