1/4wave GP. 10/12m fit a 5m mast. 15m just fits a 6m mast. This is for the classic arrangement with 3 radials sloping down from the feedpoint to ground at 45degs (use Pythagoras and basic trig to work out lengths and angles). In mine, the radials meet the ground.

NIST’s WWV time signal uses 1/4wave GP antennas. Each antenna is 1/2wavelength tall. The top 1/4 is the radiating element, the bottom 1/4 is isolated and used to raise the radiating element 1/4 wavelength above ground. There are 9 equal length radials, each of which slopes down at 45deg, each radial is sqrt(2)/4 wavelenth long. This is a little longer than the classic formula which suggests 1/4wavelength long (WWV length 0.3535 wavelength vs 0.25 wavelength). Antennas are fed with hardline coax and no coax crosses another coax feed.

That’s a commercial setup. The improvement of 9 vs 3 radials is measurable but probably not worth the effort for SOTA.

I’ll post some pics/measurements for mine.