Receiving ISS SSTV Images

Receiving SSTV images from the GCARC SatNOGS site uses recorded satellite audio files (typically .ogg format) from their ground station observations. You download the audio, play it through Audacity (routed via a virtual audio cable), and decode the Slow Scan Television (SSTV) signal in real time with MMSSTV software. This method works offline after downloading the file and produces high-quality decoded images, especially useful for ISS SSTV events or other satellites captured by the station.

The GCARC (Gloucester County Amateur Radio Club) SatNOGS station is publicly accessible and often records SSTV transmissions (e.g., from the ISS). No radio hardware is needed—just your computer, the free software below, and an internet connection to download the audio files.

1. GCARC SatNOGS Site (Audio Source)

  • Description: This is the web-based observation page for SatNOGS ground station #223 (W2MMD / GCARC Clubhouse in Mullica Hill, NJ). SatNOGS stations record satellite passes and upload lossless audio files (.ogg format) along with waterfall plots. You browse past observations, filter for SSTV-mode passes (e.g., ISS SSTV events), and download the raw audio to decode locally.
  • How to access:
    1. Go to the station page: https://network.satnogs.org/stations/223/
    2. Click the Observations tab (or go directly to the network observations and filter by station 223 and mode SSTV).
    3. Find a relevant observation (look for ones with “SSTV” in the description or strong waterfall signals during known events like ISS SSTV).
    4. On the observation page, click the download icon for the audio file (named something like satnogs_XXXXXX.ogg). Save it to your computer.
  • Tip: SSTV audio is usually in the 145.800 MHz range for ISS. The .ogg files play fine in most software; no conversion is required for this method.

2. Virtual Audio Cable (VB-Audio VB-CABLE)

  • Description: Free software that creates a virtual audio loopback device on your PC. It lets you route audio output from one program (Audacity playing the .ogg file) directly into the input of another program (MMSSTV) without using speakers or physical cables. This enables clean, real-time decoding with no loss.
  • How to download:
    1. Go to the official VB-Audio site: https://vb-audio.com/Cable/
    2. Scroll to the download section and click the latest VBCABLE_Driver_PackXX.zip (e.g., VBCABLE_Driver_Pack45.zip – about 1.3 MB, supports Windows XP to Windows 11, 32/64-bit and Arm64).
  • How to install and set up:
    1. Extract the ZIP file.
    2. Right-click VBCable_Setup.exe (or the setup file) and select Run as administrator.
    3. Follow the installer prompts and reboot your computer when finished.
    4. After reboot, open Windows Sound settings (right-click speaker icon → Sounds or Sound settings):
      • You will now see two new devices:
        • CABLE Input (VB-Audio Virtual Cable) – Use this as the output/playback device for Audacity.
        • CABLE Output (VB-Audio Virtual Cable) – Use this as the input/recording device for MMSSTV.
    5. (Optional but recommended) Set the cable volume to 100% in the Windows Volume Mixer to avoid low signal levels.

3. Audacity (Audio Player)

  • Description: Free, open-source, cross-platform audio editor and recorder. Here you open the downloaded SatNOGS .ogg file, adjust playback if needed (e.g., trim to the SSTV portion), and send the audio through the virtual cable.
  • How to download:
    1. Go to the official Audacity website: https://www.audacityteam.org/download/
    2. Click Download Audacity (current version is around 3.7.x). Choose the Windows installer (avoid third-party sites).
  • How to install and set up:
    1. Run the downloaded installer (.exe) and follow the prompts (no special options needed).
    2. Launch Audacity.
    3. Go to Edit → Preferences → Devices (or use the device dropdowns in the main toolbar).
      • Set Playback Device to CABLE Input (VB-Audio Virtual Cable).
      • (Input device doesn’t matter for playback.)
    4. Open your downloaded SatNOGS .ogg file: File → Open.
    5. (Optional optimization) If the audio is very long, use the selection tool to highlight just the SSTV transmission portion (visible as the characteristic SSTV tones in the waveform). You can also check the sample rate (Edit → Preferences → Quality); 44100 Hz or 48000 Hz works fine.

4. MMSSTV (SSTV Decoder)

  • Description: Free Windows software specifically designed for Slow Scan Television (SSTV). It decodes audio signals into color images in real time. It supports all common SSTV modes (Scottie, Martin, PD120, etc.) and has an automatic mode detector.
  • How to download:
    1. Go to the official HamSoft page: https://hamsoft.ca/pages/mmsstv.php
    2. Download MMSSTV113A.exe (full version, ~2.5 MB, last updated 2010 but still the standard and fully functional for amateur use).
    3. (Optional modern fork) A community-updated version called MMSSTV-YONIQ is also available on the same site or at radiogalena.es/yoniq if you prefer a refreshed interface.
  • How to install and set up:
    1. Run the .exe file and follow the installer (it’s straightforward).
    2. Launch MMSSTV.
    3. Go to Option → Setup MMSSTV (O)…
    4. In the Sound Card or Miscellaneous tab:
      • Set Sound Input (or RX sound card input) to CABLE Output (VB-Audio Virtual Cable).
      • Leave other settings at defaults initially.
    5. In the main MMSSTV window:
      • Set RX Mode to Auto (recommended for ISS SSTV, which often uses PD120 or similar).
      • Enable the waterfall/spectrogram view if desired (it helps visualize the signal).
      • Adjust the Volume slider (green bar) so the signal level peaks nicely without clipping (watch the level meter).

Full Step-by-Step Process to Decode an SSTV Image

  1. Download the .ogg audio file from a GCARC SatNOGS observation as described above.
  2. Make sure VB-CABLE is installed and your PC is rebooted.
  3. Open the .ogg in Audacity and set its Playback Device to CABLE Input (VB-Audio Virtual Cable).
  4. Open MMSSTV and set its Sound Input to CABLE Output (VB-Audio Virtual Cable). Set RX mode to Auto.
  5. In Audacity, press the Play button (spacebar or play icon). Start from the beginning of the SSTV tones (you’ll hear the characteristic “beeps” and tones).
  6. Watch MMSSTV: The signal should appear in the frequency graph/waterfall, and decoding will begin automatically. Images build line-by-line in the RX window.
  7. When finished, you can save the decoded image via File → Save Picture in MMSSTV.
  8. (Troubleshooting tips)
    • No signal in MMSSTV: Double-check device selections and cable volumes. Try restarting both programs.
    • Distorted/poor decode: In Audacity, resample the track (Tracks → Resample) to 11025 Hz or 48000 Hz if needed, then re-export temporarily as WAV if direct playback fails.
    • Low volume: Increase the CABLE volume in Windows Sound settings or Audacity playback level.
    • Mode mismatch: Manually select the known SSTV mode (e.g., PD120 for recent ISS events) instead of Auto.

This setup is reliable, widely used by the amateur radio community for replaying SatNOGS recordings, and completely free. Once you have it working with one file, you can decode any SSTV observation from the GCARC station (or any other SatNOGS station) instantly. Enjoy the space pictures!

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