Posted by Alex Pettit on SARA Mailing List 18/1/2026:
Typical calculation for a one quarter wavelength (1/4 WL) antenna is WL / 4 * 0.95
211 /4 * 0.95 = 50.11mm ..
The diameter of the wire creates a bit of ‘capacitance hat’ effect & in my case, using a 4 mm diameter brass tube changes that to 49mm.
FYI, on my folded 20 meter dipole ham antennas, I used to tune/trim the lengths to 1cm : That equals 0.1mm on a 0.211m feed.
Alex