RadioBanter - View Single Post - E/M radiation from a short vertical aerial

Spike[_3_] · March 8th 15, 08:40 AM posted to rec.radio.amateur.antenna

On 08/03/15 00:17, wrote:

True ground wave, which to me, is the same as the surface wave,
actually can follow the curvature of the earth, which a space wave
cannot do. But true ground or surface waves are generally only
taken advantage of on the lower frequencies such as MW, or LW.

That's true, which is a shame as useful ground-wave/surface wave can be
had on 28 MHz; a maximum range figure for a path over ground of average
conductivity might be 25 miles, and considerably more if the path is
over water (especially sea-water).

But they can be used likely as high as say the 40m band in some
cases. I used to have a fairly stout ground wave on 40m when I
ran a high ground plane. And I think part of that energy was acting
as a surface wave and following the curvature of the earth.

The reason I think so, is because the distances I could work with it
were a good bit farther than what I would expect with the space wave
alone.

Maximum surface wave over ground with average conductivity might be 40
to 45 miles on 40m; if you were getting ranges over this, then your
ground conductivity might have been enhanced, or due to the height of
your ground-plane, you could have experienced refraction of the space
wave. If your location was on a hill-top or other high ground, this
could have helped the space wave refraction as well.

And I could use the space and surface wave in that case, no matter
what time of day or night, or regardless of the conditions needed for
sky wave between the two locations. So lots of times during the day
when the MUF dropped low enough to lose those people who were 100-150
miles away via sky wave, I was still able to work them via the ground
wave. The people using the dipoles and such could hardly hear a peep
out of the ones I was working in those cases.

I believe that the availability 24/7/365 of the space-wave and
surface-wave is one of Amateur Radio's undervalued assets. On 160m the
surface wave might reach over 100 miles, including behind hills and into
valleys, which here in the UK would enable a station to reach a
significant proportion of the UK Amateur population. Unfortunately,
people dismiss verticals in favour of horizontals of one form or
another, the usefulness of which drops to zero when the sky wave
disappears (apart from any vertically-polarized radiation from a
mismatched feeder or unbalanced elements).

Thanks for your interesting observations.

--
Spike

"Hard cases, it has frequently been observed, are apt to introduce bad
law". Judge Rolfe