TheRadioBoard

Saw an article about loop antennas that said they used a hula hoop.

My question is can the wire be scramble wound or does it have to be separated and/or close wound?

SWsenior

If you think of the loop as an inductor, it doesn't matter how you get the inductance, as long as you can resonate it. You'll get less self-capacitance (which means more tuning range with a given variable capacitor, as the minimum circuit C is less) and greater Q by spreading out the turns. The small commercial tunable loops like Kaitos and Terks must have close-spaced turns, yet they work pretty well (I have a Terk). People have made high-L loops on quilting hoops, but the turns on all of these loops are probably side-by-side, not scrambled. The disadvantages of scrambling in a hula hoop may be offset by its larger diameter. You may not need the Q or tuning range and may benefit by better nulling. Only way to know how well it will work for you is to build and test. Let us know!

73,

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http://kr1s.kearman.com/
http://qrp.kearman.com/

Thanks Jim,

I'll give it try. ( Now if the guy up the street still has that hoop!)

I have seen the one you made. I have tried to find a 24" hoop at some of the fabric stores and hobby stores, but no luck.

I found a site that has a calculator for hoops: others may have already used it.

Http://www.angelfire.com/mb/amandx/loop.html

SWsenior

I was looking for a hula hoop to support a single-turn loop I wanted to try, and never could find one. I guess that fad has passed.

Some online sellers carry quilting hoops, but because of the size the shipping could be high. They don't weigh much, though. I had to put weights under the base to keep it from tipping over when I reached up to turn it. I got my hoop at a Jo-Ann Fabric. The base came from a Michael's. Neither store carried both, but fortunately they are close together here. I think you'd have to cement two quilting hoops together to get enough width for a MW loop, as they aren't very wide.

Going to 23" isn't absolutely necessary; a smaller-diameter loop would still work well, if that's the only size quilting/embroidery hoop you can find. The Kaito and Terk loops are only 14" or so. One of the inventors of the chip used in the Tecsun PL-380 made a Hoop Loop only 6" in diameter and seemed happy with it, but he's not a hard-core DXer. I made one that size, but didn't feel it nulled as well as the bigger one.

73,

_________________

http://kr1s.kearman.com/
http://qrp.kearman.com/

After reading this, I mozied over to the infamous great auction site to see if anyone is selling hula hoops. There are tons of hoops there. Most are decorated and fit together in sections for dance and workout.

But a couple of vendors are selling plain children's hoola hoops in sizes up to 36" diameter.

Okay, I went and looked. At those prices I'd consider small PVC and a hair dryer! The glitzy colors would sure get the neighbors wondering, though.

73.

_________________

http://kr1s.kearman.com/
http://qrp.kearman.com/

Visit your local heating and air conditioning contractor and scrounge a length of PEX in-floor heating tubing. It has an ID of about 5/8" and could be bent into a loop 24" in diameter or more. Think of it as a custom hula hoop!

73, J.B., VE3EAR

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To be where I am, I had to leave where I was!

dezzertrat: Nice price but the shipping?? nah I'll pass

KR1S: I need not disturb the neighborhood! I have to make a trip to the big city next week and I will check out the stores you mentioned, Jo-Ann Fabric and Michael's.

J.B.: I looked at the pex at the local Ace hdwe, only problem was the fittings to attach the ends is very expensive. The guy there showed it to me and bent it in a circle! I might consider that though, IF the brass fittings will not interfere with the coil.

Then again, I just might construct it out of wood or pvc pipe as it would be much easier to do and less hassle for me.

Thanks

SWsenior

I used 5/8 diam irrigation tubing. It's common and cheap out here as lots of folks have drip irrigation systems.

You can probably use a short length of wood dowel to make the joint (glued).

I got a quilting hoop at Beverly's Fabrics for about $4.

Have also used 10 conductor ribbon cable to make my inductor. It's a small pain to solder the ends together in staggered fashion, but when you're done, you have a nice flat inductor that can be taped to the hoop body.

Rich

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Homebrew Radio ex-Silicon Valley

XtalHWJ,

Now I will check out you idea.

Thanks

SWsenior.

I just tried a loop with Vanguard PEX (from Lowes). ID is just under .500", and a slightly sanded hardwood dowel fits fine. I may try using an outdoor covered plastic electrical box for a base, passing the tubing ends thru opposite sides and securing them with ty-wraps or nylon screws.
Thanks for the idea of PEX.
Mike AD1OS

Well, I got a 5' length of Pex and used a 1/2" cpvc coupling to connect the ends. I will tell you, it was hard to feed the wire around. I have 12 wires (22 ga) in the loop. It really isn't that good, but it does null out a station fairly well. I am thinking that I will attempt a smaller size, as this loop is about 20" in diameter. Wife picked up 2 14" hoops at a yard sale today, and I might try that to see if it will be better than the bigger loop. (it should be much easier to wind a wire on!)

SWsenior

I found this site http://www.angelfire.com/mb/amandx/loop.html and am wondering about something. Does the wire size make any difference?
I was told by someone here that it would, but can't remember for sure! ( I know, I'm old! )

SWsenior

I feel your pain! A loop antenna is an inductor. As with any inductor, due to skin effect (rf tends to travel near the surface of a conductor), which effectively increases the conductor's resistance, Q increases with wire diameter. This would be more important on a crystal set than a superhet with good IF filters. Depending on how much tension you put on the wire as you wind it (assuming a frame loop), thicker wire won't stretch as much. Larger wire looks more impressive too. I used 24-gauge on the Hoop Loop but I wasn't very concerned about antenna Q, as the radios I use it with have good internal filtering.

73,

_________________

http://kr1s.kearman.com/
http://qrp.kearman.com/

SWsenior -- here's my 2 cents.

I think the wire size matters in 2 ways --

a.) The larger the wire, the less the resistance, the larger the Q, the sharper the tuning. BUT, if you're using magnet wire, I'll bet you won't see much difference.

b.) The larger the wire, the wider the "winding spacing" is in the calculator. The "winding spacing" is the total width of the windings, including the space between windings. Try the calculator with the 8 turn example. Make the "winding spacing", say, 0.4". Then do it again with say 0.5" -- which might correspond to using bigger wire. The inductance goes down quite a bit. So HERE the wire size matters.

Note that the calculator spits out the inductance in nanohenries. Divide by 1000 to get microhenries. (191,000 nH = 191 uH).

Good luck.

73, Dan