Receive pictures and packets from the ISS: SSTV and APRS for beginners
During ARISS events the space station sends slow-scan TV pictures anyone can decode, and its packet radio relays short messages from the ground. What you need, which frequency to use now, and how to turn the sounds into an image.
A picture sent from orbit, straight to you
Several times a year the ARISS team (Amateur Radio on the International Space Station) runs a slow-scan television event. For a few days the station's radio sends a series of themed pictures, one after another, and anyone under the station can catch them with a scanner, a handheld radio or a cheap SDR.
Slow-scan TV, or SSTV, turns an image into a string of audio tones. Each tone stands for a brightness, and the picture is painted line by line as the sound plays. Decoding software on a computer or phone listens to the audio and rebuilds the image as it arrives. The first time you watch a picture of the station appear from a noise that came from 400 km overhead is hard to forget.
Which frequency and mode, right now
This has changed over the years, so check before each event. Recent events in 2026 have been sent on 437.550 MHz FM in the Robot36 mode, which takes about 36 seconds per picture. Older events used 145.800 MHz FM and the PD120 mode, about two minutes per picture, and some events may still use that.
Every event is announced in advance on ariss.org and by AMSAT, with dates, frequency and mode. Our ISS radar lists the station's current transmitters and shows each frequency corrected for Doppler during the pass.
What you need
- A receiver for the band: an RTL-SDR dongle, a scanner, or any FM handheld that covers 145 or 435 MHz.
- An antenna. For a high pass the radio's own antenna can work; a small handheld Yagi or a simple ground plane cut for the band makes a big difference.
- Decoding software: MMSSTV (Windows), QSSTV (Linux), or the free Robot36 app (Android). On a phone, the app can simply listen to the radio's speaker.
- A pass time for your location, ideally one that climbs above 30°.
Catching your first picture
Start listening a minute before the station rises. At 437.550 MHz the Doppler shift is up to about 10 kHz, so a narrow FM signal can slide out of the receiver's passband: begin about 10 kHz above the frequency and step down through the pass (437.560, 437.555, 437.550, 437.545, 437.540), or let your SDR software track it.
Set the decoder to the event's mode, or to automatic mode detection. Keep the volume moderate: overdriven audio produces streaks. When the sound starts, the image builds from the top. Noise shows as speckles, and a short dropout leaves a band across the picture. Both are normal, and many people stitch the best parts of two passes together.
After an event, ARISS usually invites listeners to upload their pictures to its SSTV gallery and offers a certificate for reception reports.
APRS: the station as a mailbox in the sky
Between events the station's radio often runs as a packet digipeater. Ground stations send short APRS packets (a call sign, a position, a few words), the station relays them, and everyone in its footprint can hear them. The classic frequency is 145.825 MHz at 1200 baud; at times the packet system has also been tested on 437.825 MHz, so check the radar's radio list.
To decode packets, feed the receiver's audio to Direwolf on a computer, or use APRSdroid on Android. You will see call signs and positions from stations across a whole continent, all heard in the few minutes the station is overhead. Transmitting needs an amateur licence; listening does not.
When it doesn't work
Check, in order: is an event actually running (SSTV is not continuous); is the station above about 15° for most of the pass; is the receiver on the current frequency and following the Doppler shift; and is the decoder hearing clean audio, not a hiss from too much squelch or a mode mismatch. Recording the audio lets you decode it again later with other settings.