2/3 BOBTAIL CURTAIN anyone tried ?
Cecil Moore
Karl Martin Gjestrum <kytd...@applause.no> writes:
>Anyone tried it? It should be a number of fased verticals depending of
>how many vertical elements you hang on.
A lot of people know this antenna as the "Half Square" sold
by Antennas West. They also have an application note on it.
It is a good low-angle, bi-directional antenna if you have
a good ground to go with it. IMO, if you don't have a good
ground, you would be better off with a delta loop like the
one I'm putting up. It requires exactly the components of
the "Half-Square" in a slightly smaller area.
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For 40m, top section is about 64ft, sides are about 40ft.
It is fed with 50ohm coax on a side approximately 8ft
down from the top. If you put pulleys at the top ends,
you can adjust the form factor and feedpoint for optimum
results.
73, Cecil, W6RCA, OOTC
mike....@ziplog.com
In <32577A...@applause.no>, Karl Martin Gjestrum <kytd...@applause.no> writes:
>Found this antenna in a magazine
>Anyone tried it? It should be a number of fased verticals depending of
>how many vertical elements you hang on.
> best 73 de LA7EJA
>
>
>
> 1/2 wave
>_________________________________ 50 ohm coax here
>| |
>| |
>| |
>| |
>| 1/4 wave | 1/4 wave
>| |
>| |
I ran it off an entertainment hall jutted out into the Gulf of Mexico in Galveston
as part of an entry into a science fair project in high school. That was in
1952, if my memory is right. The pier was about 45 feet over the water,
depending of course, on the time of day and the tide. I tied the two elements
to the wood pier piling railings and dangled them down with tools for weights
on the ends. I fed it with coax, as you describe from a pair of 4-65a's.
Had to re-tune it during the day as the sea level rose and fell, as I recall...
It did a WONDERFUL job, however, as a kid at 13, I really didn't know
enough to understand exactly what salt water was worth. Even with an
Extra Class back then, I really didn't appreciate the math, let alone the
political overtones of a good DX expedition, nor did I understand public
opinion. I did learn a little bit about Dr. R. F. Burns and artificial grounds
that I had to string to calm the pounding RF sea above....
It has been argued as late as yesterday that I still don't understand all
this, on all counts, for I still get burned in various ways....
The first place winner of the science fair put out only 300 watts into hi-fi
audio, where I put about the same amount into what I thought was a far
better place. I did get a third place.... behind a medicine show. One of the
judges took me aside afterward and said, "Son, its hard to follow a dog act!"
:)
Extrapolating this to your question, I'm guessing that you have a curious
top-down perspective of the ground, like I did when I got there! My use
of the creature was out of necessity. Are you an apartment dweller?
If so, the ground below should be much more stable than mine was. Once
tuned up you will likely get to use it without much fiddling.
If you don't have this curious perspective of height, or something like that,
I'd feed it from the bottom as a voltage fed device from a tuner, like they
normally get fed. No sense getting heated up over all this foolishness!
:)
Incidentally, this is a vertical element device. (Now, really?) :)
That means it will interact with everything else around it that is vertical,
metal, and is either bigger or littler than it! Bigger dogs can scent it right
quick! In the reverse, if it too close to any of your littler metal trees that
think they are tough stuff, it's just a bigger dog!
Where verticals are involved, one dog is a pet; two dogs can be dogs...
:)
//-----------------------------
Mike - W5WQN
Mike....@ziplog.com
MIke....@f3000.n117.z1.fidonet.org
Karl Martin Gjestrum
Merv Stump
This antenna is often referred to as a "Half-Square". It works well so
long as you have a good ground. Regards, Merv
Cecil Moore
David wrote:
> I don't have a ground system for my version of the 20 M 1/2 SQ as shown
> in the 73 article.
Dang David, where the heck do you live that doesn't have a
ground system? :-)
Gary Coffman
In article <xJOyNa6.c...@delphi.com> Cecil Moore <cecil...@delphi.com> writes:
>Karl Martin Gjestrum <kytd...@applause.no> writes:
>>how many vertical elements you hang on.
>
>by Antennas West. They also have an application note on it.
>It is a good low-angle, bi-directional antenna if you have
>a good ground to go with it. IMO, if you don't have a good
>ground, you would be better off with a delta loop like the
>one I'm putting up. It requires exactly the components of
>the "Half-Square" in a slightly smaller area.
>
> +------------------------------------+
> \ /
> \ /
> \ /
> \ /
> \ /
> \ /
> \ /
> \ /
> \ /
> ++
>
>For 40m, top section is about 64ft, sides are about 40ft.
>It is fed with 50ohm coax on a side approximately 8ft
>down from the top. If you put pulleys at the top ends,
>you can adjust the form factor and feedpoint for optimum
>results.
>
>73, Cecil, W6RCA, OOTC
Ok, dumb question time. What exactly are the advantages of this
antenna form over a couple of plumb vertical elements fed out
of phase? And why should we want to build it instead of just
using the top section as a dipole? IE does it really have
significant gain or pattern advantages over the simpler dipole?
Gary
--
Gary Coffman KE4ZV | You make it, | Due to provider problems
Destructive Testing Systems | we break it. | with previous uucp addresses
534 Shannon Way | Guaranteed! | Email to ke...@radio.org
Lawrenceville, GA 30244 | |
Cecil Moore
Gary Coffman <ga...@ke4zv.atl.ga.us> writes:
>Ok, dumb question time. What exactly are the advantages of this
>antenna form over a couple of plumb vertical elements fed out
>of phase? And why should we want to build it instead of just
>using the top section as a dipole? IE does it really have
>significant gain or pattern advantages over the simpler dipole?
I don't have a good natural ground and I don't want to
put down 120 radials per vertical.
The vertical delta loop gives a gain of about 3.5dBi at a
take-off-angle of 17deg on 40m when fed on a side. That
broadside gain is better than phased verticals with no
good ground. At TOAs less than about 25deg, the delta
loop has gain over a dipole at 37ft and is better for
DX. It also has a horizontal beamwidth of 2x100+ degs.
It's as easy to errect as a dipole with a TOA of 75 degs
and it's a heck of a lot easier to build than phased
verticals with 100 radials each. It is also a decent
antenna on 20m, 15m, 12m, and 10m. By breaking it at
the halfway point, it becomes an almost omnidirectional
75m antenna, similar to a full-sized vertical.
I started looking at rectangular antennas as suggested
by Kurt S. in his column. For my purposes, the above
delta loop is better and may be less lossy since there
are no long horizontal runs near the ground. Anybody
who has EZNEC and UUDECODE and wants my 40mdelta.ez
file, I'll be glad to email it to you.
73, Cecil, W6RCA, OOTC
Cecil Moore
Gary Coffman wrote:
> What exactly are the advantages of this antenna form...
Hi Gary, one other big advantage that this has over other
antennas is it is end-fed, i.e. close to the shack/house.
For all the people struggling with RF problems from end-fed
"long-wires", a delta-loop solves the problems of feedline
radiation, RF in the shack, etc. because it is a closed loop.
Assume a person has a 60ft end-fed with the braid floating.
Hanging an 80ft drooping wire from the braid to the other end
of the "long-wire" will result in a good 40m antenna free of
grounding problems and it will work on 20m, 15m, 12m, 10m (and
even 75m by breaking the loop in the center).
73, Cecil, W6RCA, OOTC (not speaking for my employer)