Paulo Pinto / Amateur Radio Satellite Communications: A Comprehensive Guide

Created Wed, 28 May 2025 00:00:00 +0000 Modified Wed, 28 May 2025 11:25:40 +0100
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satellite hamradio cubesat AMSAT citizen science telemetry

Amateur Radio Satellite Communications: A Comprehensive Guide

Amateur radio satellite communications represent one of the most fascinating aspects of the hobby, combining radio technology, space science, and global connectivity. Since the launch of OSCAR 1 (Orbiting Satellite Carrying Amateur Radio) in 1961, radio amateurs worldwide have been communicating through an ever-evolving fleet of satellites, pushing the boundaries of what’s possible with relatively modest equipment.

How Amateur Radio Satellite Communications Work

At its core, satellite communication involves transmitting radio signals to a satellite in orbit, which then retransmits these signals back to Earth. However, the technical details make this seemingly simple concept both challenging and rewarding.

Basic Principles

Amateur radio satellites function as repeaters or transponders in space. When you transmit a signal (uplink) to the satellite, it receives this signal, processes it, and then retransmits it (downlink) back to Earth. This allows radio amateurs to communicate over much greater distances than would be possible with direct terrestrial communication.

The key components of satellite communication include:

  1. Uplink: The frequency on which you transmit to the satellite
  2. Downlink: The frequency on which you receive from the satellite
  3. Transponder: The equipment onboard the satellite that receives, processes, and retransmits signals
  4. Footprint: The area on Earth where the satellite’s signals can be received

Orbital Mechanics

Satellites used by radio amateurs typically operate in one of several orbit types:

  1. Low Earth Orbit (LEO): Most amateur satellites orbit between 200-2,000 km above Earth. These satellites move quickly across the sky, providing brief windows of communication (typically 5-15 minutes per pass).

  2. Medium Earth Orbit (MEO): These satellites orbit at higher altitudes (2,000-35,786 km), providing longer access times but requiring more powerful equipment.

  3. Geostationary Orbit (GEO): Satellites at approximately 35,786 km above the equator appear stationary from Earth. QO-100 (Es’hail-2) is currently the only amateur radio satellite in geostationary orbit, providing continuous coverage to about one-third of the Earth’s surface.

  4. Highly Elliptical Orbit (HEO): These satellites follow an elongated path, coming close to Earth at one point and reaching far into space at another. This provides extended coverage over specific regions.

The Doppler Effect

One of the most significant challenges in satellite communication is the Doppler effect. As a satellite moves toward or away from you, the apparent frequency of its signals changes. For LEO satellites, this shift can be substantial—up to several kilohertz—requiring operators to continuously adjust their frequencies during a pass.

The “One True Rule” of Doppler tuning, as explained by Paul Williamson (KB5MU), states that you should tune to compensate for Doppler on the highest frequency in use, whether that’s the uplink or downlink.

Equipment Needs

The equipment required for satellite communication varies depending on the satellite type, but typically includes:

  1. Radio(s): Either a dual-band radio capable of full-duplex operation or two separate radios
  2. Antennas: Directional antennas (Yagis, helicals, or log periodics) provide better performance, though omnidirectional antennas can work for strong satellites
  3. Rotators: Optional but helpful for tracking satellites across the sky
  4. Tracking Software: Programs like SatPC32, Gpredict, or mobile apps that predict satellite passes and help with Doppler correction

Types of Amateur Radio Satellites

Amateur radio satellites come in several varieties, each with distinct characteristics and operating modes:

FM Voice Satellites

FM (Frequency Modulation) satellites are the easiest entry point for beginners. They function as cross-band repeaters, typically receiving on one band and transmitting on another (e.g., 2 meters/70 cm).

Key characteristics:

  • Simple to operate with basic equipment (even handheld radios)
  • Use FM modulation, similar to terrestrial repeaters
  • Support voice communications
  • Usually operate in half-duplex mode
  • Popular examples include SO-50, PO-101, and the ISS repeater

Linear Transponder Satellites

Linear transponders are more sophisticated, supporting multiple simultaneous users across a range of frequencies.

Key characteristics:

  • Support SSB, CW, and other modes
  • Can accommodate multiple QSOs simultaneously within the transponder bandwidth
  • Require more precise frequency control and Doppler correction
  • Typically use less power than FM satellites
  • Popular examples include AO-7, FO-29, QO-100, and RS-44

Digital Satellites

Digital satellites employ various digital protocols for data transmission, telemetry, and sometimes voice.

Key characteristics:

  • Support packet radio, APRS, digital voice, and other digital modes
  • Often used for store-and-forward messaging
  • May require specialized software or hardware
  • Examples include the ISS APRS digipeater, NO-44, and various CubeSats

Telemetry Beacons

Many satellites transmit telemetry data that can be received and decoded by radio amateurs, providing valuable information about the satellite’s health and operations.

Key characteristics:

  • Transmit data about satellite systems (temperature, voltage, etc.)
  • Often use CW, RTTY, or specialized digital modes
  • Provide educational opportunities and contribute to satellite operations
  • Present on most amateur satellites as secondary functions

Active Amateur Radio Satellites

The following satellites are currently active and available for amateur radio operators to use. This list is current as of May 2025, but satellite status can change rapidly.

FM Voice Satellites

  • SO-50 (SaudiSat-1C): 2m uplink/70cm downlink, requires 67.0 Hz CTCSS tone
  • PO-101 (Diwata-2): Active by schedule, 70cm uplink/2m downlink
  • ISS Crossband Repeater: Activated periodically, check schedule for operations
  • SO-124 (HADES-R): Recently launched FM repeater
  • IO-86 (LAPAN-A2): Equatorial orbit, activated by schedule

Linear Transponder Satellites

  • AO-7: One of the oldest active satellites, operates when in sunlight
  • FO-29 (JAS-2): Activated by schedule due to low battery
  • AO-73 (FUNcube-1): Transponder activated by schedule
  • JO-97 (JY1Sat): V/U (Mode B) linear transponder
  • RS-44: Reliable linear transponder
  • QO-100 (Es’hail-2): Geostationary satellite with microwave transponder (2.4 GHz up/10 GHz down)
  • MO-122 (MESAT1): Linear transponder satellite

Digital Satellites

  • ISS APRS: 145.825 MHz packet digipeater
  • AO-123 (ASRTU-1): Digital modes satellite
  • SONATE-2: Experimental digital communications
  • GRBAlpha: Telemetry beacon and experimental communications
  • LASARsat: Digital communications platform

Upcoming Satellites

  • HADES-ICM: In commissioning stage, available soon
  • TEVEL2 Constellation: In commissioning stage, available soon
  • GRBBeta: Currently VHF only, full capabilities coming online soon

Inactive Amateur Radio Satellites

Many satellites have completed their missions but remain important in the history of amateur radio space communications:

  • AO-91 (RadFxSat / Fox-1B): End of mission
  • AO-85 (Fox-1A): First AMSAT Fox satellite, no longer operational
  • AO-92 (Fox-1D): Ceased operations in 2020
  • AO-95 (Fox-1E): Failed to reach orbit
  • LilacSat-1 (LO-90): Re-entered atmosphere in March 2019
  • FO-99 (NEXUS): No longer operational
  • OSCAR 1: The first amateur radio satellite, launched December 12, 1961, operated for 22 days
  • OSCAR 6: Pioneering satellite that operated from 1972-1977
  • OSCAR 8: Popular satellite from 1978-1983
  • OSCAR 10: First amateur satellite in highly elliptical orbit
  • OSCAR 13: Provided excellent DX capabilities from 1988-1996
  • AO-40: Advanced satellite with microwave capabilities, operated 2000-2004
  • AO-51: Popular FM satellite, operated 2004-2011

CubeSats and Citizen Science Projects

The CubeSat revolution has democratized access to space, allowing universities, small organizations, and even high schools to build and launch satellites. Many of these carry amateur radio payloads and offer opportunities for citizen science participation.

What are CubeSats?

CubeSats are small, standardized satellites built in units of 10×10×10 cm cubes (1U). They can be combined into larger configurations (2U, 3U, 6U, etc.). Their standardized form factor and relatively low cost have made space more accessible than ever before.

For amateur radio, CubeSats represent an exciting frontier where operators can:

  • Receive telemetry and science data
  • Participate in educational experiments
  • Help track and monitor satellite health
  • In some cases, use communication transponders

Notable CubeSat Projects with Amateur Radio Involvement

  1. Fox Project (AMSAT-NA): A series of 1U CubeSats carrying FM transponders and scientific experiments. The Fox satellites (AO-85, AO-91, AO-92) have provided valuable data on radiation effects in space.

  2. FUNcube (AMSAT-UK): Educational CubeSats with a focus on engaging students. AO-73 (FUNcube-1) continues to operate, transmitting telemetry that can be received and decoded by schools worldwide.

  3. BIRDS Project: An international CubeSat program coordinated by the Kyushu Institute of Technology in Japan, involving multiple countries. These satellites typically carry amateur radio digipeaters and voice message boards.

  4. QB50 Project: An international network of CubeSats for multi-point, in-situ measurements in the lower thermosphere and technology demonstration.

  5. PocketQubes: Even smaller than CubeSats (typically 5×5×5 cm), these satellites often carry amateur radio beacons that can be received with modest equipment.

How to Participate in Citizen Science

Amateur radio operators can contribute to satellite science in several ways:

  1. Telemetry Collection: Many CubeSats transmit telemetry that project teams need to collect. By receiving and submitting this data, you help monitor satellite health and contribute to mission success.

  2. SatNOGS Network: The Satellite Networked Open Ground Station network (https://satnogs.org/) allows anyone to build or use networked ground stations to track and receive data from satellites, contributing to a global database.

  3. FUNcube Data Warehouse: Specifically for FUNcube satellites, this platform collects telemetry from radio amateurs worldwide.

  4. University Partnerships: Many university CubeSat teams welcome assistance from the amateur radio community in tracking their satellites and receiving data.

  5. Building Ground Stations: Creating your own satellite ground station can range from simple (handheld radio and portable antenna) to sophisticated (automated tracking systems with SDR receivers).

Recordings of Amateur Satellite Communications

Hearing actual satellite communications can be invaluable for understanding what to expect. Here are some recordings of various satellite contacts and signals:

  1. FM Satellite QSO via SO-50: Listen to a typical FM voice contact through SO-50

  2. Linear Transponder Operation on AO-7: Example of SSB operation through a linear transponder

  3. ISS SSTV Transmission: Slow Scan TV images from the International Space Station

  4. CubeSat Telemetry Reception: Decoding telemetry from a university CubeSat

  5. QO-100 Geostationary Satellite: SSB contact via the Qatar-OSCAR 100 satellite

  6. APRS via ISS Digipeater: Packet radio through the International Space Station

Getting Started

If you’re interested in exploring amateur radio satellite communications:

  1. Start by listening: Use existing equipment to receive satellite signals before attempting to transmit.

  2. Begin with FM satellites: They’re the most accessible for beginners.

  3. Use satellite prediction software: Apps like Heavens Above, ISS Detector, or SatPC32 will help you know when satellites are passing overhead.

  4. Join the community: Organizations like AMSAT provide resources, newsletters, and forums to help you learn and connect with other satellite operators.

  5. Attend satellite demonstrations: Many hamfests and radio clubs offer live demonstrations of satellite operations.

Conclusion

Amateur radio satellite communications offer a unique blend of radio technology, space science, and global connectivity. Whether you’re interested in making voice contacts, experimenting with digital modes, or contributing to citizen science, there’s a satellite project that matches your interests.

As technology advances and more CubeSats reach orbit, the opportunities for amateur radio operators to engage with space continue to expand. The skills developed in tracking and communicating via satellites also transfer to other aspects of the hobby, from antenna design to digital signal processing.

The next time you look up at the night sky, remember that dozens of amateur radio satellites are orbiting overhead, ready to connect you with fellow operators around the world.

References

  1. AMSAT. (2025). Communications Satellites. Retrieved from https://www.amsat.org/two-way-satellites/

  2. AMSAT. (2025). For Beginners – An Amateur Radio Satellite Primer. Retrieved from https://www.amsat.org/introduction-to-working-amateur-satellites/

  3. AMSAT. (2018). FCC Part 97 Amateur Radio Licensing for CubeSats. Retrieved from https://www.amsat.org/wordpress/wp-content/uploads/2018/04/AMSAST_CubeSat_Licensing.pdf

  4. Baker, K. (2021). For Beginners – An Amateur Radio Satellite Primer. AMSAT Journal Compilation.

  5. Williamson, P. (n.d.). The One True Rule for Doppler Tuning. Retrieved from AMSAT resources.

  6. AMSAT-UK. (2025). Active Satellite Frequencies. Retrieved from https://amsat-uk.org/satellites/frequencies-of-active-satellites/

  7. SatNOGS. (2025). Amateur satellite database. Retrieved from https://db.satnogs.org/

  8. N2YO. (2025). Amateur radio satellites. Retrieved from https://www.n2yo.com/satellites/?c=18