I say ignore the TOA. (For those unfamiliar with the term, it's the
"takeoff angle", which usually means the elevation angle at which the
antenna pattern is strongest.)

What counts is the gain at the elevation angle at which you want to
communicate. This, in turn, depends on the distance and the propagation
conditions. If you need a strong signal at an elevation angle of 15
degrees, it doesn't matter whether the TOA is 10 degrees, 15, or 20 or
zero. All that counts is the gain at 15 degrees. And an antenna with TOA
of 15 degrees doesn't necessarily have the most gain at 15 degrees of
any antenna.

Consider the following three 40 meter antennas: A vertical antenna with
about 8 radials (18 ohm ground system resistance), a dipole at 30 feet,
and a dipole at 40 feet, all over average ground.

Antenna TOA deg Gain at 26 deg. Gain at 15 deg.

Vert 26 -1.76 dBi -2.72 dBi
Dipole @ 30' 90 (straight up) 2.58 dBi -1.28 dBi
Dipole @ 40' 51 3.9 dBi 0.32 dBi

-- Which one has the lowest takeoff angle?
-- Which one is the best for communicating at 26 deg. elevation angle?
-- Which one is the best for communciating at 15 deg. elevation angle?

What does the takeoff angle have to do with which antenna is best?

Roy Lewallen, W7EL

art wrote:
Most people have added an amplifier only to find out that the
difference in signal
was very small. Thus many people deride the value of a 'silly' db gain
whereas DX'ers say that a single db extra is a lot !
Fact is that most long distance signals on 20 metres come in at angles
of 11 degrees or less where as the 'normal' antenna has a TOA of around
14 degrees.
So where a dxer points to the extra 1db gain as being everything in
fact it is the lowering of the TOA that comes with the extra gain. In
my opinion if one designs his antenna for a lower TOA say 10 to 11
degrees then even tho its gain may well be below the dxers choise( a
very long boom or stacked antennas) the lower TOA with less gain will
show little difference
to the antenna of choics because the lower edge of the radiation lobe
will follow the same line and any extra gain provided will have the
same effect of adding an amplifier which is minimal compared to the
ability of capturing signals that arrive at low angles.
I believe it is time for antenna designers to concentrate less on
obtaining gain and instead concentrate more on lowering the TOA.
without the need of excessive real estate requirements.
What say ?
Art

On Fri, 28 Jan 2005 21:28:20 -0800, Roy Lewallen
wrote:

What does the takeoff angle have to do with which antenna is best?


That would depend on the desired contact. If you want 80 meters DX,
you want a very high antenna, if you just want to talk to your local
buddies, a lower antenna provides a better NVIS.

Verticals provide better omni-directional pattern but a slanted dipole
provides better directivity than a vertical.

Beams are obvious.


--
Buck
N4PGW

*Sigh*

I tried.

Roy Lewallen, W7EL

Buck wrote:
On Fri, 28 Jan 2005 21:28:20 -0800, Roy Lewallen
wrote:


What does the takeoff angle have to do with which antenna is best?



That would depend on the desired contact. If you want 80 meters DX,
you want a very high antenna, if you just want to talk to your local
buddies, a lower antenna provides a better NVIS.

Verticals provide better omni-directional pattern but a slanted dipole
provides better directivity than a vertical.

Beams are obvious.

Roy Lewallen wrote:

*Sigh*

I tried.



Let me have a shot at it, Roy.

possible blather alert!

Perhaps there is confusion by some people with the idea that the
takeoff angle. I suspect that a lot of people think of their RF leaving
the antenna as a "blob" that leaps out at some desired or undesired angle.

Instead, the RF is heading off in all directions, with some angles
having more relative power.

So even if an antenna has a lower TOA, it might be less gain than an
antenna that has a higher TOA has at that angle.

An inefficient antenna with a low TOA can be less efficient at that low
TOA than a more efficient antenna with a higher TOA is at that same low TOA.

Oy.

- Mike KB3EIA -

rest snipped

Mike Coslo wrote:
Perhaps there is confusion by some people with the idea that the
takeoff angle. I suspect that a lot of people think of their RF leaving
the antenna as a "blob" that leaps out at some desired or undesired angle.

Instead, the RF is heading off in all directions, with some angles
having more relative power.

So even if an antenna has a lower TOA, it might be less gain than an
antenna that has a higher TOA has at that angle.

An inefficient antenna with a low TOA can be less efficient at that
low TOA than a more efficient antenna with a higher TOA is at that same
low TOA.

Maybe a picture is worth a thousand words. Here's a comparison
radiation pattern for my 130 ft dipole Vs my 40m vertical with
elevated radials. In the dipole's favored direction, it's TOA
is greater than the vertical's yet the dipole radiates more
power than the vertical even at the vertical's TOA. Here's the
pictu http://www.qsl.net/w5dxp/dipvsver.htm
--
73, Cecil, W5DXP


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Thanks, Cecil.

Roy Lewallen, W7EL

Cecil Moore wrote:

Maybe a picture is worth a thousand words. Here's a comparison
radiation pattern for my 130 ft dipole Vs my 40m vertical with
elevated radials. In the dipole's favored direction, it's TOA
is greater than the vertical's yet the dipole radiates more
power than the vertical even at the vertical's TOA. Here's the
pictu http://www.qsl.net/w5dxp/dipvsver.htm
--
73, Cecil, W5DXP

On Sat, 29 Jan 2005 07:54:16 -0600, Cecil Moore
wrote:

Maybe a picture is worth a thousand words. Here's a comparison
radiation pattern for my 130 ft dipole Vs my 40m vertical with
elevated radials. In the dipole's favored direction, it's TOA
is greater than the vertical's yet the dipole radiates more
power than the vertical even at the vertical's TOA. Here's the
pictu http://www.qsl.net/w5dxp/dipvsver.htm

Exactly!

Thing is....So did my model when using "medium" ground quality.
But I know in the real world, my vertical smoked the dipole on long
haul/low angles. I'm almost positive that the verticals are
"underpowered" when
modeling, unless you bump up the ground quality. Or at least when used
on the low bands at night. To make the model of my dipole vs vertical
actually pan out as in real life, I had to bump up the ground quality
to
"excellent". Even then, it might have been a bit lower than real life.
I'm not sure what to make if this....
I'm not the only one to notice this also.... Talk to W8JI about his
nearly
300 ft dipole vs his verticals on 160m...He always thought the dipole
would be
better. After all, modeling says it should be. But it didn't quite pan
out...
I basically ignore Cecils bad experience, because #1, his vertical
needed more radials,
and he never used it for long haul paths. So of course, the vertical
should
have lost in his case. Heck, even with my vertical, that was a bit
better than his,
I had to get over 1000 miles to start seeing the vertical overtake the
dipole.
Those dipole vs vertical modeling plots are *very* misleading. Or to me
anyway...
Myself, I think the ground qualities applied are in error for some
reason..
They overly stunt the vertical when modeling...Either that, or my
ground here is
really good...My ground quality is pretty good, but it's not *great*,
being I'm
in the city cement jungle of Houston. MK

Yes, you've got it. Hopefully some of the folks who didn't understand my
explanation will understand yours.

Roy Lewallen, W7EL

Mike Coslo wrote:

Let me have a shot at it, Roy.

possible blather alert!

Perhaps there is confusion by some people with the idea that the
takeoff angle. I suspect that a lot of people think of their RF leaving
the antenna as a "blob" that leaps out at some desired or undesired angle.

Instead, the RF is heading off in all directions, with some angles
having more relative power.

So even if an antenna has a lower TOA, it might be less gain than an
antenna that has a higher TOA has at that angle.

An inefficient antenna with a low TOA can be less efficient at that
low TOA than a more efficient antenna with a higher TOA is at that same
low TOA.

Oy.

- Mike KB3EIA -

rest snipped

On Fri, 28 Jan 2005 23:25:19 -0800, Roy Lewallen
wrote:

*Sigh*

I tried.

You can lead a horse to water.....


Roy Lewallen, W7EL

Buck wrote:
On Fri, 28 Jan 2005 21:28:20 -0800, Roy Lewallen
wrote:


What does the takeoff angle have to do with which antenna is best?



That would depend on the desired contact. If you want 80 meters DX,
you want a very high antenna, if you just want to talk to your local
buddies, a lower antenna provides a better NVIS.

Verticals provide better omni-directional pattern but a slanted dipole
provides better directivity than a vertical.

Beams are obvious.