Dave Shrader wrote:
Z is close to +58-j138 ohms.

A small inductor of 0.88 uH in series with the antenna should provide a
pretty good match to 50 ohm coax.

Larry D wrote:

I want to construct a 5/8 wave ground plane for 24 MHz.

Wow, after all that, a simple answer. Thanks!

The reason I wanted to try 5/8 wave is because I have had
the Solarcon A99 1/2-wave ground plane for 10 meters up
for about 5 years, and it is an excellent antenna for DX. This
is, according to the product blurb, a "1/2 wave, voltage-fed"
design.

The radiation patterns in the antenna book give the
impression that 5/8 wave should be "even better" for DX.

Of course, a lot of that performance had to do with who is
on 10 meters in the first place, and conditions over the past
5 years as well.

It is finally falling apart (radials coming loose,) and the
prospects for 10m in the next few years don't look so good.
I wanted to switch to a similar antenna, but for 24 MHz.

I notice that some of the answers here were geared toward a
ground-mount, which is not what I meant by "ground plane,"
this antenna will be at 30', and probably will have full-size,
1/4 wave (?) sloping radials.

As it turns out, at the antenna forum in Dayton, Dean Straw,
the author of the ARRL antenna book, talked me out of using
5/8 wave. He feels that it will not appreciably enhance DX,
compared to 1/4 wave.

He also talked me into getting the latest version of the
antenna book, which alas, still does not mention doing what
you suggest, not even in the VHF section, as one person
mentioned, but at least I have the answer now. Thanks again.

Larry DiGioia N8KU