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Old March 5th 11, 07:10 PM posted to rec.radio.amateur.antenna
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Default Trap Vertical Antenna Questions

It would work, but the lower radials would have to
be spread apart to avoid coupling issues.
One could also just hang a second trap vertical as
the lower half of the antenna..
But, being I am a radio bully, I tend to avoid trap
antennas. Hustler verticals are pretty lossy on the
lower bands when you factor in the loss of the traps,
and then the upper level loading coil required to
resonate the thing.
If I were to use a commercial antenna to do what
you propose, I think I would prefer a Butternut over
the Hustler. :/
But anyway, what you want to do will work, but it
would be best to angle the radials a bit away from
each other to minimize coupling and the tuning
difficulties you would see if they are very close
to each other.
Also, the amount of ground loss will depend on the
antennas height in wavelength. So I wouldn't expect
gangbuster performance on the low bands unless the
antenna is very high. And how high must be determined
for each band measured in wavelength. High on 10m,
might almost be considered on the ground on say 80m.
So the amount of radials needed for an equal amount
of ground loss will very greatly to the frequency.
So if say the whip base is at 20 feet in the tree, and
you are hanging an 8ft radial for 10m, the performance
should be fairly decent. The antenna is up at nearly 3/4
wavelength, and one radial will do well.
But on 80m, 20 ft is just barely off the ground at
less than 1/10 WL high and the tree is not even tall
enough to hang it vertical. It would need to be run out
at an angle, and with only one radial at that low height
in WL, performance is going to be lame.
Of course, if you can mount it higher, the frequency
where lameness creeps in will slowly drop as you get higher.
:/
If I wanted to work all bands, I'd use the tree as a
support for an all band horizontal dipole.
Or even better, parallel fed full size dipoles, which
is what I usually run.
It would do a better job in the overall scheme of
things. You would have a semi decent NVIS pattern on
the low bands, and still be able to work some DX.
With stunted vertical on the low bands, NVIS performance
will be pretty lame. Many of the guys just running
plain Jane low coax fed dipoles will be kicking sand in
your face on the shorter lower band paths. :|




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Old March 6th 11, 05:22 AM
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Location: Tampa florida
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Default

Quote:
Originally Posted by View Post
It would work, but the lower radials would have to
be spread apart to avoid coupling issues.
One could also just hang a second trap vertical as
the lower half of the antenna..
But, being I am a radio bully, I tend to avoid trap
antennas. Hustler verticals are pretty lossy on the
lower bands when you factor in the loss of the traps,
and then the upper level loading coil required to
resonate the thing.
If I were to use a commercial antenna to do what
you propose, I think I would prefer a Butternut over
the Hustler. :/
But anyway, what you want to do will work, but it
would be best to angle the radials a bit away from
each other to minimize coupling and the tuning
difficulties you would see if they are very close
to each other.
Also, the amount of ground loss will depend on the
antennas height in wavelength. So I wouldn't expect
gangbuster performance on the low bands unless the
antenna is very high. And how high must be determined
for each band measured in wavelength. High on 10m,
might almost be considered on the ground on say 80m.
So the amount of radials needed for an equal amount
of ground loss will very greatly to the frequency.
So if say the whip base is at 20 feet in the tree, and
you are hanging an 8ft radial for 10m, the performance
should be fairly decent. The antenna is up at nearly 3/4
wavelength, and one radial will do well.
But on 80m, 20 ft is just barely off the ground at
less than 1/10 WL high and the tree is not even tall
enough to hang it vertical. It would need to be run out
at an angle, and with only one radial at that low height
in WL, performance is going to be lame.
Of course, if you can mount it higher, the frequency
where lameness creeps in will slowly drop as you get higher.
:/
If I wanted to work all bands, I'd use the tree as a
support for an all band horizontal dipole.
Or even better, parallel fed full size dipoles, which
is what I usually run.
It would do a better job in the overall scheme of
things. You would have a semi decent NVIS pattern on
the low bands, and still be able to work some DX.
With stunted vertical on the low bands, NVIS performance
will be pretty lame. Many of the guys just running
plain Jane low coax fed dipoles will be kicking sand in
your face on the shorter lower band paths. :|
I can get a Hustler 4BTV locally here in Tampa cheap is why I mentioned it. I too prefer a Butternut! How about a commercial wire trap dipole for 10 through 40 meters hung vertically instead ?
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Old March 6th 11, 07:03 AM posted to rec.radio.amateur.antenna
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Default Trap Vertical Antenna Questions

On Sun, 6 Mar 2011 04:22:28 +0000, ka7niq
wrote:

How about a commercial wire trap dipole
for 10 through 40 meters hung vertically instead ?


Hi OM,

Actually, many. Look at the GAP line of antennas (I have the Eagle).

73's
Richard Clark, KB7QHC
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Old March 6th 11, 05:25 PM
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A wire trapped dipole would be easier to hang vertically in a tree.
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Old March 6th 11, 06:35 PM posted to rec.radio.amateur.antenna
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Default Trap Vertical Antenna Questions

On Sun, 6 Mar 2011 16:25:12 +0000, ka7niq
wrote:

A wire trapped dipole would be easier to hang vertically in a tree.


Hi OM,

There are at least two difficulties with this - even though it sounds
eminently simple.

One, the two arms of the dipole have an uneven balance with ground.
This means that given the typical configuration of trap design and
placement, that the traps on each side must be different to account
for the lack of symmetry. In an ordinary horizontal placement, this
is not a problem.

Two, the standard advice for the feedline in a horizontal dipole is
that it drop away at a right angle for at least a quarterwave before
being turned in its route toward the shack. Well, the feedline still
has to drop away from the feedpoint, but with the antenna vertical,
this means it has to first move horizontally a quarterwave before
dropping and THEN turning towards the shack. This is unlikely to be a
practical construction, or you would have simply put up the dipole
horizontal in the first place.

The feedline trailing down alongside the lower arm of the vertical
dipole is going to seriously interfere with tuning and launch angle.
In a sense, it will be shorting out any traps in that arm.

This is why I offered the GAP line of products as an example of a
vertical dipoles. They are not the only line that offer a solution to
the problem of the feedline proximity. What they do is route the
feedline up INSIDE the lower dipole arm. Physics insures that the
inside of the arm is shielded from the outside. However, there is
still the problem of coupling at the lower tip (where the line enters
to go up). GAP puts a W2DU style choke there.

Now, as to your point of "hang vertically in a tree" suggests that the
GAP style antenna would be hung from its upper tip, rather than
mounted (electrically isolated too) at its lower tip. I'm sure you
could come to terms with that.

73's
Richard Clark, KB7QHC
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