Behavior at beaches and over seawater with comparison to conventional inland systems
Technical report
A base-fed quarter-wave vertical at a beach is the same fundamental monopole as an inland quarter-wave vertical. Its potentially better performance comes from the electrical properties of seawater and wet salt sand, not from a different radiator. Saltwater can reduce near-base ground loss and strengthen low-angle far-field reflection. It does not eliminate the need for a controlled RF return path such as elevated radials, a ground-radial field, or a carefully engineered immersed counterpoise.
Scope and terminology
This report concerns HF and lower-frequency quarter-wave vertical antennas. The exact pattern and impedance depend on frequency, antenna height, radial geometry, soil conductivity, tide, salinity, wind, wave height, and the receiver location. The statements below distinguish measured or modeled mechanisms from installation-specific outcomes.
| Term | Meaning in this report |
|---|---|
| Quarter-wave vertical | A base-fed monopole about one-quarter wavelength long, operated against an earth return, radials, or counterpoise. |
| Local RF ground | The near-base region where return currents and fields can dissipate power in real earth or water. |
| Far-field reflection | A distant reflected component that combines with the direct radiated field and reshapes the elevation pattern. |
| Coherent reflection | Specular reflected field with a predictable phase relationship to the direct field. |
| Diffuse scattering | Randomized reflected energy caused by surface roughness, including wind-driven waves. |
How radio signals behave from a beach site
The diagrams separate effects that are often mixed together. Very close to the antenna, the concern is return-current loss. Far from the antenna, the concern is the combination of direct and reflected fields. A smooth conductive sea can produce a strong coherent reflection; a rough sea redistributes some of that energy into a diffuse, fluctuating component. In the landward direction, ordinary soil commonly has lower conductivity and can add more local loss, while its reflected field is usually weaker and more dependent on soil moisture and terrain.
Ocean direction
- Calm or electrically smooth water: the reflected field is predominantly specular and can reinforce or cancel the direct field at particular elevation angles and receiver distances.
- Rough water: wave height and slope reduce the coherent component and add diffuse scattering. The received amplitude and phase become more variable, producing multipath fading rather than a single stable reflected ray.
- At HF, the sea also supports favorable low-angle ground-wave and near-horizon propagation compared with ordinary land, subject to frequency and path geometry.
Land direction
- Ordinary soil has lower and more variable conductivity than seawater. The near-base return-current region can dissipate more power unless a generous radial system carries the current in wire.
- The landward reflected field still exists. Its amplitude and phase depend on permittivity, conductivity, moisture, terrain roughness, vegetation, and polarization, so it is less predictable than an ideal smooth-water surface.
Why saltwater helps but does not replace radials
A perfect conducting plane is a useful reference model: the ground image makes a quarter-wave monopole behave like one half of a half-wave dipole, with radiation confined to the upper hemisphere. Real seawater is highly conductive, but it is not an infinite perfect ground plane and a beach installation is not uniform seawater. The feed-point environment includes wet sand, dry sand, changing shoreline geometry, water depth, and the actual counterpoise connection. These variables can move resonance and change impedance.
A direct seawater connection may provide a low-loss path, but the installation should still be treated as a system. A conductor in the water, elevated radials, a radial field, and nearby feedline outer-surface currents can all become parts of that system. A feedline choke is therefore important when the coax shield should not become an uncontrolled additional radial.
Radial count and configuration
| System | Typical radial provision | Strength | Caution |
|---|---|---|---|
| Sparse on-ground | 2 to 4 wires | Fast and portable | Loss and pattern can be strongly site-dependent |
| Inland surface or buried field | 16 to 32 practical; 60 to 120 low-loss benchmark | Lower ground loss and repeatable performance | Uses space and wire |
| Elevated counterpoise | Four symmetric radials, tuned for the actual band and height | Return current mainly in copper; compact | Needs symmetry, physical support, and tuning |
| Beach ground mount | Use many available surface radials, or add an elevated counterpoise | Saltwater and wet sand can reduce loss | Tide and wet/dry sand change the installation |
| Seawater connection | Engineered immersed conductor plus controlled counterpoise where practical | Potentially very low local loss | Corrosion, safety, connections, tide, and water depth matter |
Measured HF work by Rudy Severns found four elevated radials performed much like 32 surface radials in the tested configurations. That is an important design guide, not a universal conversion ratio: radial height, symmetry, length, band, ground quality, and nearby conductors all matter. The traditional 120 radial system is a broadcast-industry near-perfect-ground benchmark derived from the Brown, Lewis, and Epstein work.
Comparison with a regular inland quarter wave system
| Characteristic | Beach or saltwater site | Regular inland system | Design implication |
|---|---|---|---|
| Radiator | Same quarter-wave vertical | Same quarter-wave vertical | Do not credit the wire length for the difference |
| Local loss | Potentially low over seawater or wet salt sand | Often higher over typical soil | Use radials or elevated counterpoise in both cases |
| Reflected field | Can be strong and coherent over calm sea | Usually weaker and variable over soil | Expect pattern and impedance to differ by site |
| Wave or roughness effect | Reduced coherent reflection plus diffuse scatter | Terrain and vegetation cause other irregularities | Do not assume a fixed gain advantage in all weather |
| Ground radials | Still useful; elevated radials give repeatability | Usually essential for high efficiency | Count and symmetry matter more than a single ground rod |
| Tuning | May shift with tide, shoreline, and moisture | May shift with soil moisture and nearby objects | Measure at the final installation site |
Recommended configurations
Portable beach station. Use a quarter-wave radiator with four evenly spaced elevated radials, a current choke at the feed point, and an analyzer measurement after placement. Keep the radial hub above splash range and allow for tide. If only surface radials are possible, use as many as practical and distribute them uniformly.
Permanent inland station. Use a ground-mounted vertical with at least 16 to 32 uniformly distributed radials when space permits. Increase radial count and coverage toward 60 to 120 when extracting maximum efficiency is the goal. On-ground radial length is not required to be exactly resonant; total coverage and count are generally more important.
Direct seawater installation. Treat corrosion, electrical safety, isolation, and local regulations as first-order constraints. An immersed ground conductor can help, but retain a controlled return system and confirm feedline common-mode current is suppressed.
Measurement checklist
- Measure resonance and feed-point impedance at the deployed site, not only at home.
- Use a common-mode choke at the feed point when the feedline should not radiate.
- Change one variable at a time: radial count, radial elevation, distance to water, or radial connection method.
- Compare received or transmitted signal levels over repeated intervals. A single contact is not a reliable efficiency measurement.
- Document tide stage, sea state, soil moisture, frequency, and radial geometry with every comparison.
Evidence and limitations
The ideal quarter-wave-over-perfect-ground model predicts an approximately 36 to 37 ohm radiation resistance and about 5.15 dBi directivity in the upper hemisphere. Real gain is that directivity multiplied by radiation efficiency, so ground loss, conductor loss, and counterpoise loss matter. A numerical or measured result for one beach cannot be transferred unchanged to another beach because the shoreline, radial arrangement, water conductivity, and receiver geometry can differ.
Sea-surface roughness should be described in terms of frequency, polarization, grazing angle, wind speed, and wave statistics. A broad claim such as “waves kill the saltwater effect” is not correct. Roughness primarily reduces the coherent far-field reflection and increases diffuse scattering; the highly conductive seawater can still provide a favorable local RF environment.
References
- Brown, G. H., Lewis, J., and Epstein, J. Ground Systems as a Factor in Antenna Efficiency. Proceedings of the IRE, 25(6), 753–787, 1937.
- Hill, D. A., and Wait, J. R. Calculated Pattern of a Vertical Antenna with a Finite Radial Wire Ground System. Radio Science, 8(1), 81–89, 1973.
- Weiner, M. M. Radiation Efficiency and Directivity of Monopole Elements with Disc Ground Planes on Flat Earth. Electronics Letters, 28(25), 2282–2283, 1992.
- Weiner, M. M., Zamoscianyk, S., and Burke, G. J. Radiation Efficiency and Input Impedance of Monopole Elements with Radial Wire Ground Planes in Proximity to Earth. Electronics Letters, 28(16), 1550–1551, 1992.
- Severns, R., N6LF. Some Thoughts on Vertical Ground Systems Over Saltwater. ARRL Antenna Book supplemental paper.
- Severns, R., N6LF. Elevated Versus Ground Radials. QEX, November/December 2009.
- International Telecommunication Union. ITU-R Recommendation P.527-6: Electrical Characteristics of the Surface of the Earth, 2021.
- International Telecommunication Union. ITU-R Recommendation P.2146-0: Sea Surface Bistatic Scattering, 2022.
- International Telecommunication Union. ITU-R Recommendation P.368-10: Ground Wave Propagation Prediction Method for Frequencies Between 10 kHz and 30 MHz, 2022.
- Yang, Y., et al. Parabolic Equation Modeling of Electromagnetic Wave Propagation over Rough Sea Surfaces. Sensors, 19(5), 1252, 2019.
- Liu, Y., et al. Research on the Additional Secondary Phase Factor for Automatic Identification System Signals Transmitted over a Rough Sea Surface. Sensors, 18(3), 697, 2018.
- American Radio Relay League. The ARRL Antenna Book and the Antenna Ground technical collection.