DATV TX Tutorial

This community guide uses GNU Radio Companion to encode a video as a DVB-S2 signal and sends the IQ output to SimTX. DATV means digital amateur television. Complete Getting Started first; a normal audio-file transmission is a simpler way to check account and server access.

Software and example files

• GNU Radio Companion. The original guide linked a Windows radioconda installer; use the radioconda project for current installers.
• FFmpeg builds for preparing the video.
• Mukhash2012's DVB-S2 flowgraph and SimTX preset. Keep both files together for reference.
• A receiver setup from DATV RX Tutorial for checking the result.

1. Prepare the video

The original example converts an MP4 to an MPEG transport stream with low-rate H.264 video and mono AAC audio. Replace the input and output filenames with your own. This preserves the settings supplied by the original tutorial.

ffmpeg -i File_name.mp4 -c:v libx264 -b:v 85k -maxrate:v 85k -bufsize:v 30k -preset slow -profile:v baseline -level 3.0 -vf "scale=320:240,fps=12,format=yuv420p" -c:a aac -b:a 24k -ac 1 -f mpegts -muxrate 140k -mpegts_pmt_start_pid 0x1000 -mpegts_start_pid 0x0100 -pcr_period 20 -pat_period 0.1 File_name.ts

2. Configure GNU Radio and SimTX

1. Open the supplied .grc flowgraph in GNU Radio Companion.
2. Open its File Source block and select the converted .ts file. A File Source reads the video; a File Sink writes an output file.
3. Check the flowgraph's TCP Sink. In the illustrated setup it is a client connecting to 127.0.0.1, port 7355.
4. In SimTX, use Presets > Load Preset File... to load the supplied .stxpreset.
5. Review the preset's station, frequency, power, and antenna. Confirm GNU Radio IQ is selected, its IQ Port matches the TCP Sink, and the expected sample rate matches the flowgraph.

The original flowgraph illustration. It shows a 200000 samples/s output, 100000 symbols/s, QPSK, and code rate 3/4. Current downloaded files should be checked rather than assumed identical.

3. Start and verify

1. Start the SimTX transmission first so its local IQ input is listening.
2. Run the GNU Radio flowgraph so the TCP Sink connects to it.
3. Use DATV RX Tutorial with matching DVB-S2 parameters to check reception.

The illustrated parameters are one example, not settings for every DATV station. If no picture appears, check TCP connectivity first, then sample rate, symbol rate, code rate, receiver frequency, and signal strength. Stop the SimTX session when the test is finished.