In terms of percentage of frequency the 80m band is quite wide. Few antennas will provide a low SWR to a random length of transmission line over the entire band. Here are two antennas which will do just that and one of them will even provide 3 dB of gain over a dipole. Broadband 80m dipole, 747 kb, QST July 1995 and Improved double zepp , 2,581 kb, Antenna Compendium 4