Up until now, most hams have found it very difficult to make contacts of 500 miles or less on 20 meters. Most hams resort to using 40 or 80 meters for these distances. This is true even though they are using a wide variety of antennas, at a wide variety of heights. I look forward to seeing your results to break this long streak of failure. When you have your antenna for reliable 500 mile paths on 20 meters (or better yet, 15 or 10 meters), please post your results, as I would be interested in constructing such an antenna myself. It can't be all that difficult, and I for one am confident that you will be the one to finally pull it off.