In message , "Ian White, G3SEK"
writes
Roy Lewallen wrote:
Dale Parfitt wrote:
I wasn't talking about skip either- the majority of V/U weak signal
work is
extended ground wave via perhaps enhanced tropo.

Ground wave? Really? I admit I'm not a propagation expert, so I'd
appreciate an explanation from someone who is. Is there really enough
ground wave propagation at VHF/UHF to be useful for any purpose, even
short range communication?

No, it isn't ground wave at all. It's just a loose way of saying
"normal short-range VHF/UHF propagation" which is a complex combination
of line-of-sight, diffraction and scattering.

At medium ranges - which can be several hundred miles between
well-equipped stations - atmospheric refraction and scattering are the
main mechanisms. When weather systems lead to an "opening", signal
strengths and workable ranges are enhanced by much stronger refraction
and ducting.



When I was a lad, I learned that the 'goundwave' requires the flow of
current in the ground, and is intimately tied up with the ground
conductivity. Its attenuation rises rapidly as frequency increases, so
is essentially only a low-frequency phenomenon. It requires a vertical
antenna.

Propagation at the higher frequencies is via 'spacewave', which has
nothing to do with currents flowing in the ground.

Many years ago, there were lots of discussions about whether vertical or
horizontal polarisation went further. In the UK, many of the (no longer
used) VHF TV transmitters used vertical. I don't think that the US ever
used vertical for TV. I think that the verdict eventually was that
horizontal won by a very short head.

At UHF, horizontal is invariably used for the high power TV
transmitters, and the low-power fill-ins nearly always use vertical.
There is therefore little opportunity to make a practical comparison of
which polarisation is consistently received at great distances - it's
always horizontal.

As for short range mobile and portable communications, propagation
relies so much on 'bouncing off things' that it probably doesn't matter.
Circular is probably best, but vertical physically easier. I can't
imagine why anyone would want to use horizontal.

Cheers,
Ian.
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