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1-10 of 15 messages
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Best wire antenna for 40 meters?
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by K9MAN on August 29, 2001
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What wire antenna will have the best performance on 40 meters, a dipole, a G5RV or a Carolina Windom? Or what wire have you found that works the best?
Thanks, Joe
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RE: Best wire antenna for 40 meters?
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Anonymous post on August 29, 2001
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Is the antenna primarily for DX chasing at night, or daytime local work?
How big is your yard?
What kind of supports (natural or man-made) do you have, and what are the relative positions of the natural supports?
How high can you get the antenna?
Do you want gain in specific directions at the cost of having less signal in other directions?
Do you have much man-made QRN at your location?
What's the ground conductivity like in your area?
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RE: Best wire antenna for 40 meters?
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by WB2WIK on August 29, 2001
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It surely does depend on what you're trying to do with that wire...
...a low doublet, whether it be a dipole, a G5RV or a Windom type (off center fed dipole, or OCFD), will work quite well "locally," within a few hundred miles.
That same antenna (whichever it is) substantially elevated, say, 65' above ground or higher, will start to become an effective "DX" antenna, good for worldwide contacts at night, but will do so at a slight loss in "local" effectiveness.
That same antenna oriented vertically (center fed vertical dipole), which of course might be quite a trick with a 66' long doublet, will have an even lower radiation angle and become an even more effective "DX" antenna, at the considerable sacrifice of local effectiveness. In fact, I use a vertical on 40m most of the time and work into Africa better than I can locally -- but that's a fact of life with vertical antennas.
A 1/2-wave, resonant (by definition) dipole can be fed with coaxial cable and no antenna tuner, and should match up quite well and require no tuning. A G5RV (102' doublet fed with a matching section of ladder line spliced to coaxial cable 30' below the antenna) is non-resonant on 40m and almost always requires a tuner. The OCFD, or at least the "Carolina Windom" sold by RadioWorks, is 66' long and seems like it should be resonant, just fed in a funny place. I have no idea why this would be more effective than an ordinary center fed, resonant dipole. A real "Windom" antenna has no center insulator and is not fed with coax...the original design was an off-center fed horizontal wire, tapped 1/3 from one end (dimensionally), and fed with a single wire to form a top-loaded Marconi that had both vertical and horizontal properties. I understand the basis for that design; I do not understand the basis for an off-center fed dipole having unequal length legs and a coaxial transmission line. Maybe that's just me!
For a given aperture, any number of antenna designs will work about the same way, with the major variable being the installation (height above earth, orientation, etc). I can take a 66' long center-fed dipole and make it a super DX antenna (by installing it vertically), or a great "local work" antenna (by installing it low, and horizontally), or most anything between.
73 de Steve WB2WIK/6
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RE: Best wire antenna for 40 meters?
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by AC5E on August 29, 2001
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HI Joe: First, either the off center fed dipole that we commonly call a Windom or a center fed dipole will do you a nice job on 40 at the typical (low) heights most of us get to hang antennas.
The OCF dipole is really a multiband antenna that does not give much away on bands above the band it is cut for. The feedpoint is chosen to give a reasonably low SWR using 50 ohm line on the fundamental and the harmonics, something a center fed dipole lacks. As far as fundamental frequency performance is concerned, it's just another dipole.
The center fed dipole has a reasonable SWR on the fundamental frequency and the ODD harmonics, so a 40 meter dipole works pretty well on 15 but not at all well on 20 or 10. In fact, if it weren't for transmission line losses most "wide range" tuners could not "tune" a dipole on its even harmonics.
The "full size" G5RV is touted as an all band wonder, and the truth is that it works fairly well on 40 and up provided you have a wide range antenna tuner and you are willing to put up with the coax losses. On 160 and 80/75 the G5RV is about like the antennas that come packed with HT's. Leaky dummy loads but better than nothing.
And if DXing is your game - go with a vertical and either a good radial field or an elevated radial field. You will be much happier. But don't neglect the radials or you will be really unhappy with the results.
73 Pete Allen AC5E
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RE: Best wire antenna for 40 meters?
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by K9MAN on August 29, 2001
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Thanks for the responses.
The use will be local/state side not DX.
The wire will not be vertical.
Height will be a max of 40'.
Length a max of 132'.
Can use the built-in antenna tuner in my IC-746 if needed.
The main question is, will any other wire type antenna out perform the dipole given the above constraints?
Thanks, Joe
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RE: Best wire antenna for 40 meters?
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by WB2WIK on August 29, 2001
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132' is certainly "too long" for a 40m dipole, which will work best when cut to 468/f = length in feet.
Making the dipole longer will do little or nothing to enhance its performance, and in many cases it will be seriously worse with regard to loading it up and undesirable lobes and nulls. Surely, you want to avoid the "full-wave center fed" problem, which is one where the antenna is nearly impossible to load because its feedpoint impedance is way too high to match with anything. That problem would occur at about 132' in length.
The only suggestion I can offer for a wire antenna 40' high that might fit in your available space and offer results typically superior to a dipole is a full-wavelength horizontal loop. This only requires 33' per side for a square loop (and square is easy to deal with, usually), and loops tend to work quite well even when fairly low, like 40 feet. Feed it with ladder line (450 Ohms) or twin lead (300 Ohms), using the BALANCED terminals of a good outboard antenna tuner (_not_ the coaxial tuner built into the Icom!) and you'd have a winning antenna that will not only work very well on 40m, but will work quite well on several other bands. Although these do develop multiple lobes on the higher bands, they remain quite "omnidirectional" in nature because of the four sides.
(Note: A loop need not be square, it's just a convenient way to discuss one. It can have 3-4-5-6-n sides, and obviously as you approach an infinite number of sides, it becomes a circle. But performance is usually best, and most predictable, when all sides are the same length.)
73 de Steve WB2WIK/6
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RE: Best wire antenna for 40 meters?
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by NB6Z on August 29, 2001
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To answer your question... Any of those wire antennas, if at the same height above ground, will perform about the same on 40 meters. They generally get their "gain" at frequencies above 40 meters, so a dipole might be the easiest to construct for 40 meters only. If you plan to operate 20 meters and above as well, you can do better than a simple 40 meter dipole. Those other antennas will have gain above 40 meters, but they also will have nulls. A forty meter doublet becomes a 20 meter double zepp antenna and is usable on other bands as well.
Here are the details for a all-band wire antenna that will fit in the space of a 40 meter dipole:
http://www.teleport.com/~nb6z/nb6zep.htm and one that is a modified 40 meter meter doublet:
http://www.teleport.com/~nb6z/nb6zepJr.htm
Have fun... Griff
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RE: Best wire antenna for 40 meters?
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by AC5E on August 29, 2001
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HI again Joe. To answer your question about wire antenna "performance," the sad fact is that 100 watts in gets you no more than 100 watts out. A beam antenna focusses that 100 watts in one direction, while a resonant dipole of any sort hung a half wave or more up concentrates its radiation in a "half wheel" pattern perpendicular to the wire.
As a practical matter, the only difference between a dipole and some fancier skywire is the degree of concentration. IF you want to put a better signal into HA and your supports will allow it a really directional antenna may be just the ticket. But for general use, without favoring any particular direction, it is hard to beat a dipole of one sort or another.
And yes, a multiband skywire does get "lobey" on the higher bands. But that is not necessarily bad.
Unless they have repealed the law of physics since I went to school, each lobe is actually a cone! That is, if the lobes of a long wire stick out on the sides like an ice cream cone, the actual three dimensional radiation pattern is much like a half section of that cone.
The pattern starts low on one side, goes over the top, and ends low on the other. So if you have a wire exactly north and south, you may have low angle radiation toward Europe and NZ, higher angle radiation toward the poles, and low angles again toward the South Atlantic and Siberia. And that ain't bad.
But regardless of all the hype, and remembering that everyone's bird dog and pet antenna is the best in the world and nothing else is worth considering, I 'spect an OCF dipole cut for the lowest band you intend to work would get the job done about as well as it can be done.
73 Pete Allen AC5E
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RE: Best wire antenna for 40 meters?
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by RobertKoernerExAE7G on August 30, 2001
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"The use will be local/state side not DX.
Height will be a max of 40'."
I think I would put up either an inverted Vee, fed with coax, or a delta loop fed at either bottom corner with 75 ohm cable.
Shud be enough to have tons of fun state side on 40.
For DX, feed the delta 1/4 wave from the top (per ON4UN).
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RE: Best wire antenna for 40 meters?
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by AC5E on August 30, 2001
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Yep, a delta loop will also do an excellent job. So will an inverted Vee. Will they give greater field strength than a dipole at say, 20 wavelengths from the radiator? The delta will, a little, in some directions. And less in others. The inverted vee is pretty much a wash.
In every case, 100 watts to the feedline, less feedline loss, less ground loss, less element loss, is all the radiation you get with any antenna. Any performance difference is in how it's concentrated and how much or how little noise it picks up.
Dipoles of any sort are pretty simple to hang, fairly easy to keep up, reasonably quiet, and they are usually high enough in the air so there is no danger someone will get an RF burn or a broken neck from one. With all the starving shysters among us, those are important considerations.
But of course, everybody to their own taste, as the goodman said that kissed the pig.
73 everyone Pete Allen AC5E
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