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Old August 6th 03, 01:59 AM
Kristinn Andersen
 
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Default Poor vertical performance on metal sheet roof - comments?

I just finished putting up a 6m long aluminum tube for a vertical for
10/15/20m. Its length is just over 1/4 wavelength on 20m and just
under 5/8 wavelengths on 10m. The vertical is located at the apex (8m
above ground) of a sheet metal roof top, that slopes approx. 30
degrees down to all sides from the vertical. I use use the roof metal
as a counterpoise and feed the vertical with an autotuner at the base.
A coax runs 6m (18ft) from the autotuner, down through an attic
window and to my TX.

Now, simulations (EZNEC 3.0) and common wisdom predict a fairly good
performance for this antenna. Not so. When the tuner is set for 1:1
VSWR the RX signals from the vertical on 15m are consistently 4
S-units below a 20m (60ft) long sloper at the corner of the house. I
use this sloper for 160m and 80m. When going to the 20m band the
vertical is about 8 S-units below the sloper. Even more irritating,
the vertical is constantly outperformed by a leftover horizontal wire,
approx. 6m long, lifted only 1m (3ft) above the roof.

Switching to the vertical from either wire antenna the background
noise and signals drop noticably. This led me to check out the tuner,
the feedline, connections, but all seems to be fine. The bottom line
appears to be that the vertical is simply a much poorer antenna than
either of the wires I have up already - contrary to the theory and
conventional wisdom.

Any comments, anyone, before I remove the vertical and turn to another
design?

73 de TF3KX, Kristinn

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Old August 6th 03, 02:11 AM
H. Adam Stevens
 
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"Kristinn Andersen" wrote in message
om...
I just finished putting up a 6m long aluminum tube for a vertical for
10/15/20m. Its length is just over 1/4 wavelength on 20m and just
under 5/8 wavelengths on 10m. The vertical is located at the apex (8m
above ground) of a sheet metal roof top, that slopes approx. 30
degrees down to all sides from the vertical. I use use the roof metal
as a counterpoise and feed the vertical with an autotuner at the base.
A coax runs 6m (18ft) from the autotuner, down through an attic
window and to my TX.

Now, simulations (EZNEC 3.0) and common wisdom predict a fairly good
performance for this antenna. Not so. When the tuner is set for 1:1
VSWR the RX signals from the vertical on 15m are consistently 4
S-units below a 20m (60ft) long sloper at the corner of the house. I
use this sloper for 160m and 80m. When going to the 20m band the
vertical is about 8 S-units below the sloper. Even more irritating,
the vertical is constantly outperformed by a leftover horizontal wire,
approx. 6m long, lifted only 1m (3ft) above the roof.

Switching to the vertical from either wire antenna the background
noise and signals drop noticably. This led me to check out the tuner,
the feedline, connections, but all seems to be fine. The bottom line
appears to be that the vertical is simply a much poorer antenna than
either of the wires I have up already - contrary to the theory and
conventional wisdom.

Any comments, anyone, before I remove the vertical and turn to another
design?

73 de TF3KX, Kristinn


Kristinn
Can you get on the roof with an antenna analyzer and see what the vertical
looks like to the tuner?
Are you certain the roof is electrically continuous?
H.
NQ5H


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Old August 6th 03, 02:16 AM
K9SQG
 
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Kristinn,

I'd try measuring SWR and impedance at the base of the antenna and also ensure
that connections to the roof, particularly between the various sections, all
have good cotinuity. There is a chance that there is rust and corrosion
between overlapping sections.

73s,

Evan
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Old August 6th 03, 02:44 AM
Yuri Blanarovich
 
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Any comments, anyone, before I remove the vertical and turn to another
design?

73 de TF3KX, Kristinn



First I would check the coax and tuner performance, make sure you have no bad
connections.
When comparing signals against other antennas, keep in mind that vertical is
better performer at low angles - DX. Try the comparison on DX signals rather
than Eu and high angle propagation. You could esay see 20 dB differences, but
check at the beginning of openings to DX areas and see how they compare.

GL Yuri, K3BU
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Old August 6th 03, 04:27 AM
W5DXP
 
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Kristinn Andersen wrote:
Any comments, anyone, before I remove the vertical and turn to another
design?


I spent considerable time and effort erecting a 33ft vertical 40m
antenna with 8 elevated radials at 20ft. Average signal strengths were
about 2 S-units below a dipole and the noise level was about 2 S-units
higher than the dipole. At my QTH, it was a dog.
--
73, Cecil http://www.qsl.net/w5dxp



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Old August 6th 03, 05:13 AM
Tarmo Tammaru
 
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Kristinn,

Before you decide to remove it, I would see if it can be made to resonate on
20 meters by itself. Ditch the tuner, and see how it performs. As somebody
suggested, see what it does with a ZL or VK, or even W6. I never had any
luck with 20m verticals myself, but talked to an G station on 20 SSB a few
days ago who was using one; sounded fine.

BTW, here is an odd one. I once had a 40 meter vertical with the feedpoint
at about 30 feet and 4 radials, sloping down at about 45 deg. At the same
time I had a 40m dipole at about 50 feet. I made tests with two groups of
hams. The one group was about 400 miles away, the other group about 1100
miles. Without exception, in each group people with verticals preferred my
vertical, and people with horizontal antennas preferred my dipole. Yes, I
know all about polarization not being important for a skywave signal.

Tam/WB2TT
"Kristinn Andersen" wrote in message
om...
I just finished putting up a 6m long aluminum tube for a vertical for
10/15/20m. Its length is just over 1/4 wavelength on 20m and



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Old August 6th 03, 10:47 AM
Roy Lewallen
 
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Mark Keith wrote:
. . .
Also, I suspect excess loss if the noise and signals drop compared to
any other antenna. If the coax is not bad, old or waterlogged, or thin
stuff like rg-58, then I'd suspect excess loss in the autotuner. . . .


Out of curiosity, just how much loss do you think "thin stuff like
RG-58", say 50 feet of it, has on 20 meters?

Roy Lewallen, W7EL

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Old August 7th 03, 03:38 PM
Jeffdeham
 
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W5DXP wrote in message ...
Kristinn Andersen wrote:
Any comments, anyone, before I remove the vertical and turn to another
design?


I spent considerable time and effort erecting a 33ft vertical 40m
antenna with 8 elevated radials at 20ft. Average signal strengths were
about 2 S-units below a dipole and the noise level was about 2 S-units
higher than the dipole. At my QTH, it was a dog.


I had exactly the opposite results. It was 2-3 S units better at low
angles of radiation compared to my low dipole. I've heard other
experiences like this too. I just wonder if there some part of antenna
theory that's missing that could explain why that happens. Murphy's
law, blind luck, who knows. 8-)

73!

Jeff
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Old August 7th 03, 03:53 PM
Voice In Wilderness
 
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For horizontal antennas -- the radiation angle becomes lower as the height
of the antenna increases and vice versa (with caveats)
A layman's explanation at URL:
http://www.signalengineering.com/ult...radiation.html

Excuse the CB reference -- but it has some nice pictorials.

Those mathematically inclined can model antennas at URL:
http://www.eznec.com/

================================================== ====

"Jeffdeham" wrote in message
om...
W5DXP wrote in message

...
Kristinn Andersen wrote:
Any comments, anyone, before I remove the vertical and turn to another
design?


I spent considerable time and effort erecting a 33ft vertical 40m
antenna with 8 elevated radials at 20ft. Average signal strengths were
about 2 S-units below a dipole and the noise level was about 2 S-units
higher than the dipole. At my QTH, it was a dog.


I had exactly the opposite results. It was 2-3 S units better at low
angles of radiation compared to my low dipole. I've heard other
experiences like this too. I just wonder if there some part of antenna
theory that's missing that could explain why that happens. Murphy's
law, blind luck, who knows. 8-)

73!

Jeff



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Old August 7th 03, 04:49 PM
W5DXP
 
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Jeffdeham wrote:
I had exactly the opposite results. It was 2-3 S units better at low
angles of radiation compared to my low dipole. I've heard other
experiences like this too. I just wonder if there some part of antenna
theory that's missing that could explain why that happens. Murphy's
law, blind luck, who knows. 8-)


The vertically polarized noise in my neighborhood is the real killer
of verticals.
--
73, Cecil http://www.qsl.net/w5dxp



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