Amateur Satellites
This section covers communication through satellites in low Earth orbit and the amateur radio payload on the International Space Station. Operators transmit uplink signals that are received, frequency-shifted, and retransmitted on the downlink. Linear transponders accept SSB or CW across a several-kilohertz passband while FM repeaters and packet digipeaters handle single-channel voice or APRS-style data. The ISS supports both FM voice and store-and-forward packet on the same VHF and UHF allocations used by dedicated satellites.
Orbital mechanics and pass geometry
Most active satellites occupy circular or near-circular orbits between 300 and 1200 km altitude. A single pass lasts from five to fifteen minutes depending on maximum elevation. Because the satellite moves at several kilometres per second relative to the ground station, the geometry changes continuously; the operator must adjust both azimuth and elevation to keep the antenna pointed at the moving target. Two-line element sets distributed by orbital tracking services supply the instantaneous position data that tracking programs convert into real-time pointing commands.
Equipment and signal path
A typical station uses a directional antenna such as a crossed Yagi or helical array on 144 MHz or 435 MHz. The receiver must resolve signals that are 20 to 30 dB weaker than terrestrial contacts because of free-space path loss and the small satellite antennas. Many operators employ full-duplex transceivers so they can hear their own downlink while transmitting. Computer-controlled rotators and Doppler-compensating software keep the received frequency within the narrow SSB filter as the satellite approaches and recedes. Circular polarisation at both ends reduces fading caused by Faraday rotation in the ionosphere.
Tracking in practice
Prediction begins with loading fresh orbital elements into software that calculates rise time, maximum elevation, and set time for the station latitude and longitude. During the pass the operator follows the changing azimuth and elevation while tuning to offset the Doppler shift, which can reach several kilohertz on 435 MHz. On linear satellites the operator also selects an uplink frequency that lands inside the downlink passband after the satellite’s translation offset is applied. Successful contacts require the satellite to be above both stations’ horizons simultaneously and for both antennas to maintain lock throughout the window.
Persistent difficulties
Operators disagree on whether FM-only satellites or linear transponders offer the better learning path; the former are simpler to operate yet support fewer simultaneous contacts, while the latter demand precise frequency coordination and better antennas. Accurate orbit prediction remains a recurring problem because atmospheric drag and infrequent element updates cause cumulative errors that shift a predicted pass by several minutes. Polarisation mismatch, spin modulation of the satellite antennas, and local obstructions that clip low-elevation passes further reduce the fraction of usable time. New operators frequently underestimate how quickly the geometry changes near overhead passes and lose lock before the satellite reaches maximum elevation.
From this page move to the equipment and antenna construction resources, then to the current orbital element sources and tracking software notes. Those sections supply the concrete details needed to assemble a working station and schedule the next pass.
ARRL bulletins
ARRL headquarters in Newington issued regular bulletins that summarised satellite launch schedules, orbital status and contact reports from amateurs. These bulletins reached members through packet networks and early web postings, giving operators the only central source of coordinated information before dedicated tracking sites existed. The arrangement ended when AMSAT took over most real-time status distribution and ARRL shifted its emphasis to regulatory and educational material.
AMSAT satellite programmes
AMSAT designed and coordinated a series of spacecraft that moved from low-Earth-orbit beacons to elliptical-orbit transponders. The Phase 3 series introduced higher orbits that extended pass duration and reduced the number of stations needed for intercontinental links, at the cost of more complex antenna pointing and greater launch energy requirements. Later projects encountered repeated delays when primary rocket opportunities were cancelled, forcing reliance on secondary payload slots.
Russian spacecraft and Mir operations
Russian Progress supply vehicles and the Mir station carried amateur payloads that operated alongside crew activities. Cosmonauts and visiting astronauts used the station’s VHF and UHF equipment for voice contacts and packet exchanges with ground stations. Amateur operation from Mir ran from the late 1980s until the station was deorbited in 2001, and the same frequencies and modes later transferred to the ISS amateur radio installation.
NASA missions and SAREX
Shuttle missions under the Space Amateur Radio Experiment carried portable transceivers that allowed astronauts who held licences to operate during orbital passes. The programme demonstrated that crew members could conduct scheduled school contacts and random QSOs without interfering with primary mission tasks. After the shuttle fleet retired, the same equipment concept moved to the permanent ISS amateur station.
Amateur payloads on launch vehicles
Early amateur satellites rode as secondary payloads on government and commercial rockets. Builders had to meet strict mass, vibration and frequency-coordination rules set by the primary mission; successful integration gave access to orbit at far lower cost than a dedicated launch, but also meant the amateur payload launched only when the main customer’s schedule permitted. Several Russian-built RS-series satellites followed this route before dedicated small-satellite deployers became common.
Where to go next
Further reading