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I found iteresting replies about this subject and for this reason I am
sending a summary back to the reflector. Thank you all, it was vy
helpful!
Carlos - PY1CAS
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Date: Fri, 12 Sep 1997 03:46:25 -0700
From: Ed Sleight <k4sb@worldnet.att.net>
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Subject: Re: [TowerTalk] Dipole Height on the low bands
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Hi Carlos,,,,,well the answer to your high dipole on a building is what
does it see for ground....and I bet it sees all that steel flooring.
Might suggest you try installing it on the very edge of the building and
see what happens, but pick which side carefully...it's going to be very
directional toward the perpendicular of that wall.
73
Ed
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From: "bryan edwards" <bryan@prodistributors.com>
To: <py1cas@ax.apc.org>
Subject: Re: [TowerTalk] Dipole Height on the low bands
To: <towertalk@contesting.com>
Date: Fri, 12 Sep 1997 14:14:06 -0500
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The higher the better for long haul DX work.....
Bryan W5KFT
----------
> From: Carlos Augusto S. Pereira <py1cas@ax.apc.org>
> To: towertalk@contesting.com
> Subject: [TowerTalk] Dipole Height on the low bands
To: <towertalk@contesting.com>
> Date: Friday, September 12, 1997 2:44 PM
>
> Dear friends,
>
> We all know that the height of a dipole over the ground deeply
> influences the take-off angle of a horizontaly polarized antenna. With a
> higher antenna we should expect a lower radiation angle. Right?
>
> Well, we also know that for 80m we need at least 1/2 wavelenght in order
> to obtain a 30 degrees angle. For that we need a very high tower! But if
> we install a dipole for 80 meters on the top of a very tall building?
> What happens? Can we expect a low angle or not, or there are more
> parameters involved on it?
>
> Thanks in advance,
>
> Carlos - PY1CAS
> E-mail: py1cas@ax.apc.org
>
> --
> FAQ on WWW: http://www.contesting.com/towertalkfaq.html
> Submissions: towertalk@contesting.com
> Administrative requests: towertalk-REQUEST@contesting.com
> Problems: owner-towertalk@contesting.com
> Search: http://www.contesting.com/km9p/search
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From: Stu Greene <wa2moe@doitnow.com>
Subject: Re: [TowerTalk] Dipole Height on the low bands
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At 04:44 PM 9/12/97 -0300, you wrote:
But if
>we install a dipole for 80 meters on the top of a very tall building?
>What happens? Can we expect a low angle or not,
YES & 73
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Subject: Re: [TowerTalk] Dipole Height on the low bands
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Carlos:
There would be a few more parameters, but I don't think they will have a
bunch of influence. First, you should get a lobe that is about vertical
because of the reflection from the top of the building. The low-angle
lobes should be as predicted for an antenna of that height provided that
the antenna is high enough off the roof that the antenna can "see" the
ground at a depression angle that is equal to the radiation angle.
The other factor has to do with the surrounding terrain. The lobing
caused by ground effects are due to reflections from a flat earth.
Chances are that if you are on a building top, there will be other
buildings in the area. If the building density is really high like in
the downtown part of a major city, I don't think you can make the flat
earth assumption to predict the patterns. Of course this doesn't mean
that the antenna won't work well, you just won't be able to predict the
performance with the certainty that you would with a flat earth.
John
KC4ZXX
Carlos Augusto S. Pereira wrote:
>
> Dear friends,
>
> We all know that the height of a dipole over the ground deeply
> influences the take-off angle of a horizontaly polarized antenna. With a
> higher antenna we should expect a lower radiation angle. Right?
>
> Well, we also know that for 80m we need at least 1/2 wavelenght in order
> to obtain a 30 degrees angle. For that we need a very high tower! But if
> we install a dipole for 80 meters on the top of a very tall building?
> What happens? Can we expect a low angle or not, or there are more
> parameters involved on it?
>
> Thanks in advance,
>
> Carlos - PY1CAS
> E-mail: py1cas@ax.apc.org
>
> --
> FAQ on WWW: http://www.contesting.com/towertalkfaq.html
> Submissions: towertalk@contesting.com
> Administrative requests: towertalk-REQUEST@contesting.com
> Problems: owner-towertalk@contesting.com
> Search: http://www.contesting.com/km9p/search
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Date: Fri, 12 Sep 97 16:02:06 PDT
Sender: John Ferebee <jferebee@.dns.ultranet.com>
Subject: RE: [TowerTalk] Dipole Height on the low bands
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Hello Carlos:
Saw your message.
Our ham club station here in New York City is located in a
bldg that is about 350 meters high.
On certain bands the dipoles work like a house on fire. Big
signals. They are about 30 feet above the tower bldgs which
puts them about 100 feet above the main roof.
We have had many beams and they have worked very well. Now
we have a log as the other beams could not survice the
weather.
A Hy-Gain DX-88 vertical has worked quite well - out doing
many stations with beams in pileups to Europe and elsewhere.
We have a 1/2 wave and 5/8 wave(verticals) on 10 meters. At
the very tip of Long Island we get reports of 20/30 over 9
with 125 watts. More with the amp on of course.
On 160 we load the bldg as a shunt fed vertical and have the
radial wires up top. We do run max power with outboard audio
processing. We get, at times, 20-30 over 9 in Europe when
condx are good. We have no trouble working DX at all.
Our station is way down in the bldg and our 5 - 743 foot
feeders to the roof are 1 5/8" hardline so we don't really
have any loss re Andrew/Cellwave data sheets.
Our bldg is right on NY Harbor in lower Manhattan in NYC.
I have asked the same question but if you are high up and the
dipole is high above the main roof - they seem to play like
wild fire. If you have a tin roof, antenna not so high above
the roof it could be a different story however.
73, John
*****************************************
Name: John Ferebee
Radio: Talk Radio on 160 meters - W2CYA
Email: w2cya@broadcast.net
Company: Bell Atlantic, New York, NY
Voice: (212) 766-0411, (212) 429-8882
Fax: (212) 577-7426 - 24 hours
To: <towertalk@contesting.com>
Date: 09/12/97 Time: 16:02:06
*****************************************
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To: TOWERTALK@CONTESTING.COM, py1cas@ax.apc.org
To: <towertalk@contesting.com>
Date: Fri, 12 Sep 1997 17:50:58 -0600
Subject: Re: [TowerTalk] Dipole Height on the low bands
Message-ID: <19970912.202301.3254.1.N4KG@juno.com>
References: <34199B90.4AF1@ax.apc.org>
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From: n4kg@juno.com (T. A. Russell)
A dipole mounted on the roof of a tall building presents a complex
situation. The feedpoint impedance will likely be determined by
the height of the dipole above the roof (and conducting steel support
beams etc). The ground reflection will depend on how high and
close the the edge of the roof the antenna is placed.
If the antenna is mounted close to the edge, the ground reflection
in that direction will be from the earth below. If the roof is wide, the
reflection across the roof will be from the roof (high angle).
de Tom N4KG
............................
On Fri, 12 Sep 1997 16:44:16 -0300 "Carlos Augusto S. Pereira"
<py1cas@ax.apc.org> writes:
>Dear friends,
>
>We all know that the height of a dipole over the ground deeply
>influences the take-off angle of a horizontaly polarized antenna. With
>a
>higher antenna we should expect a lower radiation angle. Right?
>
>Well, we also know that for 80m we need at least 1/2 wavelenght in
>order
>to obtain a 30 degrees angle. For that we need a very high tower! But
>if
>we install a dipole for 80 meters on the top of a very tall building?
>What happens? Can we expect a low angle or not, or there are more
>parameters involved on it?
>
>Thanks in advance,
>
>Carlos - PY1CAS
>E-mail: py1cas@ax.apc.org
>
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To: TOWERTALK@CONTESTING.COM, py1cas@ax.apc.org
To: <towertalk@contesting.com>
Date: Fri, 12 Sep 1997 17:50:58 -0600
Subject: Re: [TowerTalk] Dipole Height on the low bands
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References: <34199B90.4AF1@ax.apc.org>
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A dipole mounted on the roof of a tall building presents a complex
situation. The feedpoint impedance will likely be determined by
the height of the dipole above the roof (and conducting steel support
beams etc). The ground reflection will depend on how high and
close the the edge of the roof the antenna is placed.
If the antenna is mounted close to the edge, the ground reflection
in that direction will be from the earth below. If the roof is wide, the
reflection across the roof will be from the roof (high angle).
de Tom N4KG
............................
On Fri, 12 Sep 1997 16:44:16 -0300 "Carlos Augusto S. Pereira"
<py1cas@ax.apc.org> writes:
>Dear friends,
>
>We all know that the height of a dipole over the ground deeply
>influences the take-off angle of a horizontaly polarized antenna. With
>a
>higher antenna we should expect a lower radiation angle. Right?
>
>Well, we also know that for 80m we need at least 1/2 wavelenght in
>order
>to obtain a 30 degrees angle. For that we need a very high tower! But
>if
>we install a dipole for 80 meters on the top of a very tall building?
>What happens? Can we expect a low angle or not, or there are more
>parameters involved on it?
>
>Thanks in advance,
>
>Carlos - PY1CAS
>E-mail: py1cas@ax.apc.org
>
--
FAQ on WWW: http://www.contesting.com/towertalkfaq.html
Submissions: towertalk@contesting.com
Administrative requests: towertalk-REQUEST@contesting.com
Problems: owner-towertalk@contesting.com
Search: http://www.contesting.com/km9p/search
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Subject: Re: [TowerTalk] Dipole Height on the low bands
Content-Type: text/plain
In-reply-to: Your message of Fri, 12 Sep 1997 16:44:16 -0300.
<34199B90.4AF1@ax.apc.org>
To: <towertalk@contesting.com>
Date: Fri, 12 Sep 1997 21:58:39 -0400
From: Pete Soper <psoper@encore.com>
Hello Carlos,
The biggest other parameter is metal in the building resonating with
the antenna. I built antennas on the electrical engineering building of the
university near here. The 40m antenna worked very well, but the 80m antenna
was "insane" with respect to its feedpoint impedance due to interaction with
the building. Another parameter is the presence of objects around the
building at various heights. If you are at the top of a building "by itself"
with the surrounding ground at normal height, fine. If you are at the top of
a building surrounded by other buildings, I don't think you'll see the
advantage you might wish for.
Regards,
Pete
KS4XG
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From: "L. B. Cebik" <cebik@utkux.utcc.utk.edu>
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To: "Carlos Augusto S. Pereira" <py1cas@ax.apc.org>
Subject: Re: [TowerTalk] Dipole Height on the low bands
In-Reply-To: <34199B90.4AF1@ax.apc.org>
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Carlos,
If the 80-meter antenna is installed on top of a tall building, there will
be some effect on the elevation angle of max radiation, but it is likely
to be small. Most of yur radiation going downward will miss the building
and hence the ground and other structures will be the major influences.
Using supports as high as possible on top of the building will help by
allowing more radiation to miss the roof. Many buildings do not have
metalic roof structures, and some of the radiation downward may also pass
through the roof to something lower before reflecting.
Hence, I suggest that it is certainly worth a trial antenna to check
results. Installing an antenna on the building top is easier than
erecting two high towers.
Good luck on the project.
-73-
LB, W4RNL
L. B. Cebik, W4RNL /\ /\ * / / / (Off)(423) 974-7215
1434 High Mesa Drive / \/ \/\ ----/\--- (Hm) (423) 938-6335
Knoxville, Tennessee /\ \ \ \ / / || / (FAX)(423) 974-3509
37938-4443 USA / \ \ \ \ || cebik@utk.edu
URL: http://funnelweb.utcc.utk.edu/~cebik/radio.html
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Date: Sat, 13 Sep 1997 10:49:33
To: py1cas@ax.apc.org
From: Pete Smith <n4zr@contesting.com>
Subject: Re: [TowerTalk] Dipole Height on the low bands
In-Reply-To: <34199B90.4AF1@ax.apc.org>
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At 04:44 PM 9/12/97 -0300, you wrote:
>Dear friends,
>
>We all know that the height of a dipole over the ground deeply
>influences the take-off angle of a horizontaly polarized antenna. With a
>higher antenna we should expect a lower radiation angle. Right?
>
>Well, we also know that for 80m we need at least 1/2 wavelenght in order
>to obtain a 30 degrees angle. For that we need a very high tower! But if
>we install a dipole for 80 meters on the top of a very tall building?
>What happens? Can we expect a low angle or not, or there are more
>parameters involved on it?
Hi Carlos -- I believe the right answer may be somewhere in between. At
the U.S. Department of State Radio Club, we used to have dipoles for 40 and
80 installed on top of a relatively small building, 40 m. above ground but
only 3-4 m. above a rooftop no larger than the length of the longest
dipole. They certainly did not perform like dipoles 3-4 m. above ground,
but they weren't as good as one might have hoped from their height above
ground. I had a similar experience at the 4U1WB (World Bank)club station
during the 1992 CW WPX contest.
My suspicion is that the antenna is really seeing two ground planes,
probably dominated by the one relatively far from the antenna, because the
Fresnel reflection zone at 80m. is thousands of meters from the antenna.
Still there are losses and reflections from conducting structures close to
the antenna, and its pattern reflects that too. You can model an
approximation with Mininec, which allows you to have several ground planes
of different heights as long as you make them concentric circles.
I hope this is helpful.
73, Pete Smith N4ZR
n4zr@contesting.com
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From: "Richard M. Manns" <rcc@kuentos.guam.net>
To: "'py1cas@ax.apc.org'" <py1cas@ax.apc.org>
Subject: RE: [TowerTalk] Dipole Height on the low bands
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Date: Sat, 13 Sep 1997 08:53:41 -0700
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Hi Carlos - you're right a lot of other factors come into play
1. Assume the building is 500 ft above sea level and the dipole is 40 ft above
the roof you are
now 540 ft above sea level so far so good.
2. The next question is the composition of the roof i.e. tin or concrete with
LOTS of rebar? What I'm getting
At is that the roof may well act like the soil in your area for it's electrical
characteristics and the net result
Being that of a similar dipole mounted on the ground resulting in the same
launch angle but in any case
My preference would be the tall building all other things being equal.
Gud luck es 73
Dick KH2G
-----Original Message-----
From: Carlos Augusto S. Pereira [SMTP:py1cas@ax.apc.org]
Sent: Friday, September 12, 1997 11:44 AM
To: towertalk@contesting.com
Subject: [TowerTalk] Dipole Height on the low bands
Dear friends,
We all know that the height of a dipole over the ground deeply
influences the take-off angle of a horizontaly polarized antenna. With a
higher antenna we should expect a lower radiation angle. Right?
Well, we also know that for 80m we need at least 1/2 wavelenght in order
to obtain a 30 degrees angle. For that we need a very high tower! But if
we install a dipole for 80 meters on the top of a very tall building?
What happens? Can we expect a low angle or not, or there are more
parameters involved on it?
Thanks in advance,
Carlos - PY1CAS
E-mail: py1cas@ax.apc.org
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Date: Sat, 13 Sep 1997 11:12:53 -0700 (PDT)
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Subject: Re: [TowerTalk] Dipole Height on the low bands
To: py1cas@ax.apc.org
In-Reply-To: <34199B90.4AF1@ax.apc.org>
X-Mailer: SPRY Mail Version: 04.00.06.21
Good afternoon, Carlos.
The 80 dipole will be affected by the roof and how close the dipole is to
the edge of the roof. I have had rotatable 80 mtr dipoles on two roof tops
on Dxpeditions. The last one was XZ1N.
The best location for the dipole is right at the edge of the roof. The
dipole is parallel to the side of the building. If you can get the dipole
out, over the edge of the building, it will be best.
Having a rotatable 80 was good for testing. When the dipole was rotated so
part was over the roof, the VSWR changed very much. This indicates the
dipole is coupling to the roof - not good! The rotatable dipoles were about
16' above the roof (80 mtrs).
The next best is to have the dipole very high above the roof. This will
minimize the coupling to the roof. A height of 30' might be all right.
The roof is a lot of steel. It also has wiring, etc. This means it can act
as ground. Yes, the ground reflection zone is beyond the roof; however, the
roof is in the near field.
Have a good day and 73,
Tom, N6BT
Force 12 Antennas and Systems
(Home Page http://www.QTH.com/force12 )
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