Wire beams do indeed work. Inverted Vee versions of the same beams also
work, but with reductions in gain and a wider beamwidth than the same
design level at the highest point of the Vee. Vees may not optimize at
the same element lengths as a level element beam, so they should be
designed and tested in advance to get the desired results.
As with all 40 meter beams, the higher the better. Most horizontal
antennas begin to show their merits when 1/2 wl or higher, which is a
pretty good reach on 40 meters and field operations. At lower heights,
the pattern vetically takes on a egg shape with the big end up at an angle
peaking at 35 to 45 degrees, depending on height. Vee beams, with the
ends considerably lower have corresponding higher elevation angle
characteristics. A level Yagi at 1/2 wl has a main lobe elevation angle
of about 23/24 degrees, for the comparison.
However, even a little gain and F-B can be an advantage, assuming the
antenna is pointed where it will be most useful. By making both elements
the right length for a driven element and using a transmission line stub
to lengthen the "second" element into a reflector, you can use a simple
switching system to make the beam reversible.
If you have the time, you may wish to consider other designs, such as the
Moxon rectangle, parasitical half squares, and numerous others. Most can
be made reversible as wire beams. You may also wish to consider scaling
up the Field Day Special, a ZL Special version by W7EL, that appeared some
years ago in QST--uses 300-Ohm twinlead throughout with 1/2 wl stubs for
reversal of direction.
However, in the process of design for 40, remember to devote considerable
effort to getting the antenna as high as possible (safely, of course).
L. B. Cebik, W4RNL /\ /\ * / / / (Off)(423) 974-7215
1434 High Mesa Drive / \/ \/\ ----/\--- (Hm) (423) 938-6335
Knoxville, Tennessee /\ \ \ \ / / || / (FAX)(423) 974-3509
37938-4443 USA / \ \ \ \ || firstname.lastname@example.org
FAQ on WWW: http://www.contesting.com/towertalkfaq.html
Administrative requests: towertalk-REQUEST@contesting.com