Nonhams usually are pretty surprised to find out about ham radio satellites. Imagine — do-it-yourself satellites! The first amateur satellite, OSCAR-1 (Orbiting Satellite Carrying Amateur Radio), was built by American hams and went into orbit in 1961, just a couple of years after the Soviet Union launched Sputnik and ignited the space race.
As of early 2013, 25 active satellites were providing ham-to-ham communications or supporting the scientific experiments of student teams by sending telemetry back to Earth.
The main organization for amateur satellite activities is AMSAT. AMSAT coordinates the activities of satellite-building teams around the world and publishes the AMSAT Journal, which contains some interesting high-tech articles.
Ham radio satellite basics
Most amateur satellites are located in near-circular low Earth orbit, circling the planet several a times each day. A few have noncircular Molniya orbits that take them high above the Earth, where they’re visible for hours at a time.
Molniya is lightning in Russian and is the name given to a Russian fleet of communications satellites that travel in elliptical orbits.
For practical and regulatory reasons, satellite transmissions are restricted to the bands on 15 and 10 meters and to the 2 meter, 70 cm, and microwave bands at 1296 MHz and higher. The ionosphere doesn’t pass signals reliably at lower frequencies, and satellite antennas need to be small, requiring shorter wavelengths.
The satellite’s input frequencies are called the uplink, and the output frequencies are called the downlink. The pieces of information that describe a satellite’s orbit (and allow software to determine where it is) are called the orbital or Keplerian elements. Knowing where a particular satellite is in space allows you to operate through it.
There are four common types of satellites:
Transponder: A transponder listens on a range of frequencies on one band, translates those signals to a different band, and retransmits them in real time.
Repeater: Just like terrestrial repeaters, repeater satellites listen and receive on a specific pair of channels. Satellite repeaters are crossband, meaning that their input and output frequencies are on different bands.
Digital: Digital satellites can act as bulletin boards or as store-and-forward systems. You can access both types of digital satellites by using regular packet radio protocols and equipment. The International Space Station (ISS) has a digital bulletin board that’s available to hams on the ground, as well as an onboard APRS digipeater.
Store-and-forward satellites act as message gateways, accepting messages and downloading them to a few control stations around the world. The control stations also pass messages back up to the satellites that are downloaded by ground-based users. Digital satellites are very useful to hams at sea or in remote locations.
Telemetry: Many student teams and other noncommercial groups (whose members have licenses, like all other hams) use amateur radio frequencies to build small satellites called CubeSats, which are launched into low Earth orbit as a group when a commercial satellite launch has spare payload capacity.
Each CubeSat measures something or performs some interesting function and then sends a stream of digital data (telemetry) back to Earth. A CubeSat may or may not be controllable by telecommand from a ham station on Earth. CubeSats typically operate for less than a month; then they gradually reenter the atmosphere and burn up.
If you’re interested in supporting or working with a CubeSat team, check out the NASA CubeSat initiative.
How to access ham radio satellites
The best place to find out which satellites are active and in what mode is the AMSAT home page. Click the Sat Status link to get complete information about what each satellite does and its current operational status.
To access satellites, you also need a satellite tracking program. Several of these programs, including free and shareware trackers, are listed at The DXZone. AMSAT also provides several professional-quality tracking and satellite operation programs.
When you have the tracking software, obtain the Keplerian elements for the satellite you’re seeking from the AMSAT home page (click the Keplerian Elements link). Enter this information into your software program, and make sure that your computer’s time and date settings are correct.