Students at the US Naval Academy in Annapolis, Maryland, are planning an Amateur Radio CubeSat — dubbed HFSAT — that would carry an HF transponder as a primary payload as well as 2-meter APRS as a secondary mission when power is available. The 1.5 U CubeSat will have a linear uplink at 21.4 MHz and a downlink at 29.42 MHz.
“HFSAT is a small 1.5U CubeSat that will demonstrate the viability of HF satellite communications as a back-up communication system using existing ubiquitous HF radios that are often a part of the every amateur station,” said USNA Instructor Bob Bruninga, WB4APR, who developed APRS. Bruninga said HFSAT would be similar to the 1990s-era RS-12/13 Russian Amateur Radio satellite.
“HFSAT will continue the long tradition of small amateur satellites designed by students and hams at the US Naval Academy,” Bruninga told ARRL. The uplink will be at 21.4 MHz and downlink at 29.42 MHz, similar to [earlier] Mode K HF satellites. No launch has yet been identified.” Bruninga said HFSAT would be gravity gradient-stabilized by its full-sized, 10-meter, thin-wire, half-wave HF dipole.
Other unique features of HFSAT include its APRS telemetry command-and-control capability. “For VHF the students have modified a popular Byonics.com MTT4B all-in-one APRS Tiny-Track4 module for telemetry, command, and control to fit on a single 3.4-inch square card inside the CubeSat, that they will use for this and for future CubeSats,” Bruninga said. The students are working with Bill Ress, N6GHZ, on the HF transponder card, which will provide a bandwidth of 30 kHz with an inverting transponder to minimize Doppler. Todd Bruner, WB1HAI, will be the HFSAT control operator.
Bruninga said the HF transponder is a follow-on from the USNA’s existing PSAT 10-meter PSK31 transponder, still operational. HFSAT’s telemetry downlink will be captured via stations in the worldwide ground-station network. The packet link is a secondary mission compared to the HF transponder on this spacecraft.
Once HFSAT is in space, Bruninga recommended using a vertical HF antenna, because it would match well with the antenna patterns and geometry of Low Earth Orbit (LEO) satellites. “When low on the horizon, both the satellite and the user antennas are in their main lobes, providing maximum gain at the distant horizons,” Bruninga said. “At the higher elevations, the satellite is 6 dB to 10 dB closer, significantly making up for the reduced antenna pattern geometry.”