[Top] [All Lists]

[CQ-Contest] Antenna Software Modeling

Subject: [CQ-Contest] Antenna Software Modeling
From: w5hvv@aeneas.net (Roderick M. Fitz-Randolph)
Date: Fri Apr 11 01:03:53 1997
This is a request for some help from those that have access to
antenna modeling software.  I have wondered for some time why
the following idea wouldn't work and work well.

Envision 2 vertical antennas for 75/80 meters separated by
whatever is the best compromise for the situation (1/8 Wave?
3/16? 1/4?).  The forward one (in the direction of the desired
signal strength) would be cut for 3795 kHz or thereabouts; the
rearward vertical cut for 3525 kHz.  When using the rear one
(for CW) the forward one would act as a directive parasitic
element.  When using the forward one (for SSB) the rearward one
would act as a reflective parasitic element.  No phasing harnesses,
nothing exotic.... just a relay at the base of each that would
"make" when using that frequency and be "open" when using the
other element. Variations on the theme of W5HVV would be to ground
the parasitic element to the counterpoise, which might have a very
beneficial effect and, again, could be easily accomplished by the
same relay (SPDT).  This approach could be used in four directions
around a tower and be switch selectable.  The rearward element would
be approximately 7.66% larger than the forward one.

Anyone game to try their EZNEC or whatever software on this one?
It seems to me that it would be possible to support 2 vertical
wires from dacron (or whatever) rope hoisted at one end in a tall
tree or tower (mine is 130 feet tall so would easily perform the
operation) and a tree or whatever at the other end.  Come to think
of it, the right sized tower could act as a reflector for the CW
driven element .... and you'd have a 3 element beam.  Surely this
has been done before, or has it?  Don't think I've ever run across
this combination, to my best recollection.

Here is a graphic:     80 M
                                  75 M
                         |         |
                         |         |
                         |         |  ----> Direction of Max Sig.
                         |         |
                         |         |
                         |         |
                         |         |

Secondly, I've noticed that most "Inverted L" antennas in the books
and articles are only a quarter wave in length.  Why is this?  Isn't
there some considerable gain to be had in making them 3/4 wavelength?
My first Inverted L antenna was a 40 meter job that was 1/4 wave
vertically and 1/2 wave horizontally.  It afforded both vertical and
horizontal components to the received and transmitted signal.  It
played very well for Stateside contacts and did a very reasonable
job on DX contact.  A variation on this would be to make it a 1/2 wave
vertical with a 1/4 wave horizontal component at the top.

Both of these will provide a low impedance feedpoint, I believe (in the
30 ohm region?) and would give a substantial advantage over the typical
1/4 wave vertical.  It would have both omin-directional characteristics
and "broadside" (to the horizontal component) characteristics.  The
halfwave vertical component could certainly be sloping if height became
a major problem.  Again, I've not run across anything quite like this
in print in a long, long time (if ever) and to the best of knowledge,
it hasn't been modeled and compared to the characteristics of a 1/4 wave
veritical regards gain, etc.

Anyone game to do these two concepts and put it on the Reflector?

73, es best DX...  Rod, W5HVV

CQ-Contest on WWW:        http://www.contesting.com/_cq-contest/
Administrative requests:  cq-contest-REQUEST@contesting.com

<Prev in Thread] Current Thread [Next in Thread>
  • [CQ-Contest] Antenna Software Modeling, Roderick M. Fitz-Randolph <=