|Antenna 010: Horizonal End Fed Vee
Author: Frederick R. Vobbe, W8HDU
August 7, 2008
A Horizonal End Fed Inverted Monoband Vee is a lot like the standard End Fed Vee, with the exception that the ends are raised to the same height as the center support. So insead of it being an inverted Vee, it's more like a Vee laying flat on the ground then elevated.
In Figure 1 we see a typical Horizonal End Fed Inverted Monoband Vee. Note that the ground portion of the feed point is 1/4 wave, while the "hot" side is multiple 1/4 wavelengths or 3/4 wavelength in our illustration.
Since the ends are now up, the pattern of the antenna smooths out considerablty over a traditional End Fed Vee.
If we look at it from the top in figure 3, we can see that the radiation pattern is like a dipole, except the it's slightly flatend and spread out. Still, there is 7.25 dB gain, making this antenna very useful. The take-off angle is 60 degrees which could be a factor in some cases. And the antenna impedance approaches 110-j90. This may be unsuitable, but before discarding this design, read on.
Figure 4 shows another perspective of gain and nulls in the antenna. Again, you note that there is not a sharp lobe of radiation off the side of the wire as you would get in a traditional dipole.
The antenna I designed had a measured impedance of 111.9 -j81.35. My Yaesu FT-857D would not load into it, so I had to use the Drake MN-75 to get the VSWR under control. As it turns out, the MN-75 has a laddar line output which was perfect for feeding the antenna. Below, in figure 5, is the VSWR plot on 7.1500 MHz if you assumed feeding it with 50 ohm cable.
What does the VSWR look like with 110 ohm laddar line? Much better! As you can see in figure 6, the VSWR is down to nil at our operating frequency, and pretty darn good across most of 40 meters.
To make this easy get about 150 feet of wire. Cut off 144 feet of #12 wire (assuming that we're building for the 40 meter band). Why 144? Because our antenna will be roughly 136.657 feet full wave (for 40 meters) and we'll need to wind the end of the wire around some insulators. When we are done we can "tweak" the antenna by shortening the wire at the ground end by a few inches. The other 6 feet will be used to support the antenna at the ground ends, (gray closest to ground), and for jumpers. Cut one piece of wire to 36 feet. The second piece would be 108 feet. The rest of the wire is used for supporting the antenna
Construction is much the same as the End Fed Vee. You will need four insulators. Unless you are running extreme power, you can use plastic "egg" insulators. If you are running over 500 watts of power I would use the glass or porcelain insulators. If you need the plastic insulators, I have them for sale. I would appreciate your business!
Take each piece of wire and attach them to an insulator. If you are using insulated wire, you can wind the wire with insulation through the insulator. However, we will need to bare at least 2" of the end. Make sure that your wire does not slip through the insulator. Personally, I use Belden 8000, or I have used #10 THHN. But I'll remove some of the insulation an wind the loose end around section goint to the insulator and put some solder on it to keep it from slipping.
Add about 6" of wire at the feed point to attach to your coax or balun. After you install the coax or balun be sure to seal the wires attaching to, and the exposed dielectric of the coax with RTV or Silicone caulk. You don't want water ingressing into your coax.
Frederick R. Vobbe, W8HDU
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