High School Marine Buoy Transmitter Now Active on 20-Meter WSPR

Phil Karn, KA9Q; Randy Standke, KQ6RS, and members of the Mount Carmel High School Amateur Radio Club (MCHSARC) in San Diego have constructed and deployed an amateur radio marine buoy in the Pacific. The buoy, which transmits WSPR on 14.0956 MHz USB, has already been heard around the continental US, Brazil, Hawaii, Japan, Costa Rica, Australia, and South Africa.

“Over the past year, Randy and I have mentored the MCHSARC in designing and constructing a simple marine buoy that was deployed from the RV Sally Ride [on July 16], about 700 kilometers off the coast of southern California,” Karn said in a post on the AMSAT Bulletin Board. “It is up and transmitting WSPR on 20 meters using the call sign KQ6RS, and is being received all over the US and into Canada and Brazil.” Karn is blogging about the project with updates.

The electronics are the 20-meter WSPR version of the WB8ELK “pico tracker” that has been flown on long-duration balloons. “We removed the solar panels and substituted 21 ordinary alkaline D cells, wired to supply 4.5 V,” Karn explained. “We estimate the battery lifetime will be 6 months.”

Karn said that the project made use of everyday hardware. The buoy — essentially a spar buoy — was constructed using a 5-foot section of 4-inch PVC pipe, with sufficient ballast in one end of the pipe to permit it to float vertically in the water. The top is closed using a sewer pressure test plug, which has a bolt in the center that acts as a convenient feed-through and antenna mounting point. The antenna is a stainless-steel CB whip with a matching network.

“We use the sea as a counterpoise, but to avoid direct metal/seawater contact, we lined the inside of the pipe with copper tape to form a capacitive connection,” Karn said.

During initial flotation testing, the project team found that the ballasted pipe alone was remarkably stable in pitch, roll, sway, and surge, but oscillated a lot in heave — i.e., up and down movement. Cross arms were at the water line to add drag in the vertical direction, to counter the issue.

“It wasn’t our intent to mimic a religious icon, but that’s where the physics went,” Karn said. Because seawater was required to tune the antenna, Standke floated the buoy off a dock in Mission Bay.

“We tried to make this thing as rugged as we could,” Karn recounted, offering his favorite saying to the students: “The sea always wins in the end, but we can delay that long enough to be useful.”

Deployment was to be from an NOAA vessel in April, but the trip was canceled due to the COVID-19 pandemic. Standke secured a trip on the RV Sally Ride, a research vessel operated by the Scripps Institute of Oceanography.

The first reception report was on July 16 at 12:52:30 UTC from grid square CL89eu, although the current carried the buoy east into CL89fu at 20:32:30 UTC. The buoy (KQ6RS-1) can be tracked on the APRS and WSPRnet sites.

Karn said the project team is already planning its second buoy, which may include two-way links, satellite tracking, and sensors

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