The QRPer Board

I'm referring to the so-called "Rybakov antenna"

https://wb3gck.com/2018/12/09/revisitin ... -vertical/

a simple and easy to build vertical antenna offering good performances over the 10...80 meters bands.

Also, a good field of ground radials and/or stakes will definitely improve the performances

as for radials, four of them will suffice for a simple portable setup; the lenght will be 5.20m (17ft) and 2.15m (7ft) the reason for those sizes is simple; 5.20 meters is near to 1/16 wave on 80, near to 1/8 on 40 and 1/4 on 20; so on all the bands between 20 and 80 meters it will offer a low impedance path to RF "return" currents do your math with 2.15m for the "upper" HF bands notice that those lenghts are ok with "random" endfed too

just in case

((300/3.5)/16)=5.35 we repeat the calc for 40 and 20 meters and "round" those 5.35m to a lower value to fit the other bands too by the way we don't want to shorten the wire too much or it will be uneffective for our purpose (which is also to avoid common mode currents on the feedline)

I build a K6ARK variant (15' radiator, 7.5' radials). Just waiting for better weather to test it.
The question is how a Rybakov compares to a 19'/17' EFRW?

it depends see, as a matter of fact a vertical offers lower takeoff angles so better DX performance, but if one is going for mid-distance or local, then an endfed installed as an inverted vee would offer good NVIS performances

as for the EFHW, this one

https://www.aa5tb.com/efha.html

works well, but I prefer EFRW antennas for their ability to cover more bands