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The Very Simplest Homemade Hi Q Loop!

from Jeff Brone, WB2JNA on February 2, 2018
View comments about this article!

The Very Simplest Homemade Hi Q Loop!
By Jeff Brone, WB2JNA

Hereís a limited space stealth antenna that is so easy to make and costs so little you might not even think it will work, but I assure you that it can. Itís a Hi Q loop. You can make it mostly with things you have around your house or apartment. You will need:

A hula hoop (you probably can get one at a thrift shop if you have to, but even if you buy one itís a small cost)

Aluminum foil

Two old pill bottles. One needs to slide into the other. Not the smallest ones, but not too big either

A length of insulated wire, roughly one fifth the length of the hoop

A few pieces of scrap wire and some wide clear tape.

Wrap strips of aluminum foil around all but two inches of the hoop. Try to do two layers of foil. On the side of the hoop opposite the bare two inches attach the insulated wire (only mechanically, not electrically) with a few pieces of tape so it forms a loop as indicated in the picture.

You will attach the coax (center and braid) to the ends of this smaller loop.

Make your tuning capacitor out of the pill bottles. Wrap the smaller one with a few layers of aluminum foil strips, then one layer of clear plastic tape to insulate the foil. This will slide into the other bottle which will be lined on the inside with strips of foil. Attach a wire to the foil on each bottle (tape it, slide it under the foil, etc. whatever works best for you). Attach your wire leads to each ďsideĒ of the foil where the bare two inches of hoop show. Try to keep the leads short (maybe shorter than mine!).

This method worked best when I made this homemade variable capacitor. You may try a different design. If youíre having trouble getting the antenna to resonate, add a 6-12 inch long piece of coax to the capacitor terminals (braid to one side, center to the other). This will add some capacitance. Then retune the variable capacitor.

Prop the hoop upright (or place it on a chair or on a non-conducting pole) and attach an SWR analyzer, noise bridge, etc. to the opposite end of the coax attached to the smaller loop, and adjust the capacitor (slide the inner bottle in and out) for the best SWR. You will have to experiment with the capacitor, the shape of the smaller loop and the position of the antenna so be ready to do that. It may take some fiddling, but eventually you will find a match and can then attach your rig to the antenna and make some contacts. The RF energy is coupled inductively to the larger loop through the smaller loop. A few things to remember:

DONĒT TOUCH THE ANTENNA WHILE TRANSMITTING! You could get a burn.

Iíd only put about 5-10 watts into the hoop. It isnít made for high power. And donít sit too close to the loop (to minimize RF exposure). If there is any arcing in the capacitor, stop transmitting.

You may have to adjust the capacitor sometimes, and readjust the capacitor every 20 kc or so if you move frequency.

This antenna is definitely for use under a roof, not out in the elements for an extended time!

Using CW and even some SSB I have used loops like these to talk to stations on four different continents. This particular one worked Europe and North and South America just today. It resonated best on 20 meters and seemed also to work on 17 meters. Those bands are good places to start with your loop. Also it is so low cost and simple itís a great conversation piece. As always, use caution and be careful when building and transmitting. Good luck!

Member Comments:
Add A Comment
 
The Very Simplest Homemade Hi Q Loop! Reply
by N3HKN on February 2, 2018 Mail this to a friend!
I built one out of copper tubing but with a piece of 9913 coax as a capacitor. I just trimmed it until I had resonance in the 20 meter band. Then I set it outside on the deck. It WORKED. That is, until I wanted to find what 100 watts would do. Well the end of the coax capacitor, dangling from the top of the loop. exploded in a beautiful blue arc of considerable brightness.

Later, replacing the coax with a real large variable capacitor, allowed me to use the loop all summer but when winter came the cheap little motor froze. I scrapped it.
Dick N3HKN
 
The Very Simplest Homemade Hi Q Loop! Reply
by N2FQ on February 2, 2018 Mail this to a friend!
Excellent. I use a aluminum bicycle rim. Thanks for the article.

Fernando N2FQ/6
 
RE: The Very Simplest Homemade Hi Q Loop! Reply
by AI4WC on February 2, 2018 Mail this to a friend!
BRAVO! This article clearly demonstrates a radio amateur's application of the principles involved with antenna design. Never mind that it may appear to be a child's worthless junk; it is an art form and an electrical marvel that needs only refinement in the place of "Make Do." I love it and I encourage more of us to not be afraid to "make do!" THIS is what we are all about!
 
The Very Simplest Homemade Hi Q Loop! Reply
by AF7EC on February 2, 2018 Mail this to a friend!
Nice! Thanks for the article!

Those medicine bottles *do* come in handy, don't they? :-)
 
RE: The Very Simplest Homemade Hi Q Loop! Reply
by WB2JNA on February 2, 2018 Mail this to a friend!
Thanks for all the positive responses. I'd love to see more of us get into making things out of simple raw materials.
 
RE: The Very Simplest Homemade Hi Q Loop! Reply
by WB2JNA on February 2, 2018 Mail this to a friend!
Thanks for all the positive responses. I'd love to see more of us get into making things out of simple raw materials.
 
The Very Simplest Homemade Hi Q Loop! Reply
by OZ8AGB on February 3, 2018 Mail this to a friend!
Cola cans can also be used as a capatitor:
http://www.alexloop.com/artigo36.html
 
The Very Simplest Homemade Hi Q Loop! Reply
by W8LV on February 3, 2018 Mail this to a friend!

Great Article!

Have you tried to tune this without an Antenna Analyzer, by listening for Maximum Noise on receive?

73 and All the Best!
DE W8LV Bill


 
RE: The Very Simplest Homemade Hi Q Loop! Reply
by WB2JNA on February 3, 2018 Mail this to a friend!
Yes and that can work as well.
 
The Very Simplest Homemade Hi Q Loop! Reply
by W0FAA on February 3, 2018 Mail this to a friend!
Since you didn't specify, I'll clarify that you will likely get the best efficiency if you unroll enough foil to equal the circumference of the loop, then wrap it the "long (difficult) way" around the loop. This will provide a continuous conductor with lowest resistance. One tenth of an ohm of series resistance can destroy the efficiency of a loop like this and some people might be tempted to pass the roll of foil through and around the support like winding a coil. That would result in a coil with the windings shorted by the overlapping foil portions and unknown additional distributed inductance and resistance.

Sure it will work (poorly) even if poorly built, but a loop like this can be made 90% efficient, so why not try to optimize it a bit?

 
RE: The Very Simplest Homemade Hi Q Loop! Reply
by W8LV on February 4, 2018 Mail this to a friend!
Just out of curiosity,
what was the farad value range
of your variable Prescription
Bottle Capacitor?

If you make the big loop out
of say RG-213 instead,do
you short shield and
conductor together, or do you
just ignore that?

Thinking a lot about other
ways to make the variable
capacitor from homemade
expedient materials...

Like all "Radio Kids",I made a fixed capacitor
as a kid out of sheets of aluminum foil and a book.

Placing sheets of he foil in the book,
using the pages of the book for
imsulators... rolled up the foil ends
that protruded from both sides
of said book, placed crock clips on
these collectively rolled up ends... Charged that up and got just a little tiny
spark when I shorted them together.
Used a larger book to make a FrankenCap,
but still only got a small spark.

I'm sure there must be lots of ways
make that variable cap, and even hang
a little homemade fixed cap across
to get it closer resonance.

73 and All the Best!
DE W8LV Bill
 
RE: The Very Simplest Homemade Hi Q Loop! Reply
by W8LV on February 4, 2018 Mail this to a friend!
Just out of curiosity,
what was the farad value range
of your variable Prescription
Bottle Capacitor?

If you make the big loop out
of say RG-213 instead,do
you short shield and
conductor together, or do you
just ignore that?

Thinking a lot about other
ways to make the variable
capacitor from homemade
expedient materials...

Like all "Radio Kids",I made a fixed capacitor
as a kid out of sheets of aluminum foil and a book.

Placing sheets of he foil in the book,
using the pages of the book for
imsulators... rolled up the foil ends
that protruded from both sides
of said book, placed crock clips on
these collectively rolled up ends... Charged that up and got just a little tiny
spark when I shorted them together.
Used a larger book to make a FrankenCap,
but still only got a small spark.

I'm sure there must be lots of ways
make that variable cap, and even hang
a little homemade fixed cap across
to get it closer resonance.

73 and All the Best!
DE W8LV Bill
 
RE: The Very Simplest Homemade Hi Q Loop! Reply
by WB2JNA on February 4, 2018 Mail this to a friend!
Good questions.
I don't know what the range of the capacitor is. Good enough to work I guess! It would be interesting to know but I don't have an easy way to check it, I don't believe.
You can short out the braid and center of a coax loop, or just use the braid. I'd try both ways and see what works best.
Good comment above also on the wrapping method of the foil. Sounds like sound advice.
Thanks!
 
The Very Simplest Homemade Hi Q Loop! Reply
by KD9BYI on February 10, 2018 Mail this to a friend!
Looks like a fun project.

I use a mfj loop tuner and 1/4 inch copper pipe. I think even a large wire works ok if you make your loop closer to a 1/4 wave.

Shouldn't that be much better than the commercial 3 foot loops?
 
RE: The Very Simplest Homemade Hi Q Loop! Reply
by WB2JNA on February 11, 2018 Mail this to a friend!
I think it should be pretty good in any case, and allows you to experiment with different configurations if you want, which is a bonus!
 
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