It is more a question of practicality.
It is being done by those with crankup towers, if they want to optimize, say
between DXing at low angles and domestic QSOs at higher angles. If you want
to be flexible, get crankup tower and StepIR antenna.

What you suggesting is asking for mechanical complexity, guy wires, multiple
antennas on the same tower in the way, etc.

Propagation is not clear cut X angle. It is more like drunken, wobbly
signals varying in angles, polarization and direction. Antennas have quite a
wide lobes to accommodate most of that. Serious DXers and contesters use
stacks that give them instantaneous selection of major angles.

Tilting up antenna about 5 deg. helps somewhat, beyond that it doesn't.
Vertical angle of beam is given by the height of the antenna.

So it the question of practicality vs. "precision" and complexity. Moving it
10 ft up or down doesn't really buy you anything.

73 Yuri, K3BU

"CW" wrote in message
oups.com...
Dave,

Thanks for the reply. Multiple switched Yagi's at various heights is a
practical approach, and I'm delighted to hear that "sometimes there is
a lot of difference". What you are describing is a coarse grained
approach to the problem, which is also commonly done in the horizontal
plane by switching vertical antenna arrays, etc.
A fellow ham in the area has a Yagi mounted about half way up his guyed
tower, on a swing arm. It can rotate, but is limited to about 300
degrees of rotation. A similar setup could be used on a side mounted
tower trolly, where the height could be continuously varied by 30 feet
or more, AND rotated through about 300 degrees.
73,
CW-AI4MI



its really only practical on crank up type towers, for those with guyed
towers its usually not possible.

10' change on 20m would likely not be very useful though. my hf stacks
for
10/15/20 are all spaced 30' apart, 40m is spaced about 80'. even with
those
height changes (which i can select instantly so i can make direct
comparisons without worrying about fading) there is often little
difference
between antennas... though sometims there is a lot of difference. This
highlights the fact that often the signals arrive with a wide range of
angles, though at some times they must be in a relatively narrow range.
so
having multiple antennas at different heights that can be selected in
various combinations is a handy thing to do.

That actually changes it a lot less than raising and lowering
significantly. HF yagis a wavelength or two above ground don't have
laser-like beams. The elevation pattern is set up substantially by
ground reflection, not only the antenna's free-space elevation pattern.

Check out

http://n3ox.net/pictures/20m_yagi_el.jpg

for an illustration of what happens when you tilt a 5 element 20m yagi
up toward the sky. I don't remember how high it is; I think it's about
1 wavelength high. The traces are for 0, 20, 40 and 60 degrees
inclination.

73,
Dan

Cecil
That makes a lot of sense after all if one has the antenna primed for
low angles then propagation will render it useless as time goes by for
those particular angles. If by tipping or feeding another element in an
array you can move or thicken the main lobe you can increase the gain
of a signal by more than 2 S units then it is certainly worthwhile.To
view the subject purely around the maximum gain angle of the main lobe
is fallacious as it is the signal that falls just outside the main lobe
contour that may be the most desirable and subject to the largest
possible gain with the smallest change of TOA. This is because the main
lobe thickens out to cover the deep crevice of non coverage of an array
tuned for a low TOA.and allows you to emulate the performance of a
stacked array with the use of the lower beam alone. 2S unit increase of
a signal that can be barely heard is much more advantageous than
increasing the gain of a signal that is blowing away all other nearby
signals, it certainly allows for more communication data to be
transferred where initially very little could be heard.
If a good contact is underway it is certainly desirable to maintain
that contact even tho propagation is changing and that is what the
original poster is seeking
Art

Cecil Moore wrote:
CW wrote:
I've been wondering for some time now why amateur operators don't build
their Yagi antenna's
so they can be raised and lowered about 10ft in addition to being
rotated.

Many do, using motor driven towers. In addition to lowering
their arrays when a storm hits, some raise and lower their
towers during marginal conditions to maximize signal strength.
--
73, Cecil http://www.w5dxp.com

ORIGINAL MESSAGE:

On 15 Oct 2006 09:26:05 -0700, "art" wrote:


If by tipping or feeding another element in an
array you can move or thicken the main lobe you can increase the gain
of a signal by more than 2 S units then it is certainly worthwhile.

------------ REPLY FOLLOWS ------------

Not necessarily worthwhile. Remember, if your antenna is optimized for
low-angle weak DX signals, the high-angle signals are going to be much
closer in and therefore much stronger to begin with. If you lose a few
dB on a S-9 signal, it won't matter.

If this was really a good idea, everybody would already be doing it.
As I mentioned before, it might be desirable for someone running QRP
or micropower, but not for most of us at the 100 watt or greater
level. Spend your money on other things.

Bill, W6WRT

Bill Turner wrote:
ORIGINAL MESSAGE:

On 15 Oct 2006 09:26:05 -0700, "art" wrote:


If by tipping or feeding another element in an
array you can move or thicken the main lobe you can increase the gain
of a signal by more than 2 S units then it is certainly worthwhile.

------------ REPLY FOLLOWS ------------

Not necessarily worthwhile. Remember, if your antenna is optimized for
low-angle weak DX signals, the high-angle signals are going to be much
closer in and therefore much stronger to begin with. If you lose a few
dB on a S-9 signal, it won't matter.

If a incoming signal aligns with the null between lobes then the
receiving station is deaf to your signal. Moving the lobe slightly
upwards can add a few db as you call it and allow for communication. If
you yell at a closed door you do not increase communication, whisper
under the door and you can then be heard, Its all relative. As far as
those that follow lemmings do it all the time.
Art

David, are you saying that your three-some stack is made out of tri
banders of the same design such that a lobe null can be filled? I
believe that is exactly the coverage the poster is looking for, he
wants to be around to hear when the tree falls
Art

Dave wrote:
"Cecil Moore" wrote in message
t...
CW wrote:
I've been wondering for some time now why amateur operators don't build
their Yagi antenna's
so they can be raised and lowered about 10ft in addition to being
rotated.

Many do, using motor driven towers. In addition to lowering
their arrays when a storm hits, some raise and lower their
towers during marginal conditions to maximize signal strength.
--

its really only practical on crank up type towers, for those with guyed
towers its usually not possible.

10' change on 20m would likely not be very useful though. my hf stacks for
10/15/20 are all spaced 30' apart, 40m is spaced about 80'. even with those
height changes (which i can select instantly so i can make direct
comparisons without worrying about fading) there is often little difference
between antennas... though sometims there is a lot of difference. This
highlights the fact that often the signals arrive with a wide range of
angles, though at some times they must be in a relatively narrow range. so
having multiple antennas at different heights that can be selected in
various combinations is a handy thing to do.

my stacks are all monobanders.
on 40m its 4-ele's at 180' & 100'
on 20m i have 4-ele's at 150/120/90/60'
on 15m and 10m its 4-ele's at 120/90/60/30'
on 20m, 15m, and 10m there is another 4 ele fixed south.
also on 20m, 15m, and 10m, the middle 2 are fixed at europe and selected
together, and the bottom ones are on ring rotors and separately rotatable
from the top one.

so on 20m, 15m, and 10m, i can select the top along, the middle two at
europe together, the bottom one alone, or the south one alone. And then i
can also select the top, middle, and bottom all together, and the top,
south, and bottom all together to spread the signal out when the bands are
open in more than one direction.


"art" wrote in message
oups.com...
David, are you saying that your three-some stack is made out of tri
banders of the same design such that a lobe null can be filled? I
believe that is exactly the coverage the poster is looking for, he
wants to be around to hear when the tree falls
Art

Dave wrote:
"Cecil Moore" wrote in message
t...
CW wrote:
I've been wondering for some time now why amateur operators don't
build
their Yagi antenna's
so they can be raised and lowered about 10ft in addition to being
rotated.

Many do, using motor driven towers. In addition to lowering
their arrays when a storm hits, some raise and lower their
towers during marginal conditions to maximize signal strength.
--

its really only practical on crank up type towers, for those with guyed
towers its usually not possible.

10' change on 20m would likely not be very useful though. my hf stacks
for
10/15/20 are all spaced 30' apart, 40m is spaced about 80'. even with
those
height changes (which i can select instantly so i can make direct
comparisons without worrying about fading) there is often little
difference
between antennas... though sometims there is a lot of difference. This
highlights the fact that often the signals arrive with a wide range of
angles, though at some times they must be in a relatively narrow range.
so
having multiple antennas at different heights that can be selected in
various combinations is a handy thing to do.

On 14 Oct 2006 22:59:10 -0700, "
wrote:

That actually changes it a lot less than raising and lowering
significantly. HF yagis a wavelength or two above ground don't have
laser-like beams. The elevation pattern is set up substantially by
ground reflection, not only the antenna's free-space elevation pattern.

Gotcha. That makes sense.

Thanks, Tony

Now now Tony, be carefull in what you say and how you say it

If you placed several dipoles above each other in an array, say nine of
them within a height change of half a wave length, in line and each of
the dipoles/elements were resonant at the same frequency you are then
infering ......,at least I think you are,....... that the lowest
dipole/element will have the highest TOA, the next element in height
will have a lower TOA and progressively until one energises the top
element to get the lowest TOA of them all............ If that is what
you are saying........... then you could not be more wrong.
I am sure that those who are really knoweledgable in the field will
agree with me.
Ofcourse somebody lacking true knoweledge will produce a fake series of
radiation patterns for each element in the array but that is par for
the course on this newsgroup.
But then again often interpretations can be varied and thus in error if
so I apologise.
Best Regards
Art







Tony VE6MVP wrote:
On 14 Oct 2006 22:59:10 -0700, "
wrote:

That actually changes it a lot less than raising and lowering
significantly. HF yagis a wavelength or two above ground don't have
laser-like beams. The elevation pattern is set up substantially by
ground reflection, not only the antenna's free-space elevation pattern.

Gotcha. That makes sense.

Thanks, Tony

"CW" wrote in message
ups.com...
Fellows,

I've been wondering for some time now why amateur operators don't build
their Yagi antenna's
so they can be raised and lowered about 10ft in addition to being
rotated.
It seems to me that raising and lowering the height of a Yagi affects
the take-off angle by at least several degrees, meaning that the signal
delivery (target area) would be moved by at least many hundreds of
miles.

I don't know if this helps, but advice for TV DX says that you get
progressively improved performance until the yagi's
height-above-average-terrain (HAAT) is equal to about ten wavelengths.
(Above that HAAT, the signal strength varies up and down with further
increases in the elevation )

I never tested the idea, but if correct and it also holds for HF, there
won't ever be anybody _lowering_ a HF yagi. We would want the most height.
At the 2006 Field Day, one team had multi-band beam at 85 feet and everybody
loved it.

Before anybody tells me there is a difference between a yagi and a beam, let
me thank you in advance. I cannot formulate a sensible distinction
between them and I welcome the knowledge. I presume the terms are related
but not interchangeable.

73