Greetings to all the antenna experts here!

I want to create horizontally polarized antenna, low profile, located above
large ground plane. And I need it to be omnidirectional (sort of) and have
sufficient gain in horizontal plane.

My frequency of interest is 900 MHz. The ground plane is a roof of a car.

I tried loops, from 50 to 300 mm diameter, radiation goes up if I mount it
above the ground plane.

Any ideas?

Thank you,

Andrey

"Bill Turner" wrote in message
...
On Sat, 4 Sep 2004 14:57:09 -0700, "Andrey"
wrote:

Greetings to all the antenna experts here!
I want to create horizontally polarized antenna, low profile, located
above
large ground plane. And I need it to be omnidirectional (sort of) and
have
sufficient gain in horizontal plane.
My frequency of interest is 900 MHz. The ground plane is a roof of a car.
I tried loops, from 50 to 300 mm diameter, radiation goes up if I mount
it
above the ground plane.
Any ideas?
Thank you,
Andrey

__________________________________________________ _______

FWIW, horizontal polarization at 900 MHz won't get you far. Vertical is
preferred because horizontal is rapidly absorbed by ground loss. On the
other hand, if you don't *want* to get very far, use a vertical and just
reduce power.
This will be sad news to all the V/U weak signal ops who have consistantly
covered long distances using horizontal polarity.

Dale W4OP

To Bill Turner,

my tests showed no difference between Horizontal and Vertical propagation.
Vertical is quite busy here, lots of interference. Horizontal, on the other
hand plays much better.

My question was antenna design, not the propagation issues. Thanks for
trying though.

Andrey



"Dale Parfitt" wrote in message
news:mIs_c.2344$vI2.712@trnddc02...

"Bill Turner" wrote in message
...
On Sat, 4 Sep 2004 14:57:09 -0700, "Andrey"
wrote:

Greetings to all the antenna experts here!
I want to create horizontally polarized antenna, low profile, located
above
large ground plane. And I need it to be omnidirectional (sort of) and
have
sufficient gain in horizontal plane.
My frequency of interest is 900 MHz. The ground plane is a roof of a
car.
I tried loops, from 50 to 300 mm diameter, radiation goes up if I mount
it
above the ground plane.
Any ideas?
Thank you,
Andrey

__________________________________________________ _______

FWIW, horizontal polarization at 900 MHz won't get you far. Vertical is
preferred because horizontal is rapidly absorbed by ground loss. On the
other hand, if you don't *want* to get very far, use a vertical and just
reduce power.
This will be sad news to all the V/U weak signal ops who have
consistantly
covered long distances using horizontal polarity.

Dale W4OP

Andrey wrote:
Greetings to all the antenna experts here!

I want to create horizontally polarized antenna, low profile, located above
large ground plane. And I need it to be omnidirectional (sort of) and have
sufficient gain in horizontal plane.

My frequency of interest is 900 MHz. The ground plane is a roof of a car.

I tried loops, from 50 to 300 mm diameter, radiation goes up if I mount it
above the ground plane.

Any ideas?

Thank you,

Andrey


Good Morning Andrey,

What you are proposing is not an easy task any horizontal antenna placed
close to a good ground plain is going to have most of it's signal at
90 degrees. ( Straight up) Until the antenna is at least 1/2 wave above
the ground plan. at that point it will start to show radiation to the
horizon. EZNEC shows max gain at 30 degrees to the horizon for a 1/2
wave horizontal dipole mounted 1/2 wave above perfect ground and the
pattern looks somewhat like a peanut shape. if you move the antenna up
to 1 fullwave length above the ground plain then the patern does not
change much but the elevation angle dose you then get a good lobe at 15
degrees and another at 45 degrees. hope this is of some help.
Dave kc1di

Thank you Dave,

for sharing with me results of your simulation. I got similar results. The
thing that works is slit pipe (Alford's slot, see
http://www.eta.chalmers.se/~pgp/alfo...lford_eng.html for example)

Pipe works over ground plane as well (not as well, beam gets lifted, stll
there is enough energy looking on the horizon). It is such a cumbersome
thing though - looks funny on car's roof. Not of ractical use.

And I still can not find anything else that does it.


Regards,

Andrey Gleener


"KC1DI" wrote in message
...
Andrey wrote:
Greetings to all the antenna experts here!

I want to create horizontally polarized antenna, low profile, located
above
large ground plane. And I need it to be omnidirectional (sort of) and
have
sufficient gain in horizontal plane.

My frequency of interest is 900 MHz. The ground plane is a roof of a
car.

I tried loops, from 50 to 300 mm diameter, radiation goes up if I mount
it
above the ground plane.

Any ideas?

Thank you,

Andrey


Good Morning Andrey,

What you are proposing is not an easy task any horizontal antenna placed
close to a good ground plain is going to have most of it's signal at
90 degrees. ( Straight up) Until the antenna is at least 1/2 wave above
the ground plan. at that point it will start to show radiation to the
horizon. EZNEC shows max gain at 30 degrees to the horizon for a 1/2
wave horizontal dipole mounted 1/2 wave above perfect ground and the
pattern looks somewhat like a peanut shape. if you move the antenna up
to 1 fullwave length above the ground plain then the patern does not
change much but the elevation angle dose you then get a good lobe at 15
degrees and another at 45 degrees. hope this is of some help.
Dave kc1di

"Bill Turner" wrote in message
...
On Sun, 05 Sep 2004 00:02:26 GMT, "Dale Parfitt"
wrote:

This will be sad news to all the V/U weak signal ops who have
consistantly
covered long distances using horizontal polarity.

__________________________________________________ _______

This fellow was planning to put his antenna on the roof of a car.
Presumably he is *not* DXing.

I was therefore speaking of groundwave coverage, not any kind of skip,
and what I stated holds true; for local groundwave, vertical is best.

DXers, on the other hand, use horizontal precisely because the local
groundwave coverage is poor, thereby reducing local QRM but having
little or no effect on skip signals.

--
Bill, W6WRT
QSLs via LoTW


I wasn't talking about skip either- the majority of V/U weak signal work is
extended ground wave via perhaps enhanced tropo.

1.Horizontal polarity can take advantage of ground gain reflection that
vertical polarity cannot.

2. In addition, at 900 MHz where a wavelength is just over a foot, even
mounting the antenna at 12" would place the first lobe at 15 degrees,
assuming the car roof completely determines this- and I doubt that it has
much of an effect on far field take off angle.

Dale W4OP

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. The attenuation of ground waves increases with
frequency, to the point that they're virtually useless at VHF and above.
So at those frequencies, I'd think the polarization choice for short
range communication would be based on how it affects attenuation,
multipath, and QRM. Given those criteria, horizontal might well have an
advantage for short range communication, in some locations at least. And
it's long been favored for long range VHF/UHF communication.

Roy Lewallen, W7EL

Bill Turner wrote:
On Sun, 05 Sep 2004 00:02:26 GMT, "Dale Parfitt"
wrote:


This will be sad news to all the V/U weak signal ops who have consistantly
covered long distances using horizontal polarity.


__________________________________________________ _______

This fellow was planning to put his antenna on the roof of a car.
Presumably he is *not* DXing.

I was therefore speaking of groundwave coverage, not any kind of skip,
and what I stated holds true; for local groundwave, vertical is best.

DXers, on the other hand, use horizontal precisely because the local
groundwave coverage is poor, thereby reducing local QRM but having
little or no effect on skip signals.

--
Bill, W6WRT
QSLs via LoTW

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?

1.Horizontal polarity can take advantage of ground gain reflection that
vertical polarity cannot.

2. In addition, at 900 MHz where a wavelength is just over a foot, even
mounting the antenna at 12" would place the first lobe at 15 degrees,
assuming the car roof completely determines this- and I doubt that it has
much of an effect on far field take off angle.

You'd get that 15 degree lobe only if the roof extends far enough from
the antenna to reflect a wave going out at an angle 15 degrees below the
horizon (plus a bit, because the reflection doesn't actually take place
from a single point). At 12" above the car roof, the 15 degree downward
wave strikes the roof 12/tan(15 deg.) ~ 45 inches from the point below
the antenna. So the the car roof would have to extend at least about 4
feet beyond the antenna in the direction you're sending in order to get
that 15 degree lobe with the antenna 12" above the roof.

Roy Lewallen, W7EL

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

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.


--
73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB)
Editor, 'The VHF/UHF DX Book'
http://www.ifwtech.co.uk/g3sek