Ve6fi Amateur Radio

40 meter Antennas

This is a 5 element home brew 40 meter beam at 100 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 1/2 of an rpm by a Alfa Spid Big Rak rotator mounted at the 90 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 1/2 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 it is available by contacting me on email.

 

ANOTHER 40M BEAM

We do not have the Log antenna up at this new location so I thought I would build a 3 element 40m beam in the interim. Below are

some of the fabrication details.  I modeled this antenna with Ezenec and the end results correlated almost exactly to the model.  Usually I build the antennas as an OWA where the Driven Element and the first director are spaced close together to get the matching to fifty ohms. I wanted to make the antenna symmetrical and I wanted to have it balanced for wind load. With the model, at the height I selected, that I could offset the DE by two feet off of the center and have a 50 ohm match. I set the DE two feet from the center of the beam and then connected a counter weight near the director to balance the antenna. Now I had an antenna with center of gravity at the center of the boom and had the boom balanced for wind load. The measured SWR was less than 1.5:1 across the 40M band.

 If you require additional data on this antenna it is available by contacting me on email.

 

Below is the 40M 3 element antenna on the ground. The boom is 4 inch AL and the elements start out as 1.5 inch pipe.

 

 

Below is the boom to reflector interface. I had the boom parts from another project so decided to make use of what I had.

 

 

Below is the boom to Driven Element interface. The DE is a dipole so there is a fiberglass insert in the center of the driven element.

 

 

 

Below is the 40M beam bolted onto the side of the tower. The tower has a 32 inch face and is part of the twin towers that will accommodate the log period antenna which we have not installed yet. The balum is build utilizing five #43 2 inch ferrites.

 

Below is the finished 40M 3 element beam.

 

 

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