Working Amateur Satellites: FM Repeater Sats, ISS APRS, and Doppler Tuning

If you've already got a ham license and a shortwave receiver like the ATS Mini V4 or an RTL-SDR dongle on your bench, working satellites is a natural next step — and it's a surprisingly accessible one. You don't need a satellite dish or a tracking mount that costs more than your car. A large chunk of amateur radio satellite activity happens on simple FM repeaters you can work with a $30 handheld radio and a homemade antenna, and the International Space Station itself regularly transmits slow-scan television images that anyone with a basic VHF receiver can decode. This guide covers the gear, the software, and the technique for working your first pass.

What's Actually Up There

Satellite TypeExamplesModeDifficulty FM "easy sats"SO-50, AO-91, AO-92FM voice, single uplink/downlink pairBeginner ISS SSTV eventsISS (scheduled events, several times a year)Slow-scan TV image transmission on 145.800 MHz FMBeginner (receive only) ISS APRS digipeaterISSAPRS packet on 145.825 MHzBeginner–intermediate Linear transponder satsAO-7, FO-29, RS-44SSB/CW, full-duplex listen-while-you-transmitIntermediate Digital/high-speed satsVarious CubeSatsVarious digital protocols, often receive-only for hobbyistsAdvanced

Gear You Need to Start

For your very first pass, you can get away with remarkably little: a dual-band (2m/70cm) HT, a simple handheld directional antenna like an Arrow or an Elk log-periodic, and a printed or app-based pass schedule. Nothing here needs to be expensive — the antenna matters far more than the radio for a first FM satellite contact, since you're working with a satellite whose downlink is often stronger than a terrestrial repeater's. If you'd rather start receive-only before you transmit, an RTL-SDR or the ATS Mini V4 tuned to 145.800 MHz will let you pull in ISS SSTV images with zero risk of a bad transmission, which is a good low-pressure way to learn pass timing before you try a two-way FM contact.

Predicting and Tracking a Pass

Free tools like Gpredict (desktop, Linux/Mac/Windows) or Look4Sat and Heavens-Above (mobile/web) pull current orbital elements (TLEs) and calculate exactly when a given satellite will rise above your horizon, its maximum elevation, and its azimuth path across the sky. Elevation matters more than most beginners expect — a pass that only reaches 10–15 degrees above the horizon will be short and noisy with obstructions, while a pass reaching 60-plus degrees overhead gives you several clean minutes of strong signal. Pick a high-elevation pass for your first attempt.

Doppler Shift and How to Handle It

Satellites in low Earth orbit move at roughly 7.5 km/s relative to the ground, which shifts the received frequency by several kHz as the satellite approaches, passes overhead, and recedes — enough to walk a signal clean off a narrow FM channel over the course of a pass if you don't compensate. For FM satellites, the standard approach is to step your receive frequency down in a few discrete increments as the pass progresses (satellite tracking apps will tell you the current Doppler-corrected frequency in real time, or publish a simple staged schedule: start a few kHz high, then work your way down as the pass crosses overhead). For linear-transponder satellites, both your transmit and receive frequency shift independently and need continuous small adjustments — full-duplex operation, listening to your own downlink signal while you transmit, is what lets you actually hear and correct for this in real time, which is why linear-sat work is considered a step up from simple FM contacts.

Working Your First FM Pass

Confirm the satellite's uplink/downlink frequencies and tone requirements (most FM sats require a specific CTCSS tone on your uplink) from a current satellite frequency reference — these details occasionally change as satellites are reconfigured.
Point your antenna at the horizon where the pass will rise, and start listening a minute or two early — you'll often hear the satellite's downlink before it's officially "above the horizon" per your prediction software's minimum elevation cutoff.
Listen for an opening in the traffic, then transmit your callsign and grid square, keeping transmissions short — FM sat passes are busy, and courtesy matters since everyone in the footprint shares the same single channel.
Track the satellite across the sky by hand with your directional antenna as it moves, and step down your receive frequency as needed to follow the Doppler shift.
Log your contact — many satellite operators use these for satellite-specific achievement awards, and logging is how you build a record for eQSL or LoTW confirmation later.

ISS APRS and SSTV: Two Different Ways the Station Talks Back

The ISS runs two separate amateur radio services worth knowing apart. Its APRS digipeater on 145.825 MHz relays position and short text packets from ground stations back down over a wide footprint, and working it is genuinely satellite operation — track the pass, key up during your window, and watch for your packet to digipeat back. Separately, several times a year the station runs scheduled SSTV events, transmitting still images as audio tones on 145.800 MHz FM. SSTV reception is receive-only and doesn't require tracking a moving target the way APRS or a two-way FM contact does, and we cover the decoding software and step-by-step process for it in detail in our dedicated SSTV guide — if a scheduled ISS SSTV event is what brought you here, start there instead; this guide's focus is on tracking and working satellites as moving targets, which is a different skill from SSTV decoding.

Licensing and Legal Notes

In the US, satellite operation is covered under your existing amateur license class — Technician class already grants you full FM satellite privileges on the VHF/UHF bands most easy sats use, while linear transponder satellites typically require HF/SSB privileges that come with General class. Reception is legal for anyone regardless of license status; transmission requires a valid amateur license and, as with any ham operation, correct identification and adherence to your license class's band and mode privileges. If you're not yet licensed, see our amateur radio license guide — Technician class alone is enough to get you working your first FM satellite pass.

Satellite work is one of the more genuinely magical corners of the ham radio hobby — a low-cost handheld radio and a homemade antenna are all it takes to have a two-way conversation bounced off a spacecraft passing a few hundred kilometers overhead. If you want a completely risk-free first step, spend a pass or two just listening and tracking with prediction software before you ever transmit, then work your way up to a full-duplex FM contact once you're comfortable predicting and tracking a pass by ear and by antenna heading.

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