Contacting the ISS via Amateur Radio

Some crew members aboard the International Space Station (ISS) occasionally make random, unscheduled amateur radio voice contacts with Earth-bound radio amateur operators. These contacts typically occur during crew breaks, pre-sleep time, and before or after meals. Over the years, astronauts have contacted thousands of hams worldwide.

There are three primary methods for making contact with the ISS:

  1. FM Voice
  2. Slow-Scan Television (SSTV)
  3. APRS Packet Radio

Working FM Voice Contacts

Frequency

  • Downlink (RX): 145.800 MHz FM
  • Uplink (TX): 145.200 MHz FM

When astronauts make a general call (CQ), they transmit on 145.800 MHz FM but listen for replies 600 kHz lower on 145.200 MHz FM. If you hear them calling CQ, activate your rig’s repeater shift to ensure you transmit on the correct frequency. Never transmit on 145.800 MHz.

Best Times for Contact

  • Weekdays: 07:30 – 08:30 UTC, 18:30 – 19:30 UTC
  • Weekends: 07:30 – 19:30 UTC

The ISS crew's usual waking period is 07:30 – 19:30 UTC. Your best chances of making contact are:

  • One hour after crew wake-up
  • One hour before crew bedtime
  • Random times on weekends, when astronauts may have free time

Call Signs Used on the ISS

When making voice contact, use the appropriate ISS call sign based on the location of the operator:

  • Russia: RS0ISS
  • USA: NA1SS
  • Europe: DP0ISS, OR4ISS, IR0ISS

Key Considerations

Radio Equipment

  • A dual-band VHF/UHF transceiver capable of full-duplex operation is recommended.
  • Ensure your rig has a repeater shift function to adjust for split frequencies.

Antenna

  • A directional (Yagi) antenna improves your chances, but a good vertical antenna can also work.
  • A rotatable or hand-held Yagi allows you to track the ISS more effectively.

Doppler Shift

Since the ISS travels at over 28,000 km/h (17,500 mph), radio signals shift in frequency due to the Doppler effect:

  • As the ISS approaches, the downlink frequency appears higher than 145.800 MHz (around 145.8035 MHz).
  • As the ISS moves away, the frequency shifts lower (down to 145.7965 MHz).
  • To adjust for Doppler shift, use a radio that tunes in 1 kHz or smaller steps. However, acceptable results can be achieved by leaving your radio set at 145.800 MHz FM.

Working Slow-Scan Television (SSTV)

The ISS occasionally transmits SSTV images as part of educational and commemorative events. These images can be received by hams and decoded using appropriate software.

Frequency

  • 145.800 MHz FM (Downlink only)

Receiving SSTV Signals

  1. Use an FM receiver tuned to 145.800 MHz.
  2. Connect your radio's audio output to a computer or smartphone running SSTV decoding software, such as:
    • MMSSTV (Windows)
    • RX-SSTV (Windows)
    • Robot36 (Android)
  3. The ISS typically uses PD120 mode for transmissions.

Best Times for SSTV Reception

SSTV events are pre-scheduled and announced by ARISS (Amateur Radio on the ISS). Check their website for upcoming transmissions.

Working APRS Packet Radio

The ISS is equipped with an Automatic Packet Reporting System (APRS) digipeater that allows hams to send and receive short messages and position reports.

Frequency

  • 145.825 MHz FM (Worldwide)

How to Use APRS with the ISS

  1. Set your radio and TNC (Terminal Node Controller) to 145.825 MHz FM.
  2. Use unproto path via ARISS.
  3. Send APRS messages and beacons as you would for terrestrial APRS.
  4. If the ISS digipeater relays your message, it will be received by APRS stations worldwide.
  • APRS-capable transceiver (such as Kenwood TH-D74, TM-D710, or Icom IC-9700).
  • A standard FM radio with an external TNC or software-based modem (such as DireWolf).
  • A good omnidirectional or small Yagi antenna for improved reception.

Additional Resources

For more information on contacting the ISS and amateur satellite communication, check out these resources: