This is a bit more complicated than expected.
This is a ground plane antenna tuned to the 15m band. It is mounted on a little stand (which I had) with the 4 radials elevated but their ends touching the ground. Each radial is 2m70 (so quarterwave). The ground is a bit wet, therefore should be conductive. Te top radiator has a coil to reduce its length a little bit. SWR is about 1.
Build a small dipole for the 15m band today.