40 meter Antennas
This is a 5 element home brew 40 meter beam at 125 feet. It has a 60 foot
supported boom comprised
of sections of eight inch square aluminum tower. This
is an OWA (Optimized wideband antenna) based on the original OWA design by NW3Z. I did model this antenna
and make the adjustments for operation on 40 meters. With this full size antenna
array it is not
a 'cut and try' effort; it is best if it works the first time.
This 40 meter beam will cover the complete 40 meter band with less than 1.2:1 SWR. The OWA feed is 50 ohms. You can tune this antenna on the sawhorses - well not quite as the elements sag six feet. You get a 50 ohm feed by bringing in the first director closer to the driven element.
The elements construction utilizes a 2.5 inch aluminum pipe at the center of the element and with pipe/tubing which gradually tapers down to 0.5 inch tubing at the tips. All material has a yield of 40KPSI. I utilized a spread sheet to calculate the strength of the elements at a given wind speed.
The actual antenna tuned to within 50 kHz of the modeled antenna on Eznec.
The antenna is rotated at 1/3 of an rpm by a home brew rotator mounted at the 110 foot level. A shock absorber/damper is used between the rotator and the mast to minimize the effects of any sudden stops and starts. Even at 1/3 rpm it will take this antenna 10 seconds to fully stop. It is fed with 7/8 inch and 1/2 inch foam heliax as the antenna is located some 400 feet from the building. It has been up for seven years and works well. As you can see in the picture the feed point is some twenty feet along the boom so it is not something you reach while standing on the tower. If something goes wrong with the feed then it is 'I walk the line' or is it 'I walk the boom'!
If you require additional data on this antenna is available by contacting me on email.