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Author Topic: Ideas for a 80 + 160 meter Antenna  (Read 962 times)
W1DY
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Posts: 29




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« on: September 28, 2003, 07:42:07 PM »

Right now, I am using an Alpha Delta DX-EE..and having a LOT of SUCCESS with it!
It is covering 10-40 no problem for me...
Although 40 doesn't tune SWR as low as I'd like even with my Ameritron ATR-15 tuner...

Anyway...

I need something for 80...160 would be nice also..but the length requirements that I've seen prohibit installing in my yard...

Length is my main concern.....I just don't have a lot to work with...

Any one leg can't be more than @60 feet... (unless it can straddle my roof.)

I looked at the Alpha Delta DX-B..but it seems useless without a yagi or the like to act as a capacitor hat.

I'm looking at the DX-A. now..but I don't want to narrow my choices yet.

Thanks
73
Wendy
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KB0ETC
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Posts: 248




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« Reply #1 on: September 28, 2003, 08:57:54 PM »

Try a horizontal loop.  For 80 meters (3.8Mhz)it is 264' long, installed in a square it is only about 60' per leg.


Feed with ladder line and a balun.  Best DX antenna I have worked from a wire.


Will tune from 160-??? what ever your outboard tuner can handle.

I tune a full wave 160 meter loop, about 600' long and covers everything in the spectrum I may want to chase.
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W1DY
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Posts: 29




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« Reply #2 on: September 28, 2003, 09:23:53 PM »

Horizontal loop....

Now you do mean running the wire parallel to the ground correct?

How high off the ground does it need to be?

Do you have a diagram...or a link to a "How To Build" plan?

If I lay this out I can give it to my Husband to build and install when he get's his next "Honey Do" list!

W1DY
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KB0ETC
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Posts: 248




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« Reply #3 on: September 29, 2003, 06:00:56 AM »

Here is a good place to start:
http://www.bloomington.in.us/~wh2t/loop.html

Here are some pictures to help you visualize:
http://www.radioworks.com/nloop.html

The loop antenna has a long and distinguished history, but is often overlooked in light of the current focus on dipoles. However, loops do have some rather significant advantages over a dipole. Since the design of a loop is typically a circle or square form, the need for a long straight run of wire used by a dipole is diminished. A loop is quite forgiving, and perfect symmetry is not essential. It is necessary only to hang it in the configuration providing the greatest enclosed area. As such a loop can be strung up in unusual places and still perform well. Treetop suspension is ideal, but you'll be surprised how well it works just lying on the roof where nobody sees it. Unlike a dipole that must be center fed, the loop can be feed at any point, allowing a most flexible feedline arrangement.

A loop is an efficient broadband radiator, even when low to the ground. The majority of the amateur bands are harmonically related, typically the 1st harmonic. This is where the loop really shines, as a loop is easily tuned to resonance on all harmonics of its fundamental frequency. A dipole by contrast is easily tuned to resonance only on its odd harmonics. A loop starts out with 1.2 dB of gain over a dipole on its fundamental frequency, and gains are even higher if the antenna is less than a quarter wave off the ground because that is where the dipole efficiency plummets. For example, in my location my loop is quite close to the ground, only about 30-40 feet up at the highest point. Nevertheless, the antenna both tunes, and transmits just fine.

A loop's gain over a resonant dipole increases with the increasing frequency of operation, so when used on its harmonics, a loop's signal advantage over a dipole likewise increases. For a horizontal loop, that's not the end of the good news, because as frequency rises, radiation angle drops lower and lower, producing increasing DX results that can rival a complex multi-element beam mounted on a 100-ft tower.

The venerable loop is easy for your tuner to match, even when fed with coax. The feedpoint impedance of a loop never gets as high or low as with an antenna that has free ends. Even a 40-meter loop can offer full 80- 10-meter coverage. My 160-meter loop allows me to both receive and transmit from the 160-meter band to 10 meters. Signal reception is also quite good with a loop for a number of reasons. As it is a terminated antenna, it is much less susceptible to atmospheric and man-made noise. As the majority of man-made noise is vertically polarized, the horizontal polarized loop can reduce electrostatic noise as much as 26db when compared to dipoles or verticals, so it is great for noisy RF areas.

The theoretical feedpoint impedance for a full wave loop antenna is approximately 100 ohms, but this does change, and is dependent upon antenna height above ground, near-by structures, and ground conductivity. When used with a 2:1 balun this presents a good match to the typical 50-ohm coax. Due to the low height above ground of my loop, I used a 4:1 balun which seems to offer a wider tuning range (lower Q). With the use of a transmatch (antenna tuner) I am now able to use my loop from 160 to 10 meters.

Loops can be either a 1/2 or full wavelength long. The formula for a full wave loop antenna is as follows: Length (feet) = 1005/fMHz. For example, a loop for the frequency of 3.800 MHz would be calculated as follows: 1005/3.8 = 264 feet. You can now divide 264 by 4 to obtain the length of each of the four legs of the loop. 264/4 = 66 feet each leg.

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NI0C
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Posts: 2418




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« Reply #4 on: September 29, 2003, 11:14:20 AM »

Other antennas to consider are the "inverted-L" antennas (a wire antenna that is partly vertical and partly horizontal).  If you don't have room for that you might consider the Butternut or MFJ verticals that cover 160 meters.  These antennas (including the inverted-L) require radials to reduce earth losses.  I'm using a Butternut HF-2V ground-mounted vertical that covers 160m (with the optional kit), 80m, and 40m.  Advantages are it is slim and stealthy, and fits among all the trees and other constraints on my property.  Disadvanteges are: limited power (500w.) and bandwidth (about 20Khz) on 160m, and the base loading is pretty lossy on 160m.  It works very well on 80 and 40m, however.

Good luck!  The low bands are fun!

73 de Chuck  NI0C
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WB2WIK
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Posts: 20633




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« Reply #5 on: September 29, 2003, 02:14:56 PM »

You might also check out the excellent article on shortened dipoles in the current (October 2003) issue of QST.  A half-sized dipole with properly designed and built loading devices can be built to have nearly the performance of a full-sized dipole, but in half the space.  Pull the center up as high as possible to make an inverted vee, and the horizontal space required is even smaller.

I use a loaded, half-sized inverted vee on 160m with its center up only about 51' above ground (side arm off my tower).  It occupies only about 100' horizontally, with each end about 15' above ground, and makes solid contacts on 160m, reasonably competitive with those nearby running full-sized dipoles.  A great DX antenna it isn't...but it does work DX during contests, when there's a lot out there to work.  At least it gets me on a band that otherwise would be difficult for my small lot.

WB2WIK/6
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WB6BYU
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Posts: 13461




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« Reply #6 on: September 30, 2003, 04:11:20 PM »

QST had an article on a 40/80/160m trap dipole that was
about the length of a standard 80m dipole.  I'm
guessing it was in the early `90s.  It was a bit short
on details, so further information was provided in the
Technical Correspondence column a few months later.

Sorry, I don't have my QST indices handy to look it up.
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W1DY
Member

Posts: 29




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« Reply #7 on: September 30, 2003, 11:41:04 PM »

Traps are out for me....
I need something to handle 1KW.

I guess 160 is out of the question...and really not needed to get my 5 band DXCC.

I have a G5RV...and was just thinking....
If I was to join the ends..I would have a Loop...

But it would only be 103' long....
I guess this weekend I'm going to have to measure off the entire back yard to see what the MAX total length would be...

I could feed from the mast on my house that has the DX-EE already on it...
That is as high as I can go....
Then run the corners as high as practical...

I have had ZERO luck with HomeBrews...
But every antenna I bought has worked wonders!

If this keeps up...I'm going to get an Inferiority complex!

Since I'm now concentrating on a 80 Monoband..Or a 40/ 80...
That should open up some options for me...
SO I guess the question is what is the best/Shortest 80 Meter antenna w/o traps?
What about those ISOTRON...antennas....??

Wendy
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NI0C
Member

Posts: 2418




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« Reply #8 on: October 01, 2003, 11:23:51 AM »

There are many antennas with traps that can handle 1 KW with ease.  If you are after 5 B DXCC, I think it might be slow going with a very small antenna such as the Isotron.  Again, I'd recommend a Butternut vertical, preferably elevated, or ground-mounted with as many radials as you have room for.  Some of the Butternut and Hy-Gain verticals that cover 80m are only 26 feet tall.  Anything smaller than that isn't going to be very effective on 80m.  

BTW, the 500w. limitation I mentioned concerning the HF-2V pertains only to 160m-- the antenna is designed to handle 2KW on 80m and 40m.  

GL & 73,

Chuck  NI0C
 
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N3ZKP
Member

Posts: 2008




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« Reply #9 on: October 01, 2003, 04:01:28 PM »

Wendy:

Nice name, by the way. Same as my daughter-in-law. Smiley

I have to agree about the Butternut verticals. Despite old wife's tales, they are excellent performers when properly installed. If they weren't, DXpeditions would be using them for 160-80m work.

I have an HF6V that is installed on the roof of my office building. I live at the rear of the building and have all my antennas mounted there. The Butternut is two stories in the air and is mounted in the middle of 23k square feet of corrugated steel, so you see I don't have ground plane worries. The point is, with a proper radial system, these are excellent performers and will handle more than your AL-80B (or my AL-80A) will put out - except for 160m.

Due to the low takeoff angle, it is an excellent DX antenna. I have almost 200 confirmed in four years of very casual DXing. The one good addition to my shack recently is the LDG AT-1000 auto coupler. It handles the Butternut very well, even matching it at 5-mhz for MARS use. It is a good combination with the AL-80A.

Good luck and Good DXing,

Lon

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N9NEO
Member

Posts: 93




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« Reply #10 on: November 05, 2004, 04:23:11 PM »

Steve (and others)

I would like to put up a shortened 160m antenna that you describe.  It sounds like just what I am looking for.  I will run coax to it and drive it with about 300w pep. Please give me a clue on the construction or a link that might help.

I had asked my friend to send me a copy of October 2003 issue of QST, but I am looking at it now and it is March issue.  I will ask again.  I only get QEX.

See my modulator design in NOV/DEC issue of QEX.

73
Bob
N9NEO

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