These antennas are designed by Kent Britian, WA5VJB
If your planning to build an EME array, don't use these antennas. But, if you want to put together a Rover station with less than $500 in the antennas or just want a good antenna for the home, read on.
These antennas are relatively small, easily constructed from common
materials/tools and have surprising performance. The feed method is greatly
simpified by directly soldering the coax to the driven element. No baluns
or gamma matches are used in this design. This simplified feed uses the
structure of the antenna itself for impedance matching. The spacing of
the director and reflector elements from the driven element directly affects
the feed point impedance of the antenna. So, the design starts with the
feed (driven element) and the elements are built around it. Typically,
a high gain antenna is designed in the computer, then you try to come up
with a matching arrangement for a 31.9 Ohm feed! For the cost about 0.5
dB of gain, these antennas make some design compromises for the feed impedance,
use an asymmetrical feed and make trade offs for a very clean pattern.
But, they allow simple measurements, have wide bandwidth, the ability to
grow with the same element spacing AND... you can build these antennas
for $5!!!! [W0FMS note:
$15 is more typical if you have to buy the wood and brass rods]
The booms used for these antennas is 1/2" X 3/4" wood. The elements have been made from silicon bronze welding rod, aluminum rod, hobby tubing and solid ground wire with no change in performance. Since you want to be able to solder to the driven element, silicon bronze welding rod, hobby tubing and #10 or #12 solid copper wire have been used and work fine.[W0FMS note: The brass rod is rather difficult to solder to, I recommend the #10 solid copper]A drop of "Super Glue", epoxy or RTV is used to hold the elements in place. [W0FMS Note: I use "push-nuts" or "speed-nuts" for this, and no glue] A good coat of Polyurethane should be applied to the wooden boom to protect it from the weather. A polyurethane varnished 902 MHz version has been in the air for a year now with little deterioration in performance.
And now for the antenna designs. These antennas have been carefully
designed to have the highest dB's/Dollar ratio of anything around. They
were designed with YagiMax, tweaked using NEC and the driven elements experimentally
determined on the antenna range. The driven element design is the same
for all frequencies except for the length (L) and separation (H).
Dimensions for other antennas:
144, 223, 432, 435, 902, 1296 MHz Cheap Yagi dimensions