How Satellite Pass Predictions Work
Amateur radio satellite pass predictions use Two-Line Element sets (TLEs) to calculate exactly where each satellite will be at any future time. The SGP4 propagation algorithm models the satellite's position second by second, while Orbital Radar cross-references each NORAD catalogue entry against the SatNOGS transmitter database to identify which objects carry amateur radio payloads and what frequencies they operate on.
Unlike visual satellite passes, amateur radio passes do not require darkness or twilight — you can work a satellite pass in broad daylight, in rain, or through clouds. The only requirement is that the satellite is above your horizon (typically 10° elevation or higher for a usable signal).
Understanding Doppler Shift
LEO satellites orbit at approximately 7.5 km/s. This velocity causes the received frequency to shift — higher as the satellite approaches, lower as it recedes. The effect is more pronounced at higher frequencies: a 435 MHz downlink shifts by approximately ±10 kHz over a pass, while a 145 MHz signal shifts ±3.5 kHz. For FM satellites, your receiver's bandwidth (typically ±5 kHz) absorbs most of the shift. For SSB and CW operation on linear transponders, you must actively correct for Doppler shift or your signal will drift out of the passband.
The standard practice is to correct on the uplink (your transmit frequency) and leave the downlink constant. This means everyone monitoring the satellite's downlink hears a stable signal from you. Orbital Radar's Doppler gauge computes this correction in real time using the satellite's range-rate derived from SGP4 propagation.
How to Hear the ISS on Ham Radio
The International Space Station is the easiest amateur radio satellite target. Its cross-band FM repeater operates on 145.800 MHz downlink and 145.990 MHz uplink. Even a basic handheld radio with a whip antenna can receive ISS signals during a high pass. For your first attempt, simply tune to 145.800 MHz and listen during a pass above 30° elevation — you'll hear other operators making contacts through the repeater. The ISS also runs an APRS digipeater on 145.825 MHz and occasionally transmits SSTV images.
Getting Started: Equipment Guide
Key Amateur Radio Satellites
As of mid-2026, there are approximately 80–120 active satellites carrying amateur radio transponders or beacons. The most popular targets include the ISS (cross-band FM repeater and APRS digipeater), SO-50 (SaudiSat-1C, one of the longest-running FM satellites as of 2026), FO-29 (Fuji-OSCAR 29, an SSB/CW linear transponder), and the TEVEL constellation of FM CubeSats. The geostationary transponder QO-100 (Es'hail-2) provides continuous coverage for operators in its footprint across Europe, Africa and Asia. Check the pass list above for current operational status of each satellite.
OSCAR Satellite Tracker & Pass Predictions
This tool serves as a comprehensive OSCAR satellite tracker, computing pass predictions for every active amateur radio satellite in real time. Unlike static pass tables, our predictions update continuously using fresh TLE orbital elements from Space-Track and transmitter data from SatNOGS. Each pass card shows the satellite's trajectory across your sky, the optimal pointing direction for your antenna, and — uniquely — live Doppler-corrected frequencies so you can tune your radio with confidence.
Making a Contact (QSO)
Satellite QSOs are brief by necessity — a pass typically lasts 5–15 minutes and is shared by many operators. The standard exchange on FM satellites is callsign and grid square. On SSB/CW, you can exchange signal reports (RS/RST) as well. Keep transmissions short, use the minimum power necessary (5W is typically sufficient for LEO FM), and always listen before transmitting to avoid doubling.
Radio propagation is directly affected by space weather — solar flux and geomagnetic storms can enhance or degrade VHF/UHF signals. Check the space weather indicator above the pass list for current conditions. For more orbital mechanics context, visit the Orbital Academy. To track specific satellites in 3D, use the live globe. Browse all tracked objects in the satellite directory, explore satellites by country, or browse the full Space Library with 175+ reference pages covering everything in orbit.