SSTV (Slow Scan Television) is a method used by amateur radio operators to transmit still images over radio frequencies. With a low-cost SDR dongle, free decoding software, and a simple antenna, you can receive and decode SSTV pictures from ham radio operators around the world. In this guide, I’ll show you exactly how to set up an SDR for SSTV reception, including recommended frequencies, software, and practical tuning tips.
SSTV is commonly transmitted on HF bands (e.g., 20 meters) for global reach and VHF bands (e.g., 2 meters) for local or space-based signals. Popular modes include Scottie (S1/S2), Martin (M1/M2), Robot (8/12/24/36/72), and PD (90/120/180/240), each varying in resolution and transmission time.
Required Equipment
To get started, you’ll need the following:
Hardware
- SDR Receiver: An RTL-SDR dongle (e.g., RTL-SDR Blog V3 or V4, costing around $20-40). These support frequencies range from about 500 kHz to 1.7 GHz, with modifications or upconverters for lower bands.
- Antenna:
- For VHF (e.g., ISS on 2m band): A simple dipole, quarter-wave vertical, or discone antenna tuned to around 145 MHz. A telescoping dipole in a horizontal V-shape (120° angle, each arm ~50 cm) works well for overhead passes.
- For HF (e.g., 20m or 11m bands): A long wire, dipole, or magnetic loop. If using RTL-SDR for HF below 24 MHz, consider a direct sampling mod or an upconverter.
- Computer: Windows, Linux, or macOS with a USB port. A laptop is ideal for portability.
- Optional: Good coaxial cable (e.g., RG-58) to connect the antenna, and an SMA adapter if needed.
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Software
- SDR Software: To tune and demodulate the signal.
- Windows: SDR# (SDR Sharp), SDRUno, or HDSDR.
- Linux: GQRX or CubicSDR.
- macOS: CubicSDR.
- SSTV Decoder: To interpret the audio into images.
- Windows: MMSSTV (free, supports most modes).
- Linux: QSSTV or RX-SSTV.
- Multi-platform: MultiMode or fldigi (with SSTV plugin).
- Virtual Audio Cable: To pipe audio from the SDR software to the decoder. Options include:
- Windows: VB-Audio Cable (free).
- Linux: PulseAudio (built-in) or JACK.
- Tracking Software (for ISS): GPredict (Linux/multi-platform) or Orbitron (Windows). Alternatively, use websites like Heavens-Above.com for pass predictions.
Install all software before proceeding. For RTL-SDR, ensure drivers like Zadig (Windows) are set up to recognize the dongle.
Step-by-Step Guide
Using a RTL SDR Dongle to receive pictures from the ISS! | Software Defined Radio
1. Prepare Your Setup
- Connect the SDR dongle to your computer and antenna.
- Install and configure the virtual audio cable. In Windows with VB-Cable, set it as the output in the SDR software and the input in the SSTV decoder. On Linux, use pavucontrol to route audio from GQRX’s output to QSSTV’s input monitor.
- Launch your SDR software and test by tuning to a known FM radio station to confirm reception.
2. Find SSTV Activity
- Frequencies:
- VHF: 145.500 MHz FM (calling frequency), 145.800 MHz FM (ISS downlink).
- HF: 14.230 MHz USB (20m band, popular for SSTV), 27 MHz (11m CB band, often in AM).
- Check for activity using online resources like ham radio forums, DX clusters, or apps like HamAlert. For ISS events, monitor ARISS announcements or NASA schedules – transmissions occur a few times a year.
- For ISS: Use tracking software to predict passes. Select passes with at least 10° elevation for better signals. Note the start/end times and azimuth.
3. Tune and Receive the Signal
- Open your SDR software.
- Set the frequency (e.g., 145.800 MHz for ISS) and mode (FM for VHF, USB for HF).
- Adjust gain: Start at 30-40 dB to avoid overload; increase if the signal is weak.
- Enable noise reduction if available (e.g., noise blanker for impulse noise).
- For ISS: Account for Doppler shift – the frequency may vary by ±3-5 kHz as the ISS approaches/recedes. Manually adjust or use auto-tracking if your software supports it.
- Output the demodulated audio to the virtual cable.
4. Decode the SSTV Signal
- Launch the SSTV decoder (e.g., MMSSTV).
- Set the input to the virtual audio cable.
- Select the expected mode (e.g., PD120 for recent ISS events – 640×496 resolution, ~120 seconds per image).
- SSTV signals start with a tone sequence (VIS code) that auto-detects the mode in most software.
- As the signal comes in, the image will build line by line. Enable slant/drift correction if the image skews.
- Save received images automatically in the software settings.
5. Example: Receiving from the ISS
- Use GPredict or Heavens-Above to find a pass.
- Position your antenna outdoors, clear of obstructions, ideally pointing toward the pass direction.
- Start receiving 1-2 minutes before the ISS rises above the horizon.
- Tune to 145.800 MHz FM in a narrow bandwidth.
- Pipe audio to MMSSTV (Windows). Details below…
- Expect 8-12 images per pass, depending on duration.
6. General HF SSTV Reception
- For 14.230 MHz: Use USB mode, bandwidth ~2.5-3 kHz.
- Monitor for signals; transmissions often occur on weekends or during nets.
- If using RTL-SDR for HF, ensure proper setup (e.g., SpyVerter upconverter for clean reception).
📡 Want better reception?
Your antenna matters more than your radio.
To receive SSTV images using MMSSTV, follow these steps to configure your software.
1. Software Configuration
- Setup Audio Devices: Open MMSSTV and navigate to Option > Setup MMSSTV(O).
- Configure Inputs: Under the Misc tab, select the correct input and output sound card devices that correspond to your radio connection.
- Clock Calibration: To ensure images do not appear slanted, verify your sound card settings in the same Misc tab, specifically the “Clock” section. If you encounter consistent slanting, you may need to adjust the clock settings to match your specific hardware.
2. Receiving Images
- Tune the Radio: Tune your receiver to a known SSTV frequency (e.g., 14.230 MHz USB for 20m, or 145.800 MHz FM for ISS passes).
- Set Mode: In the main MMSSTV window, navigate to the RX tab and set the receive mode to Auto. This allows the software to detect the specific SSTV mode being transmitted.
- Adjust Volume: Monitor the audio level in the MMSSTV window.
- The bar should turn green when a signal is present.
- If it is red, your volume is too high (causing distortion).
- If it is gray, no signal is being detected.
- Decoding: Once the signal is locked, MMSSTV will automatically decode the image. If the image appears slanted during or after reception, you can use the Sync tab to apply automatic slant correction.
3. Saving Images
Once an image has been received:
- Navigate to the History tab in MMSSTV.
- Right-click on the desired image to save it. You can choose to save the image with or without an automatic date/time stamp overlay.
Tips and Best Practices
- Antenna Placement: Outdoors and elevated for a better signal-to-noise ratio. For ISS, a northward-pointing V-dipole minimizes ground interference.
- Signal Quality: Weak signals may result in partial images; use higher gain or better antennas.
- Automation: Scripts or tools like rtl_fm can record IQ files for later decoding.
- Legal Notes: No license needed to receive, but transmitting SSTV requires an amateur radio license.
- Communities: Join forums like Reddit’s r/RTLSDR or QRZ.com for schedules and advice.
- Experiment with different modes and software for optimal results.
Troubleshooting
- No Signal: Check antenna connection, gain settings, and pass times. Ensure no local interference (e.g., from Wi-Fi).
- Distorted Images: Adjust audio levels, enable sync correction, or compensate for Doppler.
- Software Crashes: Use compatible versions; test audio routing separately.
- Weak HF Reception: Add a preamp or filter for noise reduction.
- If issues persist, record the audio (e.g., via Audacity) and decode offline.
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