24 Apr
2014
24 Apr
'14
11:22 a.m.
------------------------------
Message: 3
Date: Thu, 24 Apr 2014 13:50:50 +0200
From: Juan Antonio Fernandez <ea4cyq(a)gmail.com>
Subject: [Moon-Net] Stacking distance 4x9 DK7ZB
To: moon-net <moon-net(a)mailman.pe1itr.com>
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Hello all!
I have purchased these antennas built by WIMO as WY209 reference.
The WIMO Manual tells that:
Vertical distance: 3.40m
Horizontal distance: 3.22m
It is strange that vertical distance is longer than horizontal distance. I
asked WIMO about it and they told me that this info is from DK7ZB source.
I can`t find original DK7ZB info, but in the VE7BQH chart shows a DK7ZB 9
elements a bit sorter ( 2.39wl in spite of 2.5wl from WIMO), where the
distances are:
Vertical distance: 3.32m
Horizontal distance: 3.56m
Could someone clarifies what could be the best stacking distance for these
4x9 elements antenna.
Thank you very much in advance.
Juan Antonio
EA4CYQ
24 Apr
24 Apr
11:53 a.m.
Indeed Ivan
The latest antenna designs are more dedicated to reduce side lobes and get
what they call low noise.
Obviously this is achieved by sacrificing some gain.
In the end, the GT will be the same.
Despite this is all pure theory, it´s a good fun, and keeps the operator in
peace with him self, if, at least, in theory the antenna is correct
assembled.
You can allays have good fun modeling the stack on EZnec, then generate the
FF-Tab and run it on TANT to see the GT value
73
2014-04-24 16:22 GMT+01:00 Ivan Kaitmann <ivaknn(a)gmail.com>om>:
------------------------------
Message: 3
Date: Thu, 24 Apr 2014 13:50:50 +0200
From: Juan Antonio Fernandez <ea4cyq(a)gmail.com>
Subject: [Moon-Net] Stacking distance 4x9 DK7ZB
To: moon-net <moon-net(a)mailman.pe1itr.com>
Message-ID:
<CA+5nehNKRinAwSxC8phmF0s=Pn=W=Yn9BYP9TJD95=M5+us9bQ(a)mail.gmail.com>
Content-Type: text/plain; charset="utf-8"
Hello all!
I have purchased these antennas built by WIMO as WY209 reference.
The WIMO Manual tells that:
Vertical distance: 3.40m
Horizontal distance: 3.22m
It is strange that vertical distance is longer than horizontal distance. I
asked WIMO about it and they told me that this info is from DK7ZB source.
I can`t find original DK7ZB info, but in the VE7BQH chart shows a DK7ZB 9
elements a bit sorter ( 2.39wl in spite of 2.5wl from WIMO), where the
distances are:
Vertical distance: 3.32m
Horizontal distance: 3.56m
Could someone clarifies what could be the best stacking distance for these
4x9 elements antenna.
Thank you very much in advance.
Juan Antonio
EA4CYQ
25 Apr
25 Apr
9:50 p.m.
On 24 Apr 2014 16:53, "Antonio Matias" <ct1ffu(a)gmail.com> wrote:
Indeed Ivan
The latest antenna designs are more dedicated to reduce side lobes and
get what
they call low noise.
Obviously this is achieved by sacrificing some gain.
Why is this obviously so?
I believe in practice it tends to be so, but it is not clear to me it
should obviously be so. In fact, logic tells me that power radiated in
sidelobes leaves less in the forward direction so reduces gain.
29 Apr
29 Apr
9:22 p.m.
Hi David,
I can not give a stringent proof, but to me it is obvious.
Some examples:
Maximum gain from a circular aperture is obtained when the
amplitude and phase are the same over the entire aperture.
(think telescope with lenses) The radiation pattern is then
a Bessel function and it has sidelobes. To reduce them one
would have to make the amplitude fall off gradually towards
the edges and obviously maximum gain is no longer obtained.
When you stack yagi antennas, maximum gain is obtained when
the side lobes are about -9 dB only.
If you model a yagi antenna as a structure with a somewhat
reduced wave speed (90 degrees phase shift from end to end
vs free space) you get a pattern wit sidelobes similar to
those of a circular aperture. That is the maximum gain for
the length of the structure. You can increase the wave speed
(go to a lower frequency) Then the gain is lower and the
sidelobes weaker.
The mathematics is similar to the design of filters.
If you want to design a low pass filter you can make it steeper
by forcing a zero at some point above the corner frequency.
The zero will obviously be followed by a non-zero at a somewhat
higher ferquency...
73
Leif / SM5BSZ
On 24 Apr 2014 16:53, "Antonio Matias"
<ct1ffu(a)gmail.com> wrote:
Indeed Ivan
The latest antenna designs are more dedicated to reduce side lobes and
get what
they call low noise.
Obviously this is achieved by sacrificing some
gain.
Why is this obviously so?
I believe in practice it tends to be so, but it is not clear to me it
should obviously be so. In fact, logic tells me that power radiated in
sidelobes leaves less in the forward direction so reduces gain. 
11:49 p.m.
Hi David.
I was hoping someone else would answer first and make the logical argument.
Leif's explanation makes sense.
Anyone that has done much antenna modeling has practical knowledge of these
trade-offs. A yagi is not perfect so it is simply not practical to produce
a single lobe antenna. There are several trade-offs that can be made. Quite
often gain is maximized without a lot of attention to other factors. Often
when a little gain is sacrificed other good factors can be improved on like
side-lobes. The factors that can be traded are gain, side-lobes, impedance
(real low is not practical),SWR bandwidth, and design frequency ( Best to
design a bit high in frequency because rain and other yagis in a stack
reduce the tuning frequency). A yagi designed for absolute maximum gain
would not be a practical design. Usually it would have high side-lobes,
very low impedance (perhaps 2 ohms), very narrow SWR bandwidth and would be
a narrow design that is easily detuned by rain. In all likely-hood the gain
would not be realized due to inefficiencies in the elements and the
matching network trying to work into a 2 ohm load. The model would likely
to be in error as well. Many of us have seen a yagi with gain that is 10 or
20 db too high and shows a 6db front to back ratio. These are not real
designs and show flaws in the modeling.
There is an optimum number of elements per boom length depending on design
objectives. There are also optimum boom lengths where front to back and
maximum gain converge better. A yagi designed for absolute minimum
side-lobes will tend to sacrifice 1 to 2 db of gain. It is possible to
reduce side-lobes significantly when only .5db of gain is sacrificed. This
is practical when you have plenty of power and have a high noise level.
73, Jim Shaffer, WB9UWA.
On Tue, Apr 29, 2014 at 8:22 PM, Leif Asbrink <leif(a)sm5bsz.com> wrote:
Hi David,
I can not give a stringent proof, but to me it is obvious.
Some examples:
Maximum gain from a circular aperture is obtained when the
amplitude and phase are the same over the entire aperture.
(think telescope with lenses) The radiation pattern is then
a Bessel function and it has sidelobes. To reduce them one
would have to make the amplitude fall off gradually towards
the edges and obviously maximum gain is no longer obtained.
When you stack yagi antennas, maximum gain is obtained when
the side lobes are about -9 dB only.
If you model a yagi antenna as a structure with a somewhat
reduced wave speed (90 degrees phase shift from end to end
vs free space) you get a pattern wit sidelobes similar to
those of a circular aperture. That is the maximum gain for
the length of the structure. You can increase the wave speed
(go to a lower frequency) Then the gain is lower and the
sidelobes weaker.
The mathematics is similar to the design of filters.
If you want to design a low pass filter you can make it steeper
by forcing a zero at some point above the corner frequency.
The zero will obviously be followed by a non-zero at a somewhat
higher ferquency...
73
Leif / SM5BSZ
--
Earl Shaffer, WB9UWA
My EME array photos
http://www.gm4jjj.co.uk/WB9UWA/array_files/page33-1001-full.html
Detailed array photos
http://www.gm4jjj.co.uk/WB9UWA/
Facebook
http://www.facebook.com/earl.shaffer
Linkedin
http://www.linkedin.com/pub/earl-shaffer/12/881/735
On 24 Apr 2014 16:53, "Antonio Matias"
<ct1ffu(a)gmail.com> wrote:
_______________________________________________
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Indeed Ivan
The latest antenna designs are more dedicated to reduce side lobes and
get what
they call low noise.
Obviously this is achieved by sacrificing some
gain.
Why is this obviously so?
I believe in practice it tends to be so, but it is not clear to me it
should obviously be so. In fact, logic tells me that power radiated in
sidelobes leaves less in the forward direction so reduces gain.
3321
days inactive
3327
days old
4 comments
5 participants
participants (5)
-
Antonio Matias -
Dr. David Kirkby -
Earl Shaffer -
Ivan Kaitmann -
Leif Asbrink