Amateur satellites
| Amateur satellites | |
|---|---|
| Also called | OSCARs (Orbiting Satellite Carrying Amateur Radio) |
| First launched | OSCAR 1, December 1961 |
| Main organization (US) | AMSAT, the Radio Amateur Satellite Corporation, founded 1969 |
| Usual bands | 2 m and 70 cm; some also use 10 m, 23 cm and microwave bands |
| Operating | |
| Types | FM repeaters, linear transponders, digital and APRS |
| Typical pass | Up to about 10–15 minutes in low earth orbit |
| Simplest station | Dual-band FM radio and a handheld Yagi |
| US license | Technician and above |
| International Space Station | |
| Voice downlink | 145.800 MHz FM |
| Crossband repeater | Uplink 145.990 MHz (67.0 Hz tone), downlink 437.800 MHz |
Amateur satellites are spacecraft that carry radio equipment for licensed hams, usually a repeater or transponder that relays signals from one ground station to another. Because a satellite a few hundred miles up can see a patch of the earth thousands of miles across, a station with a handheld radio and a small antenna can talk across a continent during a pass lasting a few minutes. Hams have built and flown their own satellites since 1961, and most can be worked by any Technician with equipment for the 2-meter and 70-centimeter bands.
AMSAT and OSCAR numbers
The first amateur satellite, OSCAR 1, rode into orbit as a secondary payload in December 1961 and sent the letters "HI" in Morse code for about three weeks. OSCAR stands for Orbiting Satellite Carrying Amateur Radio. In 1969 US hams founded AMSAT, the Radio Amateur Satellite Corporation, which builds satellites, tracks those in orbit and publishes operating guides; sister AMSAT groups exist in many countries.
Once a new satellite is in orbit and working on amateur frequencies, its builders can ask AMSAT for an OSCAR number, with a prefix for the builder or country: AO-7 is AMSAT-OSCAR 7, FO-29 is Fuji-OSCAR 29 from Japan, and SO-50 is Saudi-OSCAR 50.
Kinds of satellite
- FM satellites, the "easy sats", are single-channel repeaters in orbit, usable with any dual-band FM radio and, usually, a CTCSS tone on the uplink. SO-50, launched in 2002, has been among the most worked.
- Linear transponders receive a slice of spectrum, typically tens of kilohertz wide, and retransmit the whole slice on another band, so many SSB and CW (Morse) contacts can share the satellite at once. Most are inverting: a signal at the bottom of the uplink comes out at the top of the downlink, so operators transmit lower sideband to be heard on upper sideband. AO-7, launched in 1974, fell silent in 1981 and came back to life in 2002, and it still works when in sunlight.
- Digital satellites carry packet and APRS digipeaters, store-and-forward systems and telemetry beacons.
- QO-100, launched in 2018, carries the first geostationary amateur transponders, covering Europe, Africa, the Middle East, much of Asia and the eastern edge of South America but not North America.
Satellites fail and new ones are launched every year, so the list of working satellites changes constantly; AMSAT keeps a current status page.
The International Space Station
Amateur radio from space began on the Space Shuttle Columbia mission STS-9, launched on November 28, 1983, and landed on December 8. Astronaut Owen Garriott, W5LFL, made contacts in his free time with a 5-watt Motorola handheld and an antenna mounted in a shuttle window; the first station he worked was Lance Collister, WA1JXN. The Goddard Amateur Radio Club station, WA3NAN, retransmitted shuttle audio around the clock so hams everywhere could follow along. Garriott's success led to SAREX, the Shuttle Amateur Radio Experiment, on later shuttle flights, and crews of the Russian space station Mir also used ham radio. ARISS is the successor to SAREX. In 2008 Owen Garriott's son Richard Garriott, W5KWQ, operated from the International Space Station, making the two the first American father and son to make ham radio contacts from space.
The ISS carries amateur stations operated under ARISS (Amateur Radio on the International Space Station), a partnership of space agencies and amateur organizations including AMSAT and the ARRL. Its best-known work is the school contact: ARISS schedules a pass during which students take turns asking an astronaut questions by radio, through a ground station at the school or one elsewhere linked by telephone. A good pass gives about ten minutes.
When the crew isn't using the radio, it often runs as an FM crossband repeater, with its uplink on 145.990 MHz (67.0 Hz tone) and its downlink on 437.800 MHz. Voice contacts come down on 145.800 MHz. Slow-scan television events in 2026 used 437.550 MHz. The packet and APRS digipeater frequencies are 145.825 MHz and 437.825 MHz; as of October 2026, APRS was running on 437.825 MHz from a radio still being tested. What is switched on varies, so check the ARISS status page and announcements before a pass.
Ham radio has flown on other crewed spacecraft too. On the Fram2 mission, the first crewed flight in a polar orbit, launched on 31 March 2025, pilot Rabea Rogge, LB9NJ and KD3AID, used a battery-powered Icom IC-705 to make the first amateur radio contact from a SpaceX Crew Dragon: on 1 April she answered questions from students at the Technical University of Berlin on 437.550 MHz. She also sent slow-scan television pictures of the polar regions for Fram2Ham, a competition for student teams, and amateurs around the world decoded them. In 2026, when NASA sent the Artemis II crew around the Moon, it invited outside volunteers to track the Orion spacecraft's radio signals passively with their own equipment; the 34 chosen included amateur groups such as AMSAT Deutschland, AMSAT Argentina and CAMRAS, and university teams such as one from the University of Pittsburgh, whose Panther Amateur Radio Club picked up Orion's carrier on the mission's second and fourth days with a 1.2-meter dish and a software-defined radio. NASA's own networks remained the mission's main tracking and communications links.
Working a satellite
Low-orbit satellites circle the earth roughly every 90 to 120 minutes and come within range of any one station a few times a day. Pass prediction tools, such as AMSAT's online predictor, Heavens-Above, the free Gpredict program and phone apps, show when each satellite will rise and where to point. Many give times in UTC.
The classic beginner's station is a dual-band HT and a handheld dual-band Yagi such as the Arrow, with a few elements for each band on one boom. The operator aims it by hand, following the satellite across the sky and twisting it to follow the changing polarization. Satellite work is full duplex: you listen to the downlink while transmitting on the uplink, which is how you know you are getting through. Most HTs cannot receive while transmitting, so many operators transmit with one radio and listen with a second radio or a software-defined receiver, using an earphone to avoid feedback.
Doppler shift raises the frequency as the satellite approaches and lowers it as it recedes, by up to about 3 kHz on 2 meters and 10 kHz on 70 centimeters. The convention is to correct on the higher-frequency side, usually 70 centimeters, and leave the 2-meter side fixed; on an FM satellite that means a few memory channels 5 kHz apart, stepped through during the pass. Linear transponders need continuous tuning, which programs such as SatPC32 can do automatically by controlling the radio.
An FM satellite is one channel shared by everyone under its footprint, so contacts are brief: call signs, grid squares, perhaps a name. Wait for a gap, keep transmissions short and use no more power than it takes to hear yourself.