Ham Radio Satellite Operating Guide — LEO Satellites & Beyond
Working a DX station through a satellite passing at 800 km altitude is one of amateur radio's most technically satisfying achievements — and it is more accessible than most operators realise. The FM satellites (SO-50, AO-91, AO-92) can be worked with a handheld radio and a simple dual-band Yagi for under £50. The linear transponder satellites (IO-117, AO-73) reward a proper dual-band station with directional antennas and open up genuinely worldwide contacts via a single repeater in the sky. This guide covers the complete satellite operating toolkit.
Amateur satellites in Low Earth Orbit (LEO) circle the Earth at altitudes of 400–1,500 km, completing an orbit in 90–120 minutes. From any ground station, a LEO satellite is above the horizon for 8–15 minutes per pass. The contact window opens when the satellite rises above your local horizon (typically defined as 5° elevation to account for obstructions), reaches maximum elevation (AOS to LOS), then sets below the horizon. During this window you can make contacts through the satellite — with stations anywhere in the satellite's footprint, which at 800 km altitude is approximately 5,000 km in diameter.
FM satellites (easiest)
Single-channel FM repeater in the sky. Uplink on 70 cm, downlink on 2 m (or vice versa). Work them with a dual-band handheld radio and crossed-Yagi or Arrow antenna. No SSB or frequency tuning needed. Access controlled by a PL tone (typically 67.0 Hz). Current active FM sats: SO-50, AO-91, AO-92, TEVEL series.
Linear transponder satellites
A passband transponder that inverts and retransmits a 30–100 kHz slice of spectrum. Multiple simultaneous SSB/CW QSOs pass through the same satellite simultaneously. Uplink on one band, downlink on another. Requires SSB radio capable of both 2m and 70cm, plus Doppler correction. Current: AO-7, AO-73, IO-117, CAS-4B.
High Earth Orbit (Phase 3)
Satellites in elliptical orbits reaching 35,000–60,000 km apogee provide passes lasting hours rather than minutes. AO-10 operated for years in this mode. Currently no active Phase 3 satellites but AMSAT plans future missions. Require high-gain directional antennas and substantial EME-class stations.
| Satellite | Uplink (MHz) | Downlink (MHz) | Mode | PL/Notes |
|---|---|---|---|---|
| SO-50 (SaudiSat-1C) | 145.850 | 436.795 | FM | PL 67.0 Hz — most reliable FM sat |
| AO-91 (RadFxSat) | 435.250 | 145.960 | FM | PL 67.0 Hz |
| AO-92 (Fox-1D) | 435.350 | 145.880 | FM | PL 67.0 Hz |
| AO-73 (FUNcube-1) | 435.130–435.160 | 145.950–145.970 | Linear/SSB | Inverting transponder |
| AO-7 | Mode B: 432.125–432.175 | 145.975–145.925 | Linear/SSB | Inverting — very old satellite, intermittent |
| IO-117 (TEVEL-7) | 435.600 | 436.400 | FM | Check AMSAT for current status |
| ISS (NA1SS) | 144.490 (APRS) | 145.800 (FM voice) | FM / APRS | Crew schedules change — check ARISS |
A satellite moving toward you at orbital velocity compresses the radio waves it transmits — you receive a higher frequency than the satellite transmits. As the satellite moves away the frequency is stretched and you receive lower. This Doppler shift is significant at VHF/UHF: on 145 MHz, the maximum Doppler shift for a typical LEO satellite is approximately ±3.4 kHz. On 435 MHz it is approximately ±10 kHz. For FM satellites the FM discriminator handles moderate Doppler — just keep the squelch open throughout the pass. For linear transponder satellites, Doppler must be continuously corrected by manually tuning your radio or using computer-controlled Doppler correction software.
where f0 = nominal frequency, v_radial = satellite radial velocity (m/s), c = 3e8 m/s
Max radial velocity for LEO at 800km: ~7,000 m/s
Max Delta_f at 145 MHz: 145e6 x 7000 / 3e8 = +/- 3,383 Hz
| Frequency | Max Doppler shift (LEO 800km) | Rate at horizon | Correction method |
|---|---|---|---|
| 145 MHz (2m uplink) | ±3.4 kHz | ~20 Hz/sec at horizon | FM: automatic / SSB: manual or software |
| 435 MHz (70cm uplink) | ±10.2 kHz | ~60 Hz/sec at horizon | SSB: requires software Doppler correction |
| 1296 MHz (23cm) | ±30.3 kHz | ~180 Hz/sec | Software control essential |
| 2.4 GHz (S-band) | ±56 kHz | ~330 Hz/sec | Software control essential |
Satellite Doppler Shift Calculator
You cannot work a satellite without knowing when it will be visible and in which direction to point your antenna. Pass prediction software uses Two-Line Element sets (TLEs) — precise orbital data published by NORAD — to calculate exactly when each satellite will rise, reach maximum elevation, and set at your location, along with the azimuth and elevation at each moment of the pass.
Gpredict — the standard free tool
Gpredict (gpredict.oz9aec.net) is the most widely used free satellite tracking program among amateur operators. It runs on Linux, Windows, and macOS, provides real-time satellite tracking on a world map with footprint circles, generates pass tables showing AOS/TCA/LOS times and elevations for any future period, interfaces with CAT-controlled radios for automatic Doppler correction, and interfaces with rotator controllers for automatic antenna pointing. The pass table exported to PDF or printed is the essential planning document for a satellite operating session.
Other tracking tools
- SatPC32 (DK1TB): Windows-only, extensive rotor and radio control integration, widely used for serious satellite stations with motor-driven antennas
- Orbitron: Windows shareware, excellent visual display, popular for beginners
- ISS Detector / Look4Sat (Android): Mobile apps for portable satellite operation — show pass times and compass bearing in real time, essential for handheld portable satellite operation
- heavens-above.com: Web-based pass predictions for any location — useful for quick checks without installing software
FM satellites — handheld operation
The FM satellites (SO-50, AO-91, AO-92) can be worked with surprisingly simple equipment. Many operators make their first satellite contact with a dual-band handheld radio and a handheld Arrow or Elk dual-band Yagi — a commercially available lightweight antenna with a 2 m element and a 70 cm element on a single boom, weighing under 500 g. The operator holds the antenna and manually tracks the satellite across the sky by feel and by tuning the received downlink signal for maximum strength. No rotator, no computer control, no Doppler correction software — just a radio and antenna and the satellite tracking app on a phone.
Linear transponder satellites — fixed station
For the linear transponder satellites (AO-73, AO-7), horizontal polarisation and proper Doppler correction are needed. A fixed station uses a 2 m SSB/CW Yagi for the downlink and a 70 cm SSB Yagi for the uplink, both mounted on an azimuth-elevation rotator that tracks the satellite through the pass. The radio must be SSB-capable on both 2 m and 70 cm simultaneously (or two separate radios). Gpredict or SatPC32 provides automatic Doppler correction via CAT control, continuously adjusting the operating frequencies so the apparent frequency remains constant as the satellite moves.
Crossed-Yagi for circular polarisation
Satellite signals undergo Faraday rotation in the ionosphere — the polarisation plane rotates as the signal travels through the ionosphere, making linear polarisation unpredictable. A crossed-Yagi (two identical Yagi antennas mounted at 90° to each other on the same boom) fed with a 90° hybrid coupler produces circular polarisation (RHCP or LHCP depending on which input is used and the phasing). Circular polarisation is immune to Faraday rotation — a signal arrives correctly polarised regardless of how the ionosphere has rotated it. For serious satellite work, RHCP crossed Yagis on both uplink and downlink significantly improve contact success rates compared to linear polarisation antennas.
Making Your First Satellite Contact — Step by StepVerify the target satellite (SO-50 is a good first choice) is operational at amsat.org/status. Open Gpredict or your satellite tracking app and find an upcoming pass with a maximum elevation above 20° — lower passes are often blocked by terrain and buildings. Note the AOS time (when it rises above 5°), TCA time and azimuth (highest point), and LOS time. A 30° maximum elevation pass gives you approximately 8–9 minutes of contact window.
Program your dual-band radio (or two separate radios) with the satellite's uplink and downlink frequencies. For SO-50: uplink 145.850 MHz FM, downlink 436.795 MHz FM, PL tone 67.0 Hz on uplink. For a handheld setup, extend the Arrow or Elk antenna and move to an open area with a clear sky view. If possible, position yourself so the pass is in the clearest part of the sky (check the azimuth at TCA from your tracking app).
Start listening on the downlink frequency 2 minutes before the predicted AOS time. The FM satellite's downlink carrier should become audible as the satellite rises above your horizon — you will hear other operators transmitting through it. Monitor the signal strength: it increases from AOS to TCA, then decreases toward LOS. If you hear no signal by 2 minutes after predicted AOS, either the satellite is not active, your TLE data is old, or the pass azimuth was blocked by a building or terrain feature.
Wait for a brief gap between operators, then transmit your callsign clearly: "CQ satellite, [your callsign], CQ." Listen for a response on the downlink. The FM satellite allows multiple QSOs in sequence. Keep transmissions brief — the contact window is only 8–15 minutes and is shared with all operators in the satellite's footprint (potentially thousands of square kilometres). A typical FM satellite QSO is callsign exchange, grid square, and signal report — under 60 seconds total.
For FM satellites, the FM discriminator handles Doppler — no manual correction is needed. You may notice the downlink audio sounds slightly different early in the pass vs. late in the pass due to Doppler, but FM demodulation handles this automatically. For linear transponder satellites, you must manually tune the downlink receiver to compensate: retune upward approximately 3 kHz at AOS, tune back to nominal at TCA, tune downward 3 kHz approaching LOS — or use Gpredict's CAT control to automate this.
Record the satellite name, date, UTC time, the other station's callsign, and their reported grid square (Maidenhead locator). From the grid square you can calculate the great-circle distance of the contact — satellite contacts of 3,000–5,000 km are routine on FM satellites. Submit the contact to AMSAT's satellite contact log database and, if applicable, to your national satellite award scheme. AMSAT offers the OSCAR award for contacts made via a specified number of different satellites.
The linear transponder satellites carry a passband repeater that accepts a range of uplink frequencies (typically 30–100 kHz wide) and simultaneously retransmits all signals it receives — inverted in frequency — on the downlink band. An inverting transponder means that an uplink at the low end of the passband appears at the high end of the downlink passband. Multiple operators can use the satellite simultaneously as long as their uplink signals are on different frequencies within the passband. The transmitted power of each operator's station appears at a corresponding frequency in the downlink passband — like a full-duplex linear translator that anyone can use.
To operate on a linear transponder, you must transmit on the uplink band and simultaneously listen on the downlink band. Tune your own downlink until you can hear your own transmitted signal coming back from the satellite — this confirms you are in the transponder passband and working correctly. Then tune for other operators on the downlink and respond to them, adjusting your uplink frequency until your downlink signal lands on their frequency. Doppler correction is essential — as the satellite moves, you continuously retune to keep your signal at the correct frequency in the passband.
Frequently Asked QuestionsWhat licence do I need to work amateur satellites?
In most countries, satellite operation requires at minimum a full (Intermediate or General equivalent) licence rather than a Foundation/Technician licence, because satellite operation often involves 70 cm uplinks which may require a higher licence class. In the UK, Foundation licensees can use 2 m but not 70 cm — so FM satellites with 70 cm uplinks (SO-50, AO-91) require at minimum an Intermediate licence. Check your national licence terms before transmitting through any satellite.
Can I work satellites with a handheld radio?
Yes — the FM satellites (SO-50, AO-91, AO-92) are routinely worked with 5 W handheld transceivers and a handheld dual-band Yagi. The Arrow 146/437-10BP is the most popular choice. Some operators even work the FM satellites with an HT and its rubber duck antenna during high-elevation passes, though results are inconsistent. A proper dual-band Yagi dramatically improves reliability.
What is the grid square and why is it important for satellite contacts?
The Maidenhead grid square (e.g. IO91) is a 6-character location code used universally in VHF and satellite amateur radio contacts. It encodes your location to within approximately 5 km. Exchanging grid squares is the standard satellite contact format — from the grid you can calculate distance, and collecting contacts from many different grid squares is the basis of VHF and satellite award programs. Your grid can be found from your postcode at levinecentral.com/ham/grid_square.php or from GPS coordinates.
How do I avoid interfering with other satellite operators?
On FM satellites, wait for a pause between transmissions before calling CQ. Never transmit over another QSO in progress. Keep exchanges brief and efficient. On linear transponder satellites, listen first to understand how busy the transponder is before transmitting. Do not park your signal on a single frequency in the passband for extended periods — move frequency if someone is trying to call through the same frequency. The satellite passband is a shared resource.
What is the ISS packet radio system?
The International Space Station carries an amateur APRS digipeater on 144.825 MHz (US) or 145.825 MHz (international) — it retransmits APRS position packets from the ground. You can see your APRS packet appearing via the ISS using any APRS-capable radio and a simple 2 m vertical antenna. The ISS also periodically activates a voice repeater and SSTV transmitter — check ariss.net for scheduled activations, which are widely publicised in advance.
What is the OSCAR numbering system?
OSCAR (Orbiting Satellite Carrying Amateur Radio) is the naming system for amateur satellites. Each satellite receives an OSCAR number upon successful orbit — the first was OSCAR 1 in 1961. The prefix indicates the sponsoring organisation: AO (AMSAT-OSCAR), SO (Saudi-OSCAR), FO (Fuji-OSCAR), IO (Indian-OSCAR), etc. Numbers are assigned sequentially — at time of writing AMSAT has launched satellites with numbers well above 100. The number is allocated to the satellite regardless of whether it is currently operational.