Established less than 1 year ago, AMSAT’s all-volunteer Phase 4 Ground Terminal team has made significant strides in developing an ensemble of solutions to support the so-called “Five and Dime” (5 GHz and 10 GHz) strategy AMSAT has embraced for microwave satellite projects. Prompting the effort is the planned launch of a geosynchronous military satellite in the 2018 timeframe, which could play host to an Amateur Radio payload operating on the two microwave band. The overarching project, which also includes a complementary Phase 4 Space team, is exploring new territory and innovative solutions, and it’s seeking volunteers from among the technically savvy within the Amateur Radio community.
“We’re going to make it as awesome as possible,” Ground Station team lead Michelle Thompson, W5NYV, told ARRL. The project not only would support the Phase 4B geosynchronous launch but provide solutions for the Phase 3E high-Earth orbit satellite, and receiver support for AMSAT’s entry into the NASA Cube Quest Challenge, which would go to the moon.
Thompson said the compelling technical reason for using 5 GHz and 10 GHz is the ability to use high-bandwidth modes on those bands. In addition, “the 5 and 10 GHz bands are popular elsewhere, and other projects are embracing this band complement,” she noted. Another advantage would be to raise Amateur Radio’s profile on the two bands and perhaps “shake things up” there for terrestrial use. “The 5 and 10 GHz bands are a compromise that’s working really, really well,” Thompson said.
The US Air Force will control the geosynchronous satellite. Virginia Tech, Millennium Space Systems (MSS), FEMA, various clubs as well as AMSAT and ARRL are partners in or are supporting the project. A formal memorandum of understanding is pending.
“We’re currently exploring the Amateur Radio implementation of a very advanced and exciting open standard called DVB-S2X for the downlink,” Thompson explained, noting it offers a variety of modulation and coding. Earth stations will use their individual radios, transmitting a digital signal — probably something called Offset QPSK (O-PSK) — directly to the satellite, with each getting its own channel in a frequency division, multiple access (FDMA) scheme. “This is an elegant way to design an efficient and advanced communication system and allows technical volunteers to experiment with the basics of cognitive radio — radio that can sense the environment and adapt to take full advantage of the capabilities the hardware offers,” she said.
Groundsats and a “Big Honking SDR”
Phase 4 radios will be designed to work not just with the impending geosynchronous satellite but through terrestrial microwave “Groundsats,” which, Thompson said, “are essentially satellite simulators that let you test and use the radio terrestrially.” Phase 4 radio designs also could be configured to use modulation schemes that are better able to deal with terrestrial multipath.
Amateur Radio Access Points (ARAPs) — essentially signal aggregators — would allow legacy radios, FM hand-held transceivers, or emergency traffic providers to use the satellite from any point where an ARAP can be deployed, packaging the input for uplink to the satellite. Hams within ARAP range would be able to use the Five and Dime terrestrial network just as if they were operating through a satellite.
“The Groundsat, which is doing the same job as the satellite payload, has a big honking SDR on it,” Thompson said. Groundsat equipment has arrived and is in use in San Diego, North Texas, and at Virginia Tech, and Groundsat development is under way at those sites. A fourth site would be at Morgan State University in Maryland.
Doing It on the Cheap
“Five and Dime” also reflects the project’s economics. AMSAT Board Member and Virginia Tech Research Professor Bob McGwier, N4HY, recently explained on the AMSAT-BB that the Ground Team’s work is “an effort to design an inexpensive ground terminal for amateurs that would cost tens of thousands of dollars commercially, for as much under $1000 as we can get it.” In contrast to the Space Team’s work, which, he said, is taking place “under the cloak of ITAR (International Traffic in Arms Regulations),” the Ground Team’s SDR is “completely open source, open specification” and “easily reprogrammed to do many different kinds of missions just by changing the software.”
“We welcome any interested technical volunteers to apply to the technical volunteer program at AMSAT and become part of the team,” Thompson said. To volunteer for the Phase 4 Ground Team, provide your contact information on AMSAT’s Engineering Team contact form. Thompson’s weekly “Phase4” engineering updates are available via YouTube. Additional development documentation is posted on GitHub.