This spring I constructed a 20/40m fan dipole and hung it up in the my backyard. I cut the lengths of each element according to the standard formula (234 / design frequency = each dipole side length in feet), and left some extra on each side for tuning. SWR was under 2:1 for both 20m and 40m, but there was definitely room to improve. Today I was able to spend some time taking measurements and tuning the antenna.
I used the excellent SWR Plotter program by K9DUR that automatically transmits across a selected band and records the SWR measured by my Flex 5000a radio.
After the initial measurements showed that the 40m element of the fan dipole was tuned too low, I folded back about 6” on either side.