I haven’t tried any radials, and tbh I’m not certain to where I would attach them given the j-pole design has a matching network in-built. I’ve got a 1:1 balun at the feedpoint and an inline choke at the radio. My 10m antenna of identical design is great, and this one is great too (I see ~1:1 at 14.250), it’s just much higher in the band than I had planned and I strongly suspect it’s simply ground reflection since the radiating element is way lower than the halfwave it ought to be.