In message , Robert Smits
writes
Thanks for all the suggestions.

I'll see what it's like with 50 ohm coax first, and then make other changes.

What about making the antenna somewhat longer than a quarterwave (which
presumably is what it is)? This will make the feedpoint impedance higher
resistive, and inductive. Make it long enough to get the resistance
close to 50 ohms, and then add series C to cancel the inductance.
--
Ian