Discussion in 'Antennas, Feedlines, Towers & Rotors' started by G5TM, Mar 21, 2019.
A sleeve balun for 40m would be 33ft long. Just use a ferrite choke.
Where my half square is located, I am more comfortable running power to it than a dipole. The foliage is near the high current low impedance points, and away from the high impedance ends.
I do run dipoles in two other directions, but North/South I am limited by the 70 ft frontage of the subdivision.
It's an "upside down sleeve balun" and is the aluminum tubing support and one of the radiating elements of the half-square. Please see the graphic in posting #32. Here is a graphic with the currents shown at the feedpoint. Is there any current flowing on the outside of the coax braid and/or the inside of the aluminum tubing?
I did do a comparison of the half square at the same height as my dipole and the dipole was still better, not by much, but certainly enough not to go through the exercise to make one. I'm still not saying it's not something to use if your ground conditions warrant it.
My point is generally that a pattern of low angle radiation is not always the whole story, total gain must be factored into the equation when deciding on antennas. If you think the difference in the low half square vs. the dipole is bad, you should see what comparing a 1/4WL vertical looks like. It too has a low angle radiation pattern.
I've been modeling a modified 40m half-square with a maximum height of 20 ft and compared it to a 40m dipole at 20 ft. The dipole radiates most of its power at high angles and would be a good NVIS local antenna. The modified half-square beats the dipole at any elevation angle below 30 degrees and beats the 40m 1/4WL vertical at any elevation. Of course, that is in the half-square's favored direction.
If you can only put up a 20' antenna for 40M a half square may be your best bet. Not my issue, however.
I've been modeling a 20 ft high 40m half-square by bending the elements horizontal at the bottom. Removing the horizontal bottom wires resonates the antenna on 20m. I'm in the process of building it and will try it out on 20m sometime tomorrow and on 40m tomorrow night.