Unusual dipole configuration?
Hi all, thanks for reading. I'd like to hang a dipole on my property, suspended between trees as I don't have a large lot. I've pondered a G5RV dipole for 80-10 meters but I'd love to get 160 meters, too. I could have room for a 160-meter dipole if I hung the feedpoint from one tree and suspended the ends from two other trees but here is my problem: hanging the feedpoint from one tree and the ends from two other trees makes it into sort of a "laying down letter V" with an angle of about 40 degrees (feedpoint at the "tip/point/base" of the V), and read as I try, I don't know how this will affect the antenna's performance. Does anyone have any ideas? Thanks!
Yeah. That's just called a horizontal V antenna.
Anything works but I wouldn't do this; it becomes directional (with some gain) in the direction of the opening of the vee, and more so as you increase the operating frequency so the legs become longer than a wavelength.
Could be pretty useful in one direction, but this usually isn't the goal.
Some people use G5RVs (standard 102' version) on 160m by simply shorting out the feedline at the rig end (literally short circuit the center conductor and outer conductor of the coax, using a shorting adapter with a single wire connection) and feeding the whole mess as if it were a single-wire antenna. (To make this work, the coax outer conductor cannot be grounded, such as by a lightning arrestor in the coax just outside the shack wall.) With a good ground system (such as wire radials on or just under the soil, connected to the ground post of the antenna tuner and not to the coax shield), this becomes a top-loaded Marconi. If the feedline is long and mostly vertical (and not running all through the house!) it can be an effective antenna when fed this way for 160; then you remove the short and just feed it in the conventional manner for the higher bands. A G5RV needs a tuner, anyway.
All sorts of stuff works, but a horizontal vee with a 40 degree opening wouldn't be my choice unless I wanted a unidirectional vee-beam for the higher bands.
The closer you make the ends of the dipole, the lower the feedpoint impedance, and the lower the gain. To give you an idea, for a 160 meter dipole, if the legs were 45 degrees apart, and antenna at 30 ft, the feedpoint impedance would be about 12 ohms. The gain on 160 would be down about 3 dB from a flat top dipole at the same height. If you used the antenna on the higher bands (30 meters and up), the max gain would be in a direction bisecting the angle of the wires.
Wow, this info is hugely helpful. I think I'll skip 160 meters for now. I'll probably go with a standard G5RV and external tuner with my TS-440's internal tuner, too. One more question, if I may: would it do any harm to run balanced, 450-ohm ladder line all the way to my tuner's balun (MFJ 941E) rather than switching to coax 30 feet from the feedpoint as most of the G5RV plans recommend? Thanks again.
No, it will probably work better.
Originally Posted by KD7EKG
I talked to a guy in Illinois that had a 160 meter dipole that he was going to put up at the property that he was living at. He moved to town. And he said that he got tired of seeing it in a drawer and decided to put it up. he was in a regular place in town with a garage in the back by the alley. He said that he strung the feed point up the peak of his rafters, and ran one end to the garage, to a tree, back to his house again and to another tree. The other end he ran it to his garage, to a tree on the other side of his house, back to his house, back to his garage, (PHEW!!) I mean this looked like a spider web. Anyway it eneded to his 6' fence.
Like I said I was talking to him at the time and he was 20 over. Him and a friend of his just got done stringing this thing up and I was the first lperson he was talking to on it on 40 meters. I asked him what other antenna he was on before this one, and he said a G5RV. I asked him if he could switch to that and see what the difference would be. He switched to it and he was only a 9. He switched back to his zig zag antenna and he went back to a 20 over. By this time there was about 8 other people on the frequency saying the same thing. That he did way better on the 160 meter antenna.
But I don't know how it did on 160 meters, but it worked as good as a beam on 40.
There is nothing magical about a G5RV. Somehow it's become the antenna everyone thinks works well on all bands. It doesn't. It's great for 20 meters.
Cut your dipole for 1/2 wavelength on 80 meters using the formula 468/(freq. in mHz), which on 80 meters ends up being around 125 - 130 feet depending on your frequency. Feed it with the same 450 ohm line to a tuner and it will work better than the G5RV on 80 and give you the other bands as well, using a tuner.