Loop Antennas

The Hidden Secrets of the Vertically Oriented Horizontally Polarized One Wavelength Loop

Written by:  Ludvick W Rummel

When you talk about antennas, I would have to say, that the most important specification of an antenna, is its radiation efficiency. The ratio of power radiated to power fed to an antenna. Of course there are many types of antenna efficiency, For example how efficiently does the antenna radiate the power in the most desirable directions or the most desirable take off angles. Ninety percent of all communication that amateur radio operators do will require takeoff angles between 10 degrees and 60 degrees and the majority of time you are communicating between 20 degrees and 45 degrees.

So it makes no difference whether, you are talking to someone 50 miles away or 12,000 miles away these are the takeoff angles you'll need. When you use, a dipole, yagi, inverted V, vertical, or even a loop antenna that is parallel to the ground the range of takeoff angles you will have, is determined by the height of the antenna above ground, but when you look at how a vertically oriented horizontally polarized one wavelength loop antenna works you realize it is different the most obvious difference is it radiates at two different heights above ground.

This is very important, and highly desirable because the two different radiation patterns overlap each other thereby reinforcing and complementing each other this is because the loop in this configuration is actually two antennas in one the best way to visualize this is to look at the antenna as an inverted V dipole, at the top of the antenna and a V shaped dipole on the bottom. The center of the V shaped dipole is the feed point of the antenna. The inverted V dipole is double end fed from the ends of the V-shaped dipole that is beneath it. These two dipoles are operating as a phased array. They are electrically 180 degrees out of phase with each other.

The distance between the two high current points is, four tenths of a wavelength, the first high current point is at the feed point and the second one is half way around from the feed point at the top of the antenna. The fact that they are electrically 180 degrees out of phase with each other and they are four tenths of a wavelength apart from each other is where the 3db gain of the antenna comes from. Who would have guessed that a single piece of wire could be so complicated. But as everyone knows a picture is worth a thousand words. Figure 1 below shows the elevation angle of a horizontal dipole at ½ wavelength above ground. Figure 2 shows the same antenna at one wavelength above the ground. Figure 3 shows the loop with the bottom of the antenna at ½ wavelength above ground and the top of the antenna at 9/10 of a wavelength above ground. As you can see from figure 3 the amplitude of your signal both on transmit and receive, does not change more than 2db from a 55 degree takeoff angle all the way down to 7 1/2 degrees so you can work short, medium, and long skip off of the Ionosphere simultaneously.

ke4uyp's Ham Radio



figures-1-2-3

 

Very interesting article !
However I was nor able to find the Figs. (1, 2, & 3)
mentioned in the article.
I have a Horizontal Loop for 80, 40, 20, 15 & 10 mts.
myself and I'm very impressed with it performance.

Thanks & 73

Juan KG4QYYjuan@wellkids.org

 

</span><table border="0" align="center" width="95%" cellpadding="3" cellspacing="1"><tr><td>Quote (KG4QYY @ July 30 2002,06:26)</td></tr><tr><td id="QUOTE">[/QUOTE]<span id='postcolor'>
</span><table border="0" align="center" width="95%" cellpadding="3" cellspacing="1"><tr><td>Quote </td></tr><tr><td id="QUOTE">I was nor able to find the Figs. (1, 2, & 3) mentioned in the article.[/QUOTE]<span id='postcolor'>

The figures are here.

Matt (k4mls)

 

I am and have been using vertically hung loops for a while now, but mine are even a bit more effecient since they are circular.

I have two circular loops mounted on one boom for 10 and 15 meters and for those who have contacted me on these bands know how well these things work.

I chose loop antennas because over the three sunspot cycles that I have been a ham , it has always been one antenna that stands out over all the rest as the simplest and best DX antenna , and its the old reliable simple and super efficient 2 element cubicle quad.

Since I do not have the tower or the bucks for a multiband 2 element quad I opt'ed for a  circular one element "quad" if you will (one wavelength) and it works very well using a tree limb as a a support and the good 'ol armstrong rotar method.

For 40 meters I use a one wavelength horizontal square loop at .2 wavelengths up (18 feet) using the ground as a true reflector, this gets out with gain (maybe 7 or 8 dB) from 30 degrees to 90 degrees up with no holes in the pattern and is so friggin' simple.

Check me out here at qrz.com for a drawing of this. 30 degrees and up it gets out like a bandit , below 30 degrees the lower angles (and the European broadcast QRM) get rolled off !

For 80 meters I am using  a near vertical sloper loop which is fed on the side for Vertical Polarization and is resonant for the DX window and favors Europe.
Feeding it on the side seem to get rid of the high angle component and associated atmosperic static and left the DX to come in, next season hope to do the same with another 80 meter sloper loop but favoring JA and Alaska.

Loops rock, they are pretty much invisible, and when they fall down you just put them up again, no $$ lost.

cheers
Jerry KC2UT
Syracuse, NY

Hey QRZ.com thanks for this e service, I no longer subscribe to any magazines because of services like this you provide.

 

Great article. I've been using a horizontal loop for a few months now, and am very impressed with the performance I've seen. With mine, I made it in the shape of a square, connected 2 corners of it to the two corners on one side of the house, then connected the remaining 2 corners to two trees next to the house. It's not exactly one wavelength on any band (in fact, I never even measured the wire), it's not really a square shape (actually, more of a trapazoid), and it's not actually even parallel to the ground (one tree was very easy to climb high in, and the other wasn't easy at all ), but this antenna is still the best I've ever used. I have no problems working both stateside hams as well as plenty of DX. An antenna tuner is a must, of course, seeing as how I didn't measure anything, but that's OK. I can get it to tune all the way down to 80 meters with the tuner built into my FT-890.

With a design that seems to work so well, with so little work and $$ involved, it's surprising that more people don't use them.

73
Dan

 

great to see the interest in loop antennas.....there is a fine book by the late joe carr, k4ipv JOE CARR'S LOOP ANTENNA HANDBOOK "your guide to large and small loop antennas for transmitting and receiving"....i have many antenna books and this is by far my favorite...joe was a great writer and his work is very easy to follow ...if you hate math, as i do, joe has tables with all the figures you need for length, matching sections etc. mine came from universal radio in ohio...likely available at amazon etc.
dan,k3xr

 

"Ninety percent of all communication that amateur radio operators do will require takeoff angles between 10 degrees and 60 degrees and the majority of time you are communicating between 20 degrees and 45 degrees. "

I do not know where you obtained those figures, but they are not supported by any research and documentation in any book I have read.  

For local communications, say 500 miles out, maybe those take off angles would be valid.  But for any distance farther than that, most take off angles are significantly lower.  A QSO from NY to Utah, which is near the extent of a single hop, take off angles probably averages around 9 degrees.

I have done extensive modeling with N6BV, the author of "All the Right Angles" which is a study of take off angles required for various communications distances.  In most cases where you want to transmit farther than your back yard, take off angles rarely exceed 30 degrees, and in most cases the majority of angles are well below 10 degrees.  

For working DX, the main goal is to lower your take off angle BELOW 10 degrees.  Most DX is worked with low take off energy.  If you have a lot of energy at 30 degrees, but the path only supports a take off angle of 4 degrees, guess what?  You will only communicate with the energy at 4 degrees.  All the energy at 30 degrees is essentially wasted.

You can see some of the results of our analysis of the 6Y2A contest operation on my k2kw.com web page, specifically at http://k2kw.com/verticals/whyvert.html  scroll down and you will see samples of the take off angles on 80m from 6Y to JA (97% of all take off angles on that path are below 10%).  There is also a 10m graph on angles from 6Y to EU (similar to the path from FL to EU), and about 95% of the take off angles are below 15%.

I also agree with others that you cannot break up a loop antenna into the upper and lower components and model it that way.  It needs to be modeled as a complete antenna.   In general, you will have MORE energy at low take off angles (below 10 degrees) with a flat top dipole at 0.9 wavelength than a loop with the top at the same height.  Yes you will get about 2 dB gain around 25-30 degree take off, but your low angle gain will suffer since much of the antenna is below the 0.9 height, which will raise the antennas response below 10 degrees take off.  

Happy modeling,

Kenny K2KW

 

I also am glad to here someone talk about take off angle. Take off angle is the main indicator of the DX capability of an antenna.

There was a reference made to the fact that it is difficult to to find and implement spreaders in loop. if you like treated wood or bamboo works well. But the easiest method is to remove the spreaders. How do you do that? Use pipe with those thingies that connect with the pipe and turn 90 degrees. Use three of the 90 degree connectors and 4 pipes and then feed it in the remaining corner and it is now a diamond loop. Anyway you will benifit from a more rugged design and less loss because your conductor is thicker.

It is true that the loop won't act like two seperate antennas as presented by the poster but it will vector out and produce a different pattern than presented. For a really low radiation throw vertical over a tree and set up a counterpoise.

Have fun

 

Very interesting article and responses. Its interesting to note that the angle decreases as the frequency increases (in an 80mtr loop,at 80 mtrs you radiate almost straight up but at 15, you have an excellent angle) I started with a 40 mtr loop up about 35 feet(it was as close to square as I could make it) It performed much better than I had anticipated on 10-20mtrs. The sensitivity on receive was much better than the dipole at 45 feet, and less noisy too. After 3 weeks, I put up an 80mtr version, and again, was very impressed with the results on 10-40mtrs. Three weeks later, I switched to balanced "window line" and it got even better! Although it is a "cloud burner" on 80mtrs (and to some extent on 40) I have had no problem working stations 400-500 miles away with my 80 watts on ssb. I have been experimenting lately with dropping one side to achieve a "sloper" and a better "angle of attack. My opinion? A great antenna for all bands if you have the room and supports. Lots to explore. Try it, you'll like it!
73's
Rick

 

Good article. Some of the comments state that a low horizontal loop if really not good for DX. I agree with that statement but this should not stop anyone from trying a low loop or dipole. My experience with a low dipole on 160 meters is ver good. In one 6 month season, I worked all 48 states and 22 countries. All confirmed with a 250 foot cloud burning dipole bent in a "Z" configuration. So, low cloud burners do work after a fashion. However, if you want real dx, stop stringing wire and do with a simple vertical. I put up a full size 80 meter vertical, 65' of aluminum and never looked back at a low dipole. Got WAS and WAC on the 80 meter vertical. Feeds directly with coax and has a low angle of radiation. Verticals rule.

K2WH

 

Can somebody help?  I've got a vertically oriented rectangular loop antenna.  It's 85' high at one corner and 100' across to the other high corner which is at 55'.  It's about 20' high on average across the bottom which is about 120' across.   So it must be roughly 360' circumference.  It's made of #10 solid copper and is fed with 450 ohm twin lead just a little bit off from the center of the bottom.  I can match it to 50 ohms from 80 thru 10 with an MFJ 989C, but it won't tune on 160.  The signal to noise ratio is remarkable.  It's the quietest antenna I've ever used, and seems to demonstrate no directional characteristics at all.  The first month I put it in operation, I worked about 70 countries.

Can somebody model this antenna in some manner and tell me what it's doing?  I'm very curious as to why it works so well.  Thanks...

 

I adapted the horizontally polarized loop antenna as a replacement for the traditional quarter wave whip in aircraft.

It only works in the tailcone of an aircraft made of composite materials (fiberglass, epoxy, styrofoam), and takes advantage of the fact that the fuselage in the tail section is made of non-conductive material.

The traditional approach had always been to embed a screen ground plane in the fuselage bottom and mount a whip in the center. But with a full-wave loop at airband frequencies, you get the benefits of lower static and noise, and a little front-to-back gain.

There is a fairly sizable group of experimental aircraft builders (including me) who have aircraft that can take advantage of this construction method. It keeps the antenna away from wings and tail, where it is common to find carbon fiber and other semi-conductive materials used as spar material.

See http://www.davemorris.com/dave/MorrisDFLoop.html for details, photos, diagrams, etc.

 

One thing that people aren't mentioning regards the S/N ratio.These antennas are definitely very quiet.I've toyed with rectangular full wave loops.Once the proportions of the rectangle are near 2:1,the feedpoint impedance is close to 50 ohms when fed from the middle of one of the smaller sides.And with an analyzer,the proportions can be tweaked to get 50 ohms,so direct feed is possible without any matching device.Bill Orr's Radio Handbook shows more about this and loops in other shapes.

 

I currently have two horizontal loops up in the back yard, one for 40 and one for 30M. The 40 M foreign bc signals are attenuated and the QRP rig gets through the noise and garbage and I can have QSO's at night!
All day when the DX signals are not there, I Can have nice rag-chewing QSO's on 30 or 40 M with just a few watts. I reach most of the eastern states and provinces of Canada. It was not so easy with the dipoles or verticals.
I also have a multiband vert plus a yagi, they get me the DX when I am in the mood for that!
Keep on loopin'
JD

 

JD has found the one big secret of a 40 mtr loop and thats bye bye foreign broadcast, but lets not spread the news and enjoy the great evening qso's, hi
There were some nice posts on this topic, see you on the NightHawks 7255.
-KC2UT