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.
--

I use a horizontal omnidirectional antenna for 2M in the truck while
working SSB. Most home-based 2M SSB stations run horizontal
polarization (at least here in the USA). I use it to help avoid the 20
dB or so loss that occurs from crossed polarization.


Ian Jackson wrote:


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.

--
Scott
http://corbenflyer.tripod.com/
Building RV-4
Gotta Fly or Gonna Die

Ian Jackson wrote:

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.

In message , Scott
writes
I use a horizontal omnidirectional antenna for 2M in the truck while
working SSB. Most home-based 2M SSB stations run horizontal
polarization (at least here in the USA). I use it to help avoid the 20
dB or so loss that occurs from crossed polarization.



Same here in the UK. However, SSB is generally associated with longer
distance working (for lots of reasons), and folks tend to have larger
antennas then for local ragchews on FM (often through a repeater). If
you have a large antenna, it's physically easier to make it horizontal
(eg fewer problems with mounting it and avoiding the mast). If you
regularly work the SSB guys, you would certainly want to use horizontal
when mobile, especially as SSB is much less forgiving than FM is to the
deep and rapid flutter that is accentuated by cross-polarisation.
However, I think it's not so much a case of 'wanting' to use horizontal,
it's more like 'having' to.
Ian.
--

"Roy Lewallen" wrote in message
...
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?

Thank you for the reflection explaination Roy- the geometry makes perect
sense.

As for the ground wave- perhaps I am using the wrong term in describing the
regular (non enhanced) communications that takes place on 6M and up.
On 6M I can regularly work out to 300 miles or so w/o the aid of sporadic E,
aurora or other ionospherically propogated signals.
The ARRL Antenna Handbook describes ground wave as:
"...any wave that stays close to the earth, reaching the receiving point
without leaving the earth's lower atmosphere."

Kraus doesn't address VHF ground wave that I can see.

Perhaps scatter mode might be a better description- in this case tropo
scatter.

73,

Dale W4OP

"Theplanters95" wrote in message
...
Have you tried an halo or loop antenna? M2 Antenna's and Par Electronics
makes
them. Homebrew plans are on the net.

The halo is a 1/2 wave dipole bent into a circle. Common designs use 1
turn,
but 3 turn halo's have been used, with more gain. Stacking 2 halo's also
provide additional gain. Weak signal operaters on VHF and UHF use them
mobile
on a regular basis.

Randy ka4nma

Two points of clarification. The PAR design is not a half wave antenna. It
is longer than a half wave- that length combined with the isosceles triangle
shape yields an excellent omni pattern and a bit more BW

The 3 loop haloes were not 3 turns. The loops were configured as a folded
dipole in order to increase the inherently low feedpoint R (10-15 Ohms) of a
single loop. There is no increase in gain from doing this.

Dale W4OP

Dale Parfitt wrote:
The ARRL Antenna Handbook describes ground wave as:"...any wave that
stays close to the earth, reaching the receiving point without leaving
the earth's lower atmosphere."

That definition is very misleading at VHF, since normal tropospheric
refraction takes place entirely in "the earth's lower atmosphere" but
generally doesn't involve ground at all. It's a gradual bending of the
space wave.

Kraus doesn't address VHF ground wave that I can see.

Perhaps scatter mode might be a better description- in this case tropo
scatter.

That isn't quite it, either, because "scatter" has a specific meaning
which doesn't fully apply to this complex (and varying) mixture of
propagation modes. In fact, no attempt to label VHF/UHF propagation as
one single mode can ever be correct.


--
73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek

Dale Parfitt wrote:
As for the ground wave- perhaps I am using the wrong term in describing the
regular (non enhanced) communications that takes place on 6M and up.

From the IEEE Dictionary:

"The ground wave can be decomposed into the Norton surface
wave and a space wave consisting of the vector sum of a
direct wave and a ground-reflected wave."

Looks like you are using the correct term and others may
not be.
--
73, Cecil http://www.qsl.net/w5dxp


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Ian White, G3SEK wrote:

Dale Parfitt wrote:
The ARRL Antenna Handbook describes ground wave as:"...any wave that
stays close to the earth, reaching the receiving point without leaving
the earth's lower atmosphere."

That definition is very misleading at VHF, since normal tropospheric
refraction takes place entirely in "the earth's lower atmosphere" but
generally doesn't involve ground at all. It's a gradual bending of the
space wave.

Yep, the IEEE Dictionary says the "ground wave" possesses a
space wave component. "From a source in the vicinity of the
surface of the Earth, a wave that would exist in the vicinity
of the surface in the absence of an ionosphere. The ground wave
can be decomposed into the Norton surface wave and a space wave
consisting of the vector sum of a direct wave and a ground-
reflected wave."
--
73, Cecil http://www.qsl.net/w5dxp


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Roy Lewallen wrote:

I sense there's still a failure to communicate.

If Dale means by "V/U" VHF and UHF, ground wave isn't a viable means of
propagation anyway.

Maybe you could revise your definition of "ground wave" to
agree with the IEEE? The IEEE dictionary says the "ground wave"
is defined to be what would be left if we took away the ionosphere.
It says the ground wave *includes* a component of the space wave.
--
73, Cecil http://www.qsl.net/w5dxp


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Cecil Moore wrote:
Ian White, G3SEK wrote:

Dale Parfitt wrote:
The ARRL Antenna Handbook describes ground wave as:"...any wave that
stays close to the earth, reaching the receiving point without
leaving the earth's lower atmosphere."

That definition is very misleading at VHF, since normal tropospheric
refraction takes place entirely in "the earth's lower atmosphere" but
generally doesn't involve ground at all. It's a gradual bending of the
space wave.

Yep, the IEEE Dictionary says the "ground wave" possesses a
space wave component. "From a source in the vicinity of the
surface of the Earth, a wave that would exist in the vicinity
of the surface in the absence of an ionosphere. The ground wave
can be decomposed into the Norton surface wave and a space wave
consisting of the vector sum of a direct wave and a ground-
reflected wave."

Thank you - that's a new one to me.

So what does the IEEE define a "Norton surface wave" to be?


--
73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek