Vertical dipole for 20m (T2LT style).
It’s a great antenna, and the satisfaction you get from using something you made yourself is great.
So if you fancy having a go at making one, your need approximately 17m of RG58, a 68mm diameter drain pipe for the air choke former.
The length of the exposed dielectric is 5.1m plus 30cm for tuning (5.4m total), then 5.1m of untouched coax to the air choke, which is 24 turns of the coax around the 68mm drain pipe.
It’s just over 10 metres in length when made, so you will need something like a 12m spider-beam mast to mount it on.
SWR figures I get are 1:5:1 across the entire 20m band.