Amateur Radio Buoys—Bringing HF Position Reporting to the Open Ocean
Amateur radio encompasses a wide variety of unique pursuits. While many operators focus on standard HF propagation, satellite communications, or moonbounce, Randy, KQ6RS, pursues a distinct niche: building amateur radio buoys.
These buoys transmit their grid squares and geographic coordinates using the Weak Signal Propagation Reporter (WSPR) digital mode on the HF bands. He constructed his early buoys using standard materials that one might find in the plumbing section of a hardware store, demonstrating how accessible engineering can produce surprisingly sophisticated results. One of his battery-powered designs used only 20 milliwatts of RF power—supplied by a custom pack of 21 D-cell batteries—to transmit signals across the ocean for months at a time.
The concept behind these buoys is relatively straightforward: create an inexpensive, self-contained radio transmitter that can float freely in the ocean while reporting its position. WSPR is particularly well suited to this application because it was designed to detect low power and weak signals buried deep below the noise floor (-34 dB SNR).
Each transmission allows receiving stations around the world to record the buoy’s callsign and location. A GPS module on the buoy records its position and subsequently transmits the eight-character grid square for WSPR stations to receive. Unlike a conventional beacon installed at a fixed location, a floating buoy can travel hundreds of miles with ocean currents while continuing to transmit. Its position reports consequently become a record of both radio propagation and ocean movement.
The first-generation buoy’s construction illustrates Randy’s resourcefulness. Its housing was assembled from PVC plumbing components, providing a lightweight, inexpensive enclosure for the electronics and batteries. The power system consisted of 21 alkaline D-cell batteries arranged as three series-connected groups of seven parallel batteries. This configuration supplied approximately 4.8 volts when new, gradually declining as the batteries discharged. With the electronics drawing approximately 28 milliamps, the battery pack was designed to provide roughly six months of operation—an impressive service life.
Building a functioning transmitter, however, was only part of the challenge. The antenna had to operate efficiently despite being only about seven feet above the ocean surface. Such a short antenna presents a difficult impedance-matching problem, particularly on the 20-meter band near 14.1 MHz. Randy addressed this using a custom network of inductors to transform the antenna’s electrical impedance into something closer to the 50-ohm impedance expected by the transmitter. The surrounding ocean also played an important role: Its high electrical conductivity provides an effective RF ground plane. These design details helped the buoy radiate its low-power signal while remaining compact enough to float on the water.
Mechanical reliability presented another challenge. In a subsequent design, Randy experimented with a six-foot fiberglass driveway-marker rod to support the antenna wire. Earlier PVC antenna supports could break if a buoy tipped over against a hard surface. The fiberglass rod offered greater flexibility, but attaching it securely required careful engineering. He tested different epoxies, discovered that some shrank significantly while curing, and developed a water-cooled curing process that produced a tighter fit. He also engineered waterproof connections and pressure-tested the enclosure to prevent water from entering.
Randy later took the concept further in the most recent version of the buoy by adapting a commercial NexSens CB-150 environmental monitoring buoy into a solar-powered amateur radio platform. Rather than relying exclusively on disposable batteries, this substantially larger buoy used three solar panels positioned around its upper structure, a charge controller, and two 12-volt, 8.5-amp-hour batteries. Together, the batteries stored approximately 200 watt-hours of energy. The solar panels replenished this reserve during daylight, allowing its location to be potentially relayed indefinitely via WSPR.
Both PVC and solar-powered buoys incorporated GPS positioning and additional telemetry, including battery voltage and water temperature. Their electronics were designed to encode this information into the WSPR transmissions that could subsequently be decoded and displayed through APRS-related tracking services. This allowed observers to monitor more than just the buoy’s location. They could also assess its power system and environmental conditions remotely.
Randy documented the buoy’s launch from the research vessel “Sally Ride” on November 7, 2023, at approximately 29.8 degrees north latitude and 123.6 degrees west longitude, roughly 680 kilometers offshore from California. Subsequent position reports seen on wsprnet.org and APRS.fi under the callsign KQ6RS-12 over the next two-and-a-half years documented its movement through the Pacific Ocean, where its last transmission was received on October 10, 2026, at 06:06 UTC before potentially running aground on the Japanese island of Yakushima, easily outlasting the previous PVC D-cell powered buoys.
Reflecting on the deployment data, Randy noted that future iterations could benefit from a few key design adjustments. For instance, while the BME 280 sensor used onboard was capable of measuring temperature, pressure, and humidity, only temperature was utilized. Reporting internal humidity would have provided immediate, vital telemetry to confirm whether a leak had occurred.
Furthermore, the telemetry payload required custom modifications to the standard WSPR encoding typically used by high-altitude balloons. Because a floating buoy remains at sea level, the encoding scheme was cleverly adapted by trading altitude reporting for a tenfold reduction in position step size and sacrificing GPS quality reporting to provide a dedicated channel for improved temperature telemetry.
Beyond firmware and telemetry adjustments, hardware performance also presented lessons for the future. While the low-power setup was a technical success, signal strength proved to be a frequent hurdle. The 10mW signal was marginal much of the time—occasionally resulting in radio silence for about a week—even though ample DC power was available to run an amplifier. Upgrading to a 100mW (+20 dBm) amplifier would have significantly improved reception reliability.
Together, these projects demonstrate the intersection of amateur radio, electronics, mechanical engineering, and oceanographic observation. From inexpensive PVC pipe and D-cell batteries to a solar-powered commercial marine buoy, Randy’s designs show how an amateur radio beacon can become a long-duration, mobile scientific instrument.
Operating at just tens of milliwatts, these buoys offer a practical way to investigate HF propagation while tracking the movement of objects across the ocean. Their greatest achievement may be their simplicity. Using readily available components and careful experimentation, a small radio transmitter can turn the vast Pacific Ocean into a platform for continuous radio experiments.
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