Fan Loop?

Ok, guys. I always ask my antenna questions over on the other site, so I figured I'd give you guys a chance to answer one. I am planning on putting up an 80 meter loop skywire antenna. It's a full wave horizontal loop fed with 450 ohm ladderline. I got to thinking the other day that maybe I could create a loop within a loop type of antenna. The outside loop would be a full wave on 80 meters; the next loop, inside that 80m loop, would be a full wave 40 meter loop; and then the third loop would be a full wave 20 meter loop. If you look at the antenna from the top, it would look like three squares inside of each other, with a single feed point set up the way they set up fan dipoles. Are ya getting the picture? How do you think this would work?

Probably not too well. You're going to be dealing with some interesting reactances as a result of the even "resonance" multiples, and I don't think your tuner is going to effectively cancel them out especially at higher frequencies.

You could get away with just one loop, cut to accommodate the lowest frequency you plan to use.

Or is a radiation angle which changes with increasing frequency what you're after?

I just want something that is going to work and work well. I've done some research on this 80m skywire antenna, and know it's a good one, but I was wondering if modifying the design to make it into a fan loop skywire (Yes, I am making up that name just in case it turns out to be a brilliant idea that I can market and make millions on. :D) would work.

My drawing totally sucks, but this is basically what the antenna would look like. The antenna itself would be horizontal and the ladderline would be vertical.

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Originally Posted by W9PSK

I just want something that is going to work and work well. I've done some research on this 80m skywire antenna, and know it's a good one, but I was wondering if modifying the design to make it into a fan loop skywire (Yes, I am making up that name just in case it turns out to be a brilliant idea that I can market and make millions on. :D) would work.

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In a fan dipole configuration, one can get away with what you're proposing. Things change when you close the ends of the loop(s).

You could stack multiple loops in a configuration that will give you optimum takeoff angles for each desired band then use a latching relay system to connect each to your open-wire line. Bear in mind that if the circumferences of each loop differ more than a very small amount (0.5%) you're probably going to need to adjust the matching network with each loop change.

A neat way to do this would be to construct a band-tracking/memory preset circuit for each. Or use separate, independently tunable matching networks at each feedpoint.

ETA: I would make the loops horizontal and the feedline vertical. You're not going to gain anything with a multiloop, horizontal broadside array unless you make one or more of the elements parasitic and use them to focus the radiated beam.

Just use it multi-band with a tuner. Make it as big and as high as you can. Trust me.

I miss my 460' loop, the dipole is OK, but the loop was quieter. The DX lobes kicked ass on 20, 17 and 15. Mine was suspended by 6 pulleys, and I could slide the whole loop to change the feed point and tweak the direction of the lobes. All it took was listening to specific DX pileups with the speaker on the roof, and I slid it back and forth. Ended up being fed about 1/4 of the length of a side closer to a corner.

One thing you can do is open one side opposite the feed point, and make it tune better on lower frequencies. This will change the pattern though...

Have you registered (free) at http://www.cebik.com

This you must do, find the Tales and Technical section, then read his stuff on loops. Well, everything, actually. :yes:

Specifically, these topics... links require login!

Notes on All-Band Use of Horizontal-Plane Loops(10-28-1997)
A 40-Meter Star (04-13-2003)
Horizontally Oriented, Horizontally Polarized Large Wire Loop Antennas (03-29-1999)
Horizontal Loops: How Big? How High? What Shape? (10-21-2004)
Half-Wavelength Interrupted Loops: Their Evolution and Uses (03-01-2008 ) (pdf)


Note: Antennex.com owns this stuff now, as W4RNL is an SK.
So all rights reserved blah blah, and you will get some spam for
expensive goodies from Antennex.com. Worth it though.

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Originally Posted by N8YX

You could get away with just one loop, cut to accommodate the lowest frequency you plan to use.

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This would be my suggestion.

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Or is a radiation angle which changes with increasing frequency what you're after?

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He'll get it, whether he wants it or not.

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Originally Posted by KJ3N

He'll get it, whether he wants it or not.

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Right, but stacking the loops and selecting one based on frequency used and height above ground will mitigate this somewhat.

You'd light up the shack like a christmas tree with rf, And cancel each other out.

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Originally Posted by N8YX

Right, but stacking the loops and selecting one based on frequency used and height above ground will mitigate this somewhat.

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If you want nothing but NVIS, sure.

I prefer a different path. ;)

The multi loops with a common feed should act just like dipoles do, except with higher impedances at resonance. IOW, the reactances will go up when the particular loops aren't resonant.

Now, as to parasitic radiators, it is the spacing that would mess up that idea, since different wavelength spacings would be necessary for each loop.

Here's a thought. How about an all-band "loop screwdriver?" Four support points being long springs with pulleys on each. Route the loop wire through the pulleys around to a small bi-directional winch at the feedpoint. The winch would pull in or pay out wire, thus shrinking or expanding the loop. Insulators added to keep the loop floating.

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Originally Posted by W6EM

The multi loops with a common feed should act just like dipoles do, except with higher impedances at resonance. IOW, the reactances will go up when the particular loops aren't resonant.

Now, as to parasitic radiators, it is the spacing that would mess up that idea, since different wavelength spacings would be necessary for each loop.

Here's a thought. How about an all-band "loop screwdriver?" Four support points being long springs with pulleys on each. Route the loop wire through the pulleys around to a small bi-directional winch at the feedpoint. The winch would pull in or pay out wire, thus shrinking or expanding the loop. Insulators added to keep the loop floating.

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Hmmmm. From a mechanical standpoint, that would require the springs to be just the right length and have just the right tension. Otherwise, there would either be too much pull or not enough pull. Also, wouldn't I end up creating a coil that would alter the antenna's characteristics when it wound up the wire for the higher bands? It sounds too complicated to figure out for a guy like me.

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Originally Posted by W9PSK

Hmmmm. From a mechanical standpoint, that would require the springs to be just the right length and have just the right tension. Otherwise, there would either be too much pull or not enough pull.

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Well, sagging and taughtness would need some adjustment. Perhaps surgical tube instead of the springs. That stuff is quite elastic and can be cut to adjust the tension so as to be just enough when on the lower frequencies and real tight when on the higher bands.

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Also, wouldn't I end up creating a coil that would alter the antenna's characteristics when it wound up the wire for the higher bands? It sounds too complicated to figure out for a guy like me.

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The coiled-up wire feed point would be where you attach one leg of the feed, so the effects of coiled up wire would be negligible. And, you'd have to run bare wire for it to work with a sliding contact point.

Nah, not too difficult, but a lot of work and ingenuity. Try the concentric multiloop idea you had. It should work like a fan dipole as those loop impedances will change as the paralleled, fan dipole ones do. Just would be a problem with parasitic elements due to the different wavelengths requiring different spacings band to band.

I'm exhausted at the moment but I'll toss this in for consideration: Carpet Loop Antenna [click]

Feed with ladder- or window-line. Adapt the switch-tapped coil idea with heavier-gauge wire for transmitting; use relay(s) at the feedpoint. You'd have to twiddle with a tuner, but you should be able to put a signal on the air in much of the spectrum. ;)