Parallel dipoles and balanced feeder

[N2RJ]

I want to put up a parallel dipole - 80-10m, has four elements.

However, I want to feed it with 450 ohm balanced feeder.

1, it's cheaper.

2, I have plenty of it.

3, It's lower loss than coax.

But does it make sense to put up a parallel dipole? How does it compare to a doublet? Let's just say I make an 80m dipole (doublet) and feed it with ladder line. How much am I at a disadvantage compared to:

1. Doublet (80m) with ladder line

2. Parallel dipole with coax

I'll be mostly on 20m/40m but I want to do 75/80m, and mostly DX (low angle of radiation).

[WB2WIK]

The whole reason for parallel dipoles is to make resonant, low-Z (about 50-70 Ohms) elements for each band, which accomplishes two important things:

1. Good match to coaxial cable (low VSWR), and equally if not more importantly,

2. A real dipole radiation pattern (bi-directional, two lobes only, one on each side of the dipole's broadsides) for each band.

If you make a parallel dipole and feed it with high-Z line like ladder line, you'll have a 9:1 or so VSWR on each band where the dipoles are resonant and a potential mish-mosh radiation pattern, which violates both of the original goals.

I'd either make a parallel dipole and feed it with coax, or if you like wire, have property, and don't mind using a tuner, use more wire and install a 550' perimeter horizontal loop fed with balanced line. That's a more effective antenna overall and will work every band from 160m through 10m fairly effectively, much better than any length doublet.

The reason for that last statement is simple: As a doublet becomes too long (>1 WL) it develops multiple gain lobes with deep nulls (suckouts) between them. When you get to x2, x3, x4WL long, those lobes become long and skinny and align themselves along the wires axis, and do not favor the doublet's broadsides like a true dipole. As such, unless you can somehow rotate this dipole, it can be very ineffective in many directions -- as much as it is effective in others. And the directions the lobes favor vary by band!

With a loop, pretty much the same thing happens; however, because the loop has four sides, the lobes are aimed in many more directions and the nulls between them aren't as notable. A great use for a long piece of wire!

I coined the phrase many years ago (it's been published in several periodicals), "A loop is the best use of wire since the piano." And I still believe that.

WB2WIK/6

[K0HWY]

FWIW, I'm feeding a parallel inverted vee (80/40) with 450 ohm balanced line and it seems to be working great.

[KG6YTZ]

Quote[/b] (WB2WIK @ May 07 2007,08:46)]With a loop, pretty much the same thing happens; however, because the loop has four sides, the lobes are aimed in many more directions and the nulls between them aren't as notable.

Just a thought... Suppose the loop isn't a square or a rectangle. Suppose it's closer to being circular - say, an octagon. What then?

[N4CR]

Quote[/b] (KG6YTZ @ May 08 2007,00:02)]

Quote[/b] (WB2WIK @ May 07 2007,08:46)]With a loop, pretty much the same thing happens; however, because the loop has four sides, the lobes are aimed in many more directions and the nulls between them aren't as notable.

Just a thought... Suppose the loop isn't a square or a rectangle. Suppose it's closer to being circular - say, an octagon. What then?

The more area your loop occupies, the better, so any arrangement that approaches a perfect circle is better. The more sides, the better. The higher, the better. A circle would be optimal at any given height. The problem is that you'll get more improvement from raising it up than in making it more like a circle, so a smaller number of taller supports will work better and save money.

[WB2WIK]

Quote[/b] (ai4of @ May 08 2007,00:06)]

Quote[/b] (KG6YTZ @ May 08 2007,00:02)]

Quote[/b] (WB2WIK @ May 07 2007,08:46)]With a loop, pretty much the same thing happens; however, because the loop has four sides, the lobes are aimed in many more directions and the nulls between them aren't as notable.

Just a thought... Suppose the loop isn't a square or a rectangle. Suppose it's closer to being circular - say, an octagon. What then?

The more area your loop occupies, the better, so any arrangement that approaches a perfect circle is better. The more sides, the better. The higher, the better. A circle would be optimal at any given height. The problem is that you'll get more improvement from raising it up than in making it more like a circle, so a smaller number of taller supports will work better and save money.

I agree with that.

A circle is great, but very difficult to support because it needs so many supports (for HF). (Obviously, for VHF this isn't an issue as the loop can be made of tubing and self-supporting.)

Most of us use a "square" shape because it only requires four supports.

WB2WIK/6