Hams in general, and traveling hams are always on a quest to find the "ultimate" portable antenna Of course there is no single skywire that fills every ham's needs, but there *is* one type that comes very close and is somewhat forgotten. What I'm talking about is a classic historical aerial, the End-Fed Half-Wave Antenna, Zepp or Fuchs antenne. Known since the early days of radio. I found a description of the Zepp in QST 1928! It is extremely simple to erect and use. In spite of its simplicity the HyEndFed has the benefit of giving repeatable, efficient and effective performance.
Many antennas used for portable operation suffer from lack of effectiveness. That is, they don't produce the number of QSOs expected, as compared to operation from a home location. Most of the time this stems from the fact that the antennas used when going portable are intentionally simple, and because of this they don't put you few watts of where they belong.
One type of "simple" antenna used for portable operation is the vertical antenna. If used with a good ground system a quarter-wave vertical antenna can be very effective. But often portable use dictates an antenna that is not a full quarter wavelength long and a ground system that is far from optimum. Consider two things:
1) According to the ARRL Antenna Book, a quarter wave vertical antenna with fifteen 1/4 wave ground radials may have an efficiency of only 50%; with fewer radials the efficiency suffers even more.
2) Efficiencies of short mobile whip antennas listed in the same reference are often only 10% or so - and that is with a car body as a ground plane. With a poorer ground it is even worse! Unless you have a full-size vertical antenna with an extensive ground system you are converting most of your transmitter power to heat, not tickling the ionosphere.
Another popular portable-use antenna is the random length wire and tuner combination. If properly implemented this antenna can be very good. Unfortunately it can be hard to tell just what "proper" means. If the antenna is shorter than a quarter wavelength, it suffers from the same efficiency problems as the vertical antenna. Further, unless you choose the length correctly, the radiating part of the antenna may be at your operating position, wasting power radiating into ground-level surroundings, rather than being up in the air squirting out RF where it belongs. Because of the unknown nature of its impedance, the random length wire antenna needs a tuner capable of matching over a wide range of impedances.
One of the best choices for portable operation is the center-fed half-wave dipole antenna. It has the benefit of being very effective and not too difficult to properly erect. On the down side, it does require end supports at the right spacing and height. You need to contend with a heavy feedline at the center which has to be brought away from the dipole at right angles or performance will be degraded. Multiband operation is possible but the best way to do this with a dipole requires an open-wire feedline and a relatively complicated symmetrical tuner.
If you take a half-wave dipole, eliminate the feedline and feed it directly at the end, you have an antenna that has many of the advantages of the dipole with few of the limitations of other portable antenna methods. This antenna has been described for years in the ARRL Antenna Book and other amateur radio publications but it has received little attention lately.
Without the feedline the antenna is a snap to put up. Freed of the restrictions of the center feedline, the HyEndFed fits into situations that would be difficult for the dipole to handle. When erected well of the ground and clear of surrounding objects, it is as efficient as the dipole and it is effective because radiation from it is predictable so that the signal goes where you want it to go. No tuner, just hook up the coax and go.
Also, because it is only a single wire with a insulator and a little matchbox integrated in the second insulator the HyEndFed is lightweight and small so it is easy to store and transport - things to consider for portable use. It doesn't have to support a center feedline so physical strength is not an issue. A temporary portable telescoping fishing rod antenna mast can be used..
The total overall length of the HyEndFed is an electrical half-wavelength, calculated from the formula L (Ft) = 468/F(MHz) where L is the overall wire length in feet and F is the desired operating frequency in Megahertz.