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.

David that is quite an array of antennas. Two questions come to mind.
Why the separation of a half versus 0.6 of a wave length?
and 2 do you ground the top antenna when it is not in use or let it
float?
I have heard that the top array can remove static noise to advantage
and I was wondering how that would compare to an elevated mast that
would provide a cone of protection and thus allow use of the top array
regardless of conditions.
Regards
Art

art wrote:
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.

that separation comes about from the spacing of guy wires on the rohn towers
they are on. it also happens to work out reasonably well with the elevation
pattern software since that many antennas fairly well covers the whole range
of take off angles from new england to most of the world.

all my yagis are completely grounded designs anyway, so there is no need to
further ground them when not in use. when there is rain or snow static the
top one often becomes too noisy to use while lower ones are just fine...
another good reason to rotate the bottom antennas (except on 40m where it
won't turn under the guy wires).



"art" wrote in message
ps.com...
David that is quite an array of antennas. Two questions come to mind.
Why the separation of a half versus 0.6 of a wave length?
and 2 do you ground the top antenna when it is not in use or let it
float?
I have heard that the top array can remove static noise to advantage
and I was wondering how that would compare to an elevated mast that
would provide a cone of protection and thus allow use of the top array
regardless of conditions.
Regards
Art

art wrote:
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.

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

ORIGINAL MESSAGE:

On 14 Oct 2006 06:32:21 -0700, "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.

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

The answer is because it isn't really necessary in most cases. If you
optimize your antenna for low-angle DX signals where you really need
the gain, there will still be significant radiation at high angles,
which are generally closer to you and will have stronger signals as a
result anyway.

This might be significant enough for a QRP operator to want to do it,
but at the 100 watt or higher level, you wouldn't gain much. Pun
intended. :-)

Bill, W6WRT

On 14 Oct 2006 06:32:21 -0700, "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.
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.

Or hows about raising and lowering the angle of the Yagi? Tilting it
somewhat? Maybe a winch and cable to the end of the Yagi and some
kind of rotatable joint at the tower end. That would also be complex
and cost some.

Tony

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

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