michel wrote:
That is some clear information!! The 5/8 wave version needs a shorted stub
as well?

What we are looking for is the length of a series
matching stub section that will bring the system
to resonance, i.e. we are looking for the current
maximum point.

The graph at http://www.w5dxp.com/majic.gif
gives the length of the series matching stub
section for dipoles of various lengths from
1/2WL to 1.5WL. The graph can be used for
monopoles by doubling the monopole length.

For instance, doubling the 5/8WL monopole length
gives a 10/8WL dipole length which is 1.25WL.
A 1.25WL dipole needs a series matching stub section
of 0.19WL, i.e. the bottom stub on a 5/8WL J-Pole
needs to be 0.19WL. Make it a little too long and
trim for resonance.

If you double the 1/2WL monopole length of the
J-Pole you get a 1.0WL dipole. From the graph,
a 1.0WL dipole needs a 0.25WL series matching
stub section, i.e. the bottom stub on a 1/2WL
J-Pole needs to be 0.25WL. Of course, that is
the standard J-Pole design.

If you happened to want to design a 0.35WL J-Pole,
the series matching stub would need to be 0.33WL
long. 2(0.35WL) = 0.7WL

Let me know if you understand the graph.
--
73, Cecil http://www.w5dxp.com