I built a 15 meter beam with the DE cut for 21.250. The MFJ analyzer reads 23.000 for a 1-1 match. I added about 8 inches and the best SWR is at 22.500. These tests were made at 10 feet. Will the frequency go down when the beam is at 40 feet? I can't believe that I have to keep adding to the DE. Tom W8JWN