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Author Topic: 20 meter inverted V dipole, anything better?  (Read 4132 times)
Guest

« on: April 25, 2002, 03:38:12 PM »

Is there an inverted V dipole antenna that works better than the G5RV antenna for 20 meters? I have also thought of the Delta loop type of antenna for 20 meters and how does that compare to the G5RV for 20 meters?  Thanks for any replys.  Bill
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AC5E
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« Reply #1 on: April 25, 2002, 04:53:40 PM »

HI Bill: It's no big secret that I don't care for the G5RV. It's touted as an all band wonder and it is not. On 160, and 75/80 it's about like the antenna that's packed in the box with an HT. A leaky dummy load.

But in my experience Louis Varney's compromise antenna is about the best simple 20 Meter antenna you can stuff into 105 feet,

PROVIDED.....

You can hang it high enough. High enough to hang the "matching section" straight down and clear the ground by enough not to hang on people or vehicles.

You can hang it flat. Essentially a G5RV works best if it's fairly flat. You cannot let the ends sag and get all it can do out of it.

You can hang it straight. It does not work well bent in the middle, and any bend anywhere will degrade performance.

You can hang it sideways from the direction you want to work. You aren't going to have great performance off the ends.

And last but far from least - convince yourself that it's a simple wire antenna with simple antenna performance, not a 6L monoband yagi.

73  Pete Allen  AC5E

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WB2WIK
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« Reply #2 on: April 25, 2002, 05:04:36 PM »

The advantage of an inverted vee, or even an ordinary 1/2-wave dipole, over a G5RV is that it can be made rotatable so you can use it to favor two directions and null out others.  This is a huge advantage of a 20m inverted vee or dipole, provided you can make it out of materials that will self-support, and place it on a mast over a rotator.  A G5RV is too large to rotate.

Given the choice of having a dozen G5RV's hanging in my yard (for 20 meters), or a single, rotatable dipole or vee...the choice is very clear and in favor of the rotatable dipole or vee.

If you cannot possibly install anything rotatable and must use a wire antenna that is not noticeable, take a look at the "One Stealthy Delta" article in May 2002 QST, on page 47.  Brilliant idea that is guaranteed to work better than any G5RV on the planet, occupies almost no room and can be made invisible!

WB2WIK/6
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WF0H
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« Reply #3 on: April 25, 2002, 05:57:03 PM »

After a flurry of recent articles in QST, I've started experimenting with loop antennas again, and I think that loops have a lot going for them.

You have lots of options for loops. Full-wave loops work at all harmonics, so a loop for 40 meters will also work at 20, 15, and 10.  With a tuner, the loop can be made to work at any frequency higher than its design frequency and somewhat lower, too. Open wire feeders might be a better choice if you are going to use the loop on non-resonant frequencies due to the losses in coax cable when the SWR is high.

Loops are inherently quieter than dipole-type antennas. When installed as a 'sloper', they can exhibit considerable gain in the direction of the slope.

My 40 meter loop is roughly in the shape of an equilateral triangle, with about 45 feet of wire on a side. The feedpoint is up on my tower at 30 feet - the higher, the better. The other corners of the loop are on poles about 10 feet above the back fence. This produces a gentle slope to the west.  

The result is a quiet antenna that hears everything well and appears to get out well, too.

You could also make your loop for 20 meters, which should work on 20, 10, and probably 6 meters. A loop can be made rotatable, too.  

There are also designs out there for shortened loops that will fit in a small space - called 'Maltese Quads'.  

Last month's QST has two articles on loops. One advocates using a loop cut for 5Mhz with open wire feeders and a special tuner to cover all bands.

There's another article in either the current QST or WorldRadio (not sure which) that describes a loop 40 feet on a side hung vertically inside a tree with an SGC Autotuner at the feedpoint to overcome the issue of coax loss on non-resonant frequencies. Neat!

Good luck!

de K0RGR
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WR6J
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« Reply #4 on: April 25, 2002, 06:35:49 PM »

While it's not the holy grail of antennas (since there is none) the G5RV is not at all bad.  Here are some practical observations:

It doesn't need to be up at least 30' to work effectively.  I have mine at only 20' flat and have the 31' of twin feedline going down 10' then out along a gutter for 12' (perpendicular to the antenna) and then down another 9' or so.  It doesn't seem to affect the radiation pattern that much - and my EZNEC model confirms that the difference isn't huge.  As I understand it, this matching section is not a radiator except when you use it on 160m where the ends are shorted and the whole antenna changes from a doublet to a marconi antenna.  In all other cases it serves the purpose of accommodating some of the standing waves at the expense of adding some unwanted impedence that needs matching with a tuner.

Specifically I have worked over 60 countries on this G5RV in the last two and a half months from my QTH in San Jose, CA.  I am using 100W and have had no problem working all around the world on all bands 10-20m.  I rarely seem to miss out on DX even in a reasonable sized pileup - as long as I am patient.  It hears fairly well.  In addition I have worked Australia, New Zealand, South Cook Is., Hawaii, Alaska, Canada, East Coast US on 40m as well as Venezuela on 80m.  All this is SSB at 100W.  On 160m I have managed to make contacts to New Mexico.  Being able to do all of this with only one fixed antenna makes it a useful choice in my opinion.

I have tried a simple 20m wire half wave dipole and in side by side comparisons with other stations it seems no better or worse than the G5RV.  I have built a 20m half square and also used 20m vertical dipoles and none of them outperformed the G5RV.  I built a quarter wave 40m vertical with quarter wave radials and it seemed to be worse than the G5RV.

I am sure if I had the ability to rotate a beam then I could do much better - but I don't, and for a fixed multiband antenna the G5RV seems to do a good job.

Just my opinion,

Richard
WR6J
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« Reply #5 on: April 25, 2002, 09:42:19 PM »

Thanks for your thoughts on this and I must say that I agree with everyone here. Like Pete says, I hate the G5RV because of the layout and configuration of it's matching system with 31' of ladderline and 90' of coax to the rig, but then as Richard says it does get you to the far away places.  I also have a G5RV installed and have worked most of Europe and South America, the far East and Austrailia but I would like to try something better even a little better would be nice. The article's on loops and delta loops in QST lately have been about what I'm looking for but I'm not sure if they top the G5RV.  Thanks again guys!  Bill
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WA4PTZ
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« Reply #6 on: April 26, 2002, 04:12:56 AM »

Yes,  A 20 meter coaxial dipole.
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« Reply #7 on: April 26, 2002, 12:08:32 PM »

Thanks Tim for the idea on the coaxial antenna. I have seen info. on it some place but I can't seem to find it now. Do you or anyone else have any information on it?  I'll continue looking through my books and see it I can find out about it.  The thought enters my mind though if it's hard to find out about it then maybe it's not too hot of an antenna. Bill
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WR6J
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« Reply #8 on: April 26, 2002, 12:54:30 PM »

In this thread you'll see a posting on the coax dipole.  I am going to try one over the weekend if I get the time.  However, it is not claimed to work any better than a regular dipole - it's main advantage is that it is end fed.

http://www.eham.net/forums/Elmers/19420

Richard
WR6J
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Guest

« Reply #9 on: April 26, 2002, 01:48:07 PM »

Good information Richard but I'm looking for probably what you would call a double bazooka antenna. I'm trying to improve what I have for 20 meters which is a G5RV. I'm not interested in the other bands, just 20 meters.  The G5RV is a pretty good antenna on 20 meters, but I'm looking for something better if at all possible in an inverted V configuration. I think all I need now is a performance rating on the double bazooka antenna.  Bill
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WB2WIK
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« Reply #10 on: April 26, 2002, 01:56:11 PM »

The double bazooka coaxial dipole is mostly hype.  I've built dozens of these and the only noted difference compared with an ordinary wire dipole made of #12 or #14 gauge copper is slightly improved bandwidth.  On 160 meters, even a small BW improvement (theoretically about 13% improvement is possible) may be worthwhile, since most antennas are so very narrowband.

The problem with the double bazooka is protecting the junctions where the dipole is fed (you feed the outer shields of a piece of coaxial cable having its shield connection, but not its center conductor, cut in the middle) -- this is a weak point that must be mechanically reinforced to get any life out of the antenna.

I've found that simply making a 1/2-wave dipole out of "fat conductors," such as using 450 Ohm ladder line as the radiating element, offers the same bandwidth improvement without the frailty of using coaxial cable, and at somewhat lower resultant weight.  Much has been recently documented on this subject, in QST and QEX magazines.

WB2WIK/6
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WR6J
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« Reply #11 on: April 26, 2002, 02:22:59 PM »

OK - so you may want to look at phased antennas to increase gain.  One possibility on 20m would be a phased extended double zepp.  This would be two double zepps in parallel (about 8' apart if I remember right) and fed with a phasing line.  There is a design for one in one of the ARRL wire antenna books.  I could give you a reference when I get home.

On the other hand Steve probably has the whole thing memorized!

Richard
WR6J
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NB6Z
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WWW

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« Reply #12 on: April 26, 2002, 04:31:32 PM »

Bill,
If you are mainly interrested in 20 meters, look into a 20 Meter EDZep wire. You can find details and specs for two shortenned versions of a 20 meter Zepp wire at:
http://home.teleport.com/~nb6z/nb6zep.htm
Easier to build and feed than a G5RV... They make good all band wire antennas if you know where to expect the RF fields to radiate the best on each band. Like any horizontal wire, the higher the better.
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RobertKoernerExAE7G
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« Reply #13 on: April 26, 2002, 09:32:57 PM »

What isn't your present antenna doing?

What do you want a new antenna to do better than your present one?
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KF4ZGZ
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« Reply #14 on: April 28, 2002, 03:21:29 PM »

Since all you want it for is 20m, go with the lowly dipole. It's simple, easy, and if fed with coax, will tune the whole band without a tuner ( no extra loss ).
And , it's small enuff to go with the earlier post of making it rotatable.

Good Luck and 73 de Matt, kf4zgz

"The best antenna is the one you build yourself!"
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