The answer before the algebra
The wire itself is rarely the major source of loss in a full-size HF antenna. Copper or copper-clad wire has small ohmic resistance compared with the radiation resistance of a reasonably installed half-wave antenna. The practical loss budget more often appears in the feed system: coax operated at high SWR, a transformer with core or winding loss, a tuner, or unintended current on the outside of the coax shield. This article therefore ranks systems, rather than pretending that a particular length of wire can be evaluated in isolation.
With good-quality coax, ordinary attenuation is lower, but mismatch loss has not disappeared. High SWR creates voltage and current maxima on the line; those maxima raise conductor and dielectric loss. Open-wire and window line have much lower attenuation and are usually tolerant of high standing-wave ratio, which is why the balanced-line-fed doublet wins the broad multiband efficiency contest.
What actually determines the result
| Variable | Why it matters | Field consequence |
|---|---|---|
| Electrical height | Height above ground changes feed impedance and vertical radiation angle. | A wire that is low on 80 m may behave mainly as a high-angle regional radiator, regardless of its name. |
| Feed-line type and length | Every line transforms impedance; coax loss rises with SWR. | Measure at both ends of a coax run before deciding that the antenna itself is at fault. |
| Current balance | Unequal feed currents or shield current can distort the intended pattern. | RF in the shack, touch-sensitive SWR, and changing pattern are reasons to investigate the choke. |
| Coax route and choke location | In an End Fed OCF, a defined section of the coax shield is intentionally part of the antenna. | Changing the coax length, route, or choke position changes the radiating system; measure it in its final configuration. |
| Nearby conductors | Metal, wet trees, gutters, wiring, and siding couple to the antenna and balanced line. | Dimensions calculated in free space are only a starting point; trim after installation. |
System ranking for efficiency and use
| Rank | System | Best use | Reason |
|---|---|---|---|
| 1 | Doublet with balanced line | Broad HF multiband | Low-loss balanced line carries high SWR far better than coax, leaving the tuner to make the final match. |
| 2 | Resonant center-fed dipole | One band | Near-resonant impedance, low mismatch loss in coax, simple pattern, and straightforward current choking. |
| 3 | Fan dipole | Several planned bands | Each resonant element can provide a low-SWR coax match near its design band. |
| 4 | ZS6BKW | Coax-friendly fixed multiband compromise | Its dimensions were chosen to make several bands land in useful impedance regions. |
| 5 | Off-center-fed dipole | Selected harmonic bands | Can present manageable impedances, but its feed-point asymmetry raises the importance of current balancing. |
| 6 | G5RV | Tuner-assisted multiband | Useful balanced system, but a long coax section after an imperfect transformation can waste power. |
| 7 | End Fed OCF | Multiband operation from one convenient feed location | Its electrical feed point is off center, but a defined coax return section and choke location are inseparable from the antenna design. |
| 8 | End-fed half-wave | One support or difficult routing | Mechanically excellent; electrically dependent on transformer quality, insulation, return path, and choke strategy. |
Doublet with balanced line
A doublet is a center-fed, two-wire antenna whose transmission line remains part of the multiband system. The feed-point impedance may swing widely by band, but 450- to 600-ohm balanced line can transport that impedance with much less incremental loss than coax. The best implementation takes the line to a balanced tuner, or to a deliberately engineered balanced-to-unbalanced transition near the tuner.
Balanced line deserves physical respect. Keep it away from conductive objects and wet vegetation, avoid sharp bends, and maintain spacing between conductors. A short coax connection to a 1:1 current balun may be appropriate at a transition. Treating a 4:1 UNUN as the universal answer is not.
ZS6BKW and G5RV systems
Both are doublet-family systems with a matching-line section. The original G5RV uses a roughly 102-foot top and a 34-foot open-wire section intended as a transformer for particular operating conditions. It is useful with a capable tuner, but it is not inherently a 50-ohm all-band antenna. On bands where the matching section does not land near a useful impedance, coax placed after that section can be operating at high SWR.
The ZS6BKW changes top-wire and matching-section dimensions to obtain friendlier impedance regions on several popular bands. It does not create gain from arithmetic; it changes the match landscape. Its advantage is most real when the actual line type, velocity factor, height, and layout closely follow the design intent.
Resonant dipole and fan dipole
A resonant center-fed dipole is the reference antenna because it puts two equal legs around a current-rich feed point. A 1:1 current balun or choke keeps the outside of the coax from becoming a third leg. When cut and installed for one band, its low SWR makes a good coax feed very efficient and predictable.
A fan dipole joins two or more resonant dipoles at one feed point. Each element is adjusted in the final installed geometry because mutual coupling shifts resonance. The reward is low loss and easy operation on selected bands; the cost is more wire, spreaders, and iteration. It is usually a better way to cover a known group of bands than forcing one random wire to satisfy every frequency.
End-fed half-wave
An EFHW is fed at the end of a half-wave, where voltage is large and feed-point impedance is commonly in the kilohm range. The typical 49:1 transformer, insulation, counterpoise or coax return path, and common-mode choke are therefore not accessories. They are parts of the antenna system. A good EFHW can be efficient and exceptionally easy to fit into a property, but a poor transformer or uncontrolled shield current can trade convenience for heat, RF feedback, and a pattern no one modeled.
End Fed OCF
An End Fed OCF—end-fed off-center-fed—places the matching box and the radio connection at one physical end, but makes the electrical feed point off center. The long wire is one side of the system; a deliberately selected section of the outer coax conductor supplies the short second side. It is therefore neither a conventional end-fed half-wave nor a conventional 4:1-balun OCF dipole: the installation has the physical convenience of an end-fed wire, while the electrical feed point is shifted away from the extreme end-of-half-wave impedance.
The shift can produce a more moderate impedance transformation than the several-kilohm end of an EFHW, which makes this configuration attractive for multiband, one-tree, fence-line, and portable installations. The central engineering fact is that the coax route is part of the antenna. The choke defines how much shield is allowed to participate; its position, the coax length and routing, the matching network, wire dimensions, installation height, and nearby conductors must be treated as one measured system. Move the coax or choke and you have changed the antenna, not merely tidied the feed line.
For diagrams and a more introductory explanation, see the earlier post: End Fed OCF and EFHW for Beginners.
Off-center-fed dipole
An OCF dipole is still a dipole in physical form, but it is fed away from center to obtain a useful impedance on selected harmonic bands. Many practical designs use a 4:1 current balun. A separate effective coax choke is still prudent because the offset feed makes equal antenna-leg currents less automatic. “Works without a tuner” should be treated as a measurement claim for a particular design at a particular installed height, not as a law of nature.
Measurement procedure
- Measure complex impedance and SWR at the feed point, then again at the radio end of the feed line.
- Compare coax loss and mismatch loss with the actual cable length, frequency, and measured SWR rather than a generic chart.
- Measure after final installation. Antenna height, supports, slope, and nearby conductors change resonance.
- Validate the choke using common-mode current measurement where possible. An SWR-only test does not fully prove current balance.
- Record the configuration. A notebook entry with wire length, height, line type, line length, and weather is more useful than a memory of “it worked great.”
Technical references
American Radio Relay League, The ARRL Antenna Book for Radio Communications, 24th edition, 2019, especially its dipole, multiband-HF, transmission-line, balun, and measurement sections. Radio Society of Great Britain, Successful Wire Antennas, 2012. Louis Varney, G5RV, “A Multi-Band Antenna System,” RSGB Bulletin, July 1958. L. B. Cebik, W4RNL, The G5RV Antenna System Re-Visited, Parts 1–3. J. D. Kraus and R. J. Marhefka, Antennas For All Applications, 3rd edition, 2002, for dipole current distribution, radiation resistance, and feed-system principles.