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Vertical Yagi?



 
 
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  #11  
Old July 13th 08, 01:53 PM posted to rec.radio.amateur.antenna
Alan Peake[_2_]
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Posts: 28
Default Vertical Yagi?



Roy Lewallen wrote:
One of the advantages of a Yagi is its directivity. When mounted
horizontally, its horizontal pattern is quite directional, but the
pattern in the vertical plane is relatively broad -- the vertical
pattern of a typical HF Yagi in the forward direction, in fact, isn't
much different from a single dipole. If you mount the Yagi vertically,
the two patterns swap so the horizontal pattern ends up very much
broader than when mounted vertically.


Roy, are you talking about high gain yagis? I just looked at the
beamwidths of an 11 element DL6WU Yagi on 2m and got 35 degrees
horizontal and 39 degrees vertical in EZNEC. Not much difference there.
Alan

  #12  
Old July 13th 08, 03:03 PM posted to rec.radio.amateur.antenna
John Ferrell
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Posts: 199
Default Vertical Yagi?

On Sun, 13 Jul 2008 12:38:20 GMT, "Dave" wrote:

http://www.nn4zz.com/tiltplate.htm

That looks like it is real close to what I need!
Thanks!
John Ferrell W8CCW


"Dave" wrote in message news:HEbek.91$kf4.54@trnddc03...

"John Ferrell" wrote in message
...
Why do we always mount our HF Yagi's in the horizontal plane?
Antenna maintenance would be much easier for those of us with tilt
over towers if the antenna were in the horizontal plane when down for
maintenance!

John Ferrell W8CCW


vertical yagi's work fine... if you can get them far enough away from the
conductive tower and mast either vertically or horizontally... though i do
believe you get better ground reflection from the horizontal polarization.
There is a new product that allows yagis mounted horizontally to
automatically pivot as you tilt over a tower so they stay level with the
ground.


  #13  
Old July 13th 08, 03:09 PM posted to rec.radio.amateur.antenna
John Ferrell
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Posts: 199
Default Vertical Yagi?

The EZNEC5 model that I did left me with the feeling that my model was
too vague.
John Ferrell W8CCW

On Sun, 13 Jul 2008 00:59:30 -0700, Roy Lewallen
wrote:

One of the advantages of a Yagi is its directivity. When mounted
horizontally, its horizontal pattern is quite directional, but the
pattern in the vertical plane is relatively broad -- the vertical
pattern of a typical HF Yagi in the forward direction, in fact, isn't
much different from a single dipole. If you mount the Yagi vertically,
the two patterns swap so the horizontal pattern ends up very much
broader than when mounted vertically.

A vertically mounted Yagi is vertically polarized, and vertically
polarized radiation reacts differently with the ground than horizontally
polarized radiation. So rotating a moderately or very high yagi from
horizontal to vertical will result in loss of low angle radiation unless
your ground is very highly conductive.

These effects can be very easily be seen by modeling.

Roy Lewallen, W7EL

John Ferrell wrote:
Why do we always mount our HF Yagi's in the horizontal plane?
Antenna maintenance would be much easier for those of us with tilt
over towers if the antenna were in the horizontal plane when down for
maintenance!

John Ferrell W8CCW

  #14  
Old July 13th 08, 07:22 PM posted to rec.radio.amateur.antenna
Bryan
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Posts: 199
Default Vertical Yagi?

John Ferrell wrote:
Why do we always mount our HF Yagi's in the horizontal plane?
Antenna maintenance would be much easier for those of us with tilt
over towers if the antenna were in the horizontal plane when down for
maintenance!

John Ferrell W8CCW


Over the past 38 years, I've had HF yagis... a homebrew 3-el 15m monoband
yagi (16' boom) and 3-element triband trap yagis (12' booms) on tiltover
masts. I've never encountered maintenance issues with operating them in the
horizontal plane. A step lader is all that's needed to reach the driven
element, and the antenna can be rotated to reach both parasitic elements.

It seems to me that while Front/Back ratio might be similar, a vertically
polarized yagi would have a significantly reduced Front/Side ratio. If
operated in the vertical plane, I'm guessing that performance may also be
adversely affected by a conductive mast in the near-field. If performance
was same/similar and maintenance was much easier, I think you'd see many
more vertically polarized HF yagis.

Bryan WA7PRC


  #15  
Old July 13th 08, 09:28 PM posted to rec.radio.amateur.antenna
John Ferrell
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Posts: 199
Default Vertical Yagi?

On Sun, 13 Jul 2008 11:22:44 -0700, "Bryan"
wrote:

John Ferrell wrote:
Why do we always mount our HF Yagi's in the horizontal plane?
Antenna maintenance would be much easier for those of us with tilt
over towers if the antenna were in the horizontal plane when down for
maintenance!

John Ferrell W8CCW


Over the past 38 years, I've had HF yagis... a homebrew 3-el 15m monoband
yagi (16' boom) and 3-element triband trap yagis (12' booms) on tiltover
masts. I've never encountered maintenance issues with operating them in the
horizontal plane. A step lader is all that's needed to reach the driven
element, and the antenna can be rotated to reach both parasitic elements.

It seems to me that while Front/Back ratio might be similar, a vertically
polarized yagi would have a significantly reduced Front/Side ratio. If
operated in the vertical plane, I'm guessing that performance may also be
adversely affected by a conductive mast in the near-field. If performance
was same/similar and maintenance was much easier, I think you'd see many
more vertically polarized HF yagis.

Bryan WA7PRC

There have been several very credible posts that have convinced me
that I do need to stick with horizontal polarization with the Yagi.

Fortunately, the physical limitation of "no ladders" will go away in a
few months as I continue my recovery from two knee joint replacements.
However, as I get older I may find the limitation returning. I want to
be prepared for that time.

My antenna is modest in that it is only a Cushcraft A3S and I
generally keep the crank up antenna height at about 50 feet. This area
(Greensboro NC) does get an occasional hurricane and some ice storms.
There are times when I would like to reduce my risks on the forecast
weather.

I expect I will pursue a lighter (home brew) version of the Tilt Plate
system.

Currently the coax is fouled at the rotor and I will need outside
assistance to clear the problem. It is not a big issue but I do like
to solve my own problems!

John Ferrell W8CCW
  #16  
Old July 14th 08, 04:55 AM posted to rec.radio.amateur.antenna
Roy Lewallen
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Posts: 1,374
Default Vertical Yagi?

Alan Peake wrote:

Roy, are you talking about high gain yagis? I just looked at the
beamwidths of an 11 element DL6WU Yagi on 2m and got 35 degrees
horizontal and 39 degrees vertical in EZNEC. Not much difference there.
Alan


No, I'm not. The OP specified HF, so I'm talking about Yagis of up to 5
or 6 elements or so. Ones with a larger number of elements would
significantly narrow the pattern in both planes. I'm surprised that the
beamwidths approach about the same value, but I haven't done much
modeling or any measurement of Yagis with a large number of elements, so
I'll believe it.

Roy Lewallen, W7EL
  #17  
Old July 14th 08, 11:10 PM posted to rec.radio.amateur.antenna
Jim Lux
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Posts: 801
Default Vertical Yagi?

Alan Peake wrote:


Roy Lewallen wrote:
One of the advantages of a Yagi is its directivity. When mounted
horizontally, its horizontal pattern is quite directional, but the
pattern in the vertical plane is relatively broad -- the vertical
pattern of a typical HF Yagi in the forward direction, in fact, isn't
much different from a single dipole. If you mount the Yagi vertically,
the two patterns swap so the horizontal pattern ends up very much
broader than when mounted vertically.


Roy, are you talking about high gain yagis? I just looked at the
beamwidths of an 11 element DL6WU Yagi on 2m and got 35 degrees
horizontal and 39 degrees vertical in EZNEC. Not much difference there.
Alan



I think he's talking about lower gain (e.g. a 3 element beam for 20m),
where the 3dB beamwidth might be about 50-60 degrees in the Eplane
(parallel to the elements) and 80 degrees in the H plane (perpendicular
to the elements). The 80 is about the same as the 3dB beamwidth of a
dipole.

For higher gain antennas (e.g. your VHF/UHF), the beamwidths will be
pretty close in E and H planes. (since a larger fraction of the overall
antenna gain comes from "array pattern" gain rather than the individual
"element patterns")


Of course, the polarization sensitivity of the ground reflection makes
the horizontal antenna usually a winner overall.

  #18  
Old July 14th 08, 11:17 PM posted to rec.radio.amateur.antenna
Jim Lux
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Posts: 801
Default Vertical Yagi?

Roy Lewallen wrote:
Alan Peake wrote:

Roy, are you talking about high gain yagis? I just looked at the
beamwidths of an 11 element DL6WU Yagi on 2m and got 35 degrees
horizontal and 39 degrees vertical in EZNEC. Not much difference there.
Alan


No, I'm not. The OP specified HF, so I'm talking about Yagis of up to 5
or 6 elements or so. Ones with a larger number of elements would
significantly narrow the pattern in both planes. I'm surprised that the
beamwidths approach about the same value, but I haven't done much
modeling or any measurement of Yagis with a large number of elements, so
I'll believe it.



Here's a sort of intuitive approach to the conceptual analysis...


Consider the overall pattern to be like that of a phased array where you
multiply the pattern of an individual element by the pattern of the
array assuming that the elements were isotropic. Indeed, in a Yagi, not
all the elements are excited equally, but bear with me..

So, in a 3 element antenna with a gain of, say, 5dBi, you're getting
about 2 dBi of gain from just the dipoles, and 3dBi of gain from the
fact that you've got 3 elements in an array. The beamwidth is going to
be a combination of the array pattern (which is the same in vertical and
horizontal planes) and the element pattern (which is not)..


In a higher gain antenna (say 12dbi), you've got the same element gain
2dBi) but the array pattern gain is now 10dBi, so the shape of the
latter will dominate.



  #19  
Old July 22nd 08, 10:05 PM posted to rec.radio.amateur.antenna
John Ferrell
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Posts: 199
Default Vertical Yagi?

On Sat, 12 Jul 2008 15:46:27 -0400, John Ferrell
wrote:

Why do we always mount our HF Yagi's in the horizontal plane?
Antenna maintenance would be much easier for those of us with tilt
over towers if the antenna were in the horizontal plane when down for
maintenance!

John Ferrell W8CCW

I sometimes wonder if anybody ever does any actual work or if we just
talk about it here.

I offer up a progress report here with my work so far on the "Tilt
Over Gadget"

http://dixienc.us/TiltOverGadget/TiltOverGadget.mht

I will concede up front that it is but a crude prototype with some
unfinished aspects, but it works!

Thanks to all
John Ferrell W8CCW
  #20  
Old July 23rd 08, 03:06 AM posted to rec.radio.amateur.antenna
John Smith
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Posts: 2,915
Default Vertical Yagi?

John Ferrell wrote:

...
I offer up a progress report here with my work so far on the "Tilt
Over Gadget"

http://dixienc.us/TiltOverGadget/TiltOverGadget.mht

I will concede up front that it is but a crude prototype with some
unfinished aspects, but it works!

Thanks to all
John Ferrell W8CCW


Whatever that link is to, it will not open in internet explorer or
firefox on my computer ...

Regards,
JS
 




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