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