This variation on the W3DZZ trap dipole gives lower SWR on the HF bands.
The system is resonant on approx 3.7, 7, 14, 24 7 28.5 Mhz. The top section of the antenna has a half wave between the traps on 7.05 Mhz. The overall top length needs to be approximately 32.9 Metres. Depending on location, height, and overall geometry, the end lengths need to be adjusted to give a reasonable compromise on the desired operating frequencies on the 20 and 80 Metre bands.