Jouko, OH5RM wrote:

Take 20m of wire, that is half of a dipole.
Put a 1/4 electric wavelength shorted stub for 10,1MHz so that the open end
is 7,25m from center and the shorted end pointing to the tip of antenna. One
side of stub is the 20m wire itself, like in the upper picture.

I did just that with EZNEC, but with a free-space dipole. Without the
stubs, the antenna resonated at 3.6 MHz. With the stubs, that dropped
to 2.75 MHz and additional low-impedance points were noted at 6.5 and
11 MHz. The patterns at 2.75 and 6.5 had the desired dipole shape,
but the 11 MHz pattern had multiple lobes.

Jim Bromley, K7JEB
Glendale, AZ, USA