On Sun, 18 Apr 2004 18:10:13 GMT, zeno wrote:
Hi Richard,
I think at least one of the metal masts I will be using to hang the 160m
loop might lend itself to the vertical antenna you suggest.
Hoist wire for the rest! After all, you are already doing that aren't
you?
It is the one
that is a full 50' in height, and will be out in the middle of the
orchard where ground radials can be installed easily. Unfortunately this
particular mast is the one farthest away from the shack, approx. 500
feet.
Questions:
1. For reference purposes, what is the exact description (name) of this
vertical? Any recommendations for information in print about this
concept?
Folded Unipole (N. O. L.);
Type UG;
NORD;
Triangular Folded Unipole (VOA aboard the USCGC Courier)
"The Amateur Radio Vertical Antenna Handbook," Capt. Paul H. Lee, N6PL
2. What band, or bands, would it be good for? (Assuming the guy wires are
generally in the position of effectivenes as guy wires.)
Folded Triangular Unipole is 45 feet tall and rated from 3 to 10.5 MHz
NORD 30 feet tall and rated from 2 to 4 MHz;
Folded NOL Unipole is 0.124 wavelength tall;
Type UG is 0.048 wavelength tall.
3. Would it be monoband, tuned to an exact f, or possibly multiband?
Depends on antenna type and number of guy wires. The devil is in the
details as the saying goes.
4. Where would one attach the feed line and would a run of 500' to the
shack still be worth the effort?
At the base. Run an exciter to a remote amp. That is, put your loss
into the cheapest signal to boost. Move the shack ;-)
5. If I understand, the antenna is comprised of the mast itself (with
telescoping sections securely and electrically bonded to each other) plus
the "extension" of calculated lengths of the four guy wires, utilizing
insulators at precise points before being attached to ground anchors.
Exactimundo.
6. How would the mast be mounted to the ground? Should it ideally be
isolated from ground or contiguous with the ground? Theortically I could
build a short wooden platform or something.
Folded Unipoles (which are wide band within the band of interest and
some bands are very wide) are fed with their base at ground potential
(add radials here). The feed point is through a cap, up the drop
wire. that is descending from the conductive (half) yard arm.
The other types are fed in series (the base insulated from ground).
Comparisons should be studied. If building an insulated base is no
problem, shorting it to ground becomes an easy option.
7. Other than the mast itself, the four guy wires, and some kind of
system of radials in the ground, are there any other elements to this
antenna that I should know about or be thinking about?
Don't forget the drop wire. Search the web for Folded Unipoles
(verticals) for illustrations to make this clearer. There is also a
series cap to tune it. It is basically a very big gamma match.
By varying the diameter of the drop wire to the mast diameter, you get
transformer action that boosts or lowers the feedpoint R. As most of
these are very short antennas with very low radiation resistance, the
wire diameter to mast diameter ratio often boosts that value to 50
Ohms without too much problem.
WARNING, this boost does not raise efficiency! That remains a
function of the radiation resistance compared to structure Ohmic loss
and ground loss. The feed point R is simply a boosting of BOTH the
radiation resistance AND those loss Rs too.
73's
Richard Clark, KB7QHC
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