Best wire antenna for 40 meters?

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Steve Katz:
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







Griff:
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

Pete Allen:
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
 

Bob Koerner:
"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).

Pete Allen:
 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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