I've been using the original Fritzel FD-4 OcF for 10 years or so, 1500 watt version with 1:6.6 balun and incorporated 1:1 choke.
Added coil and length of wire on the short end to resonate it on 1850 so it is working on 160 as well, coil was 180 microH and length of wire after that about 7 meters, cut to resonate on 1850.
Original FD-4 lengths : Fritzel used the shown dimensions of 13.8-m and 27.7-m in the 1960s.
That way i added a band, you can add more bands by just adding 1/3 and 2/3 lengths for the band(s) you want to add like the fan dipole.
https://www.eham.net/reviews/detail/1055
For more details on the OCF look here: https://pa0fri.home.xs4all.nl/Ant/FD4/fd4eng.htm search the FD-4 and read up.