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Author Topic: Horizontal loop question  (Read 2727 times)
AF5C
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Posts: 123




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« on: February 21, 2013, 11:28:54 AM »

I remember seeing an article in QST back in the 80s where I first learned about the horizontal loop antenna for HF.  Since then, I have seen many people discuss them or say they use them, and both hams and QST say they are good DX antennas.  However, I have never seen it mentioned as to the required height above ground to be a good DX antena.  So, how high (in terms of wavelengths) does a horizontal loop need to be to function as a good antenna for DX?

John AF5CC
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WB6BYU
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Posts: 13253




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« Reply #1 on: February 21, 2013, 11:38:40 AM »

How good is "good"?

Vertical angle of radiation depends on height above ground just as it
does for a dipole.  Well, close, anyway:  the loop has an overhead null
when it is an even number of wavelengths, which tends to put a bit
more power into the lower angles.  But, in general, more height is
better.

I've worked DX on 40m and up with an 80m loop about 20' off the
ground (very irregular) but it will be much easier when it is up at
least 1/2 wavelength on the frequency you are using.  It also works
best when the loop is 2 or more wavelengths around.
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W5WSS
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Posts: 1728




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« Reply #2 on: February 21, 2013, 11:49:36 AM »

The loop shape does not preclude the antenna from horizontal oriented horizontal radiating antennas from height rules.

All horizontal antenna family members relative to height above ground will develop a pattern inclusive of the earth surface distance below. !/2 wave above ground is a good goal.

The horizontal loop perimeter can be made to cause the antenna to radiate off of the perimeter wire about the shape.
Avoid the full wave and harmonic lengths where the H loop radiates broadside straight up and down rather than off the perimeter to assure lower manifested power TOA from any height.

Or conversely make the antenna full wave and install lower for closer sky wave work.
I really would not want a 90 degree toa on the higher hf bands and certainly is possible with low full wave h loops.
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LA1BRA
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Posts: 51




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« Reply #3 on: February 21, 2013, 03:43:53 PM »

I put up my first and only loop here in Mexico as I had the real estate to do so. I like it. I run a tall trap dipole at my station in Texas and it works well too on 75 meters. center point of trap dipole is 50 feet.
My loop here in Mexico is more or less 35 feet on all four corners.
I am heard well into the US from Texas and either coast, conditions permitting....
The ARRL article suggest 40 feet at minimum for best take off angle....
Higher is better for long distance, low mounting pretty good for short NVIS as stated..
Now after all said and done, I like my loop, when I get back to Texas, I will install two more towers and position my loop at 40 feet on all four corners. It works.
I do feed mine with a 1:1 balun and coax as I only use it on 75 meters. Many comments have been posted on the virtures of feeding with ladder line, both ways work. DX eng states if you are using a tuner and the lop is far away from resoance, they have a specila balun just for multi band loops with a tuner...they also have a downloadable info package on correct balun selection per application, worth reading.
I have a tuner here also, I can tune my loop to work most anywhere, but an A to B comparison with a tuned dipole, the tuned dpole is 3 db better (on 17meters)

Good luck with your project
gd dx
73 de xe3/kb5vwz/la1bra
tom
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WB6BYU
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Posts: 13253




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« Reply #4 on: February 21, 2013, 04:18:07 PM »

The radiation pattern needs to be considered, too.  I used a 80m loop
on Field Day for a couple years and did a careful analysis of the patterns.
For a square (or "diamond") loop fed at one corner, maximum radiation is
off the corners on 40, 20 and 15m, with nulls off the sides.  On 10m it
breaks into 8 narrow lobes.  On 15m and especially 10m the narrow
pattern becomes a problem for Field Day, even from here in Oregon
where the main lobes are fairly well aligned with the population centers.

Fed in the middle of a side rather than at a corner causes more lobes
and nulls.

Any comparison between a dipole and a large loop needs to consider
the relative radiation pattern of each, as well as the heights.  In lots
of directions the dipole may be better, while the loop will be better
along the main lobes if they are at the same height.  If you have a
limited total mast height, using it all to put an inverted vee up high
would be better for DX than splitting it into 3 or 4 shorter masts for
the loop.  But if you can get all of the loop up as high as the dipole,
it will have several dB gain in the favored directions (and nulls in
others.)

It isn't a simple comparison, and "works well for DX" should be
qualified as "can work better than a dipole in some directions and
worse in others".
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W3HKK
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Posts: 596




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« Reply #5 on: February 21, 2013, 04:58:14 PM »

In the 2013 CQWW 160 meter CW Contest:

100 watts  to a one wavelength  horizontal loop at 61 ft (( 0.117 wavenlengths high)  produced 851 qsos  in all continental US states + Hawaii and 15 other countries + 39 Canadian contacts
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NH7O
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Posts: 126


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« Reply #6 on: February 21, 2013, 06:03:24 PM »

The only way to really know what is going on with horizontal loop antenna is to model your specific design, on all the bands you are interested in. I see people continue to be interested in trying these, but I have never heard what that attraction is.

There is *no* particular advantage to the horizontal loop. They don't necessarily work well, even though anecdotal stories are common enough. If someone puts in a lot of effort erecting an antenna, and proceeds to make contacts, it "works great". I have worked a station in New England who was running 10W to a stealth wire out the window of his condo, on 160m. Every dog has his day. Without A-B testing, you can never be sure.

From my experience running models of these, you can end up with a decent pattern on one band, a cloud warmer on a higher band, and lots of random sharp nulls on another band, as noted by others.

One rule of thumb that I often use, was given by W4RNL. "Tall and small is better than long and low". A lot of wire close to the ground on the low bands just ends up with more ground loss. If you work the low bands, a vertical will be a better choice.

Smaller and more effective antennas can be had for the higher bands, such as vertically oriented loops. So give it some thought, and definitely test the models first.
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AJ4WC
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Posts: 47




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« Reply #7 on: February 21, 2013, 06:05:59 PM »

In the 2013 CQWW 160 meter CW Contest: 100 watts  to a one wavelength  horizontal loop at 61 ft (( 0.117 wavenlengths high)  produced 851 qsos  in all continental US states + Hawaii and 15 other countries + 39 Canadian contacts

Excellent...  I managed to get all 50 states and 70 countries on an OCF dipole at 18ft, which theoretically should be a cloud warmer and worm burner.  

I have an 80M loop at 40ft.  It's been my experience that it performs better on the higher bands than the conventional wisdom would indicate.  Doing A/B comparisons with a vertical, I find the almost no difference between the two antennas.  With all the hype about take off angle, I think it's sometimes forgotten that antennas radiate some power in ALL DIRECTIONS even though they may obviously have gain and lobes that favor certain directions.  
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W5DXP
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« Reply #8 on: February 22, 2013, 05:10:50 AM »

I have an 80M loop at 40ft.  It's been my experience that it performs better on the higher bands than the conventional wisdom would indicate.

EZNEC says it has 10 dBi max gain at 23 deg TOA on 20m, about 3 dB higher than a 1/2WL 20m dipole, and 11.5 dBi at 13 deg on 10m.
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73, Cecil, www.w5dxp.com
The purpose of an antenna tuner is to increase the current through the radiation resistance at the antenna to the maximum available magnitude resulting in a radiated power of I2(RRAD) from the antenna.
W5WSS
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Posts: 1728




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« Reply #9 on: February 22, 2013, 07:39:28 AM »

Yes that is all true Cecil. AND When installed high enough, and when the loop is Not a 1 wave length version. for the version made to radiate off the perimeter edge as opposed to broadside. There is power manifested where the lobes are formed and very low power manifested where the nulls are formed around the compass.

I like the H loop but there exists as many nulls as lobes manifest about the entire compass of Omni directionality half is lobes and half is nulls. The Front or forward most point at which to choose to direct the most power is opposite across the way from the feed point. Lobes nulls lobes nulls etc. whether this is problematic is dependent on the operator goals and an understanding of the coverage.

When the 1 wave length loop is chosen and purposely installed low the loop can exhibit a slight amount of more gain than a h dipole also at the same height at high angles towards the zenith.

The H loop shapes tend to squish the patterns depending on the placement of feeding.

The antenna certainly offers a multi band utility with the use of balanced line and a tuner

High or low height above ground is a major player relative to the pursuits of the user.
Radiation favoring the edge and higher heights makes this antenna almost Omni directional and the lobes contain high manifested powers.

There is a height where the dipole takes dominance at all angles and a rotate able dipole is more reliable to point.
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W5LZ
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Posts: 477




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« Reply #10 on: February 22, 2013, 07:26:37 PM »

What's the best height for yours?  As high as you can get it.  You aren't limited to the 'classical' shapes either (square/circle/triangle).  The end shape can be irregular to a large extent, and that's what's going to make a big difference in it's radiation pattern.  No two installations are ever going to be exactly alike so why expect the results to be consistent?
There's no such thing as a 'DX' antenna.  All of them will 'do' 'DX' to some extent, nor are the so-called 'DX' antennas limited just to 'DX', they'll hear 'local' stuff too.
 - Paul
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AD5ZC
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Posts: 72




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« Reply #11 on: February 25, 2013, 06:50:51 AM »

I saw someone mention Cebik and here is what I gathered from reading his research on hohpl's,
the loop, when used on the higher bands as a multiband antenna, will have a lower angle of radiation than a multiband dipole at the same height and the lobes exhibited by the loop, while still there, are not as sharp as the dipole.
Now, it's not much better but it is still measurably better.
Only you can decide if the performance justifies the increased complexity of the additional supports.
Where a loop shines is in how much easier it is to match compared to the all band doublet. (when using even multiples.  A multiple that ends in .5 will be very difficult to match)

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WA9CFK
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Posts: 87




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« Reply #12 on: February 25, 2013, 09:18:39 AM »

My 80 meter loop is 45 feet tall because that was as high as I could get it.  So it is really more of a squashed diamond.  Wink

I feed it at the top with 400 ohm twin lead and use it on all frequencies except 160m.

Its biggest advantage is it is quiet compared to other antennas and it certainly is inexpensive.

It is anybody's guess what the radiation pattern looks like but it works for me.
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AJ4WC
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Posts: 47




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« Reply #13 on: February 27, 2013, 02:10:25 PM »

I have an 80M loop at 40ft.  It's been my experience that it performs better on the higher bands than the conventional wisdom would indicate.

EZNEC says it has 10 dBi max gain at 23 deg TOA on 20m, about 3 dB higher than a 1/2WL 20m dipole, and 11.5 dBi at 13 deg on 10m.

Very interesting... thanks!
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