Spectrum Painter transmits an image or text in a way that makes it visible as a pattern on a waterfall display. The image or text is encoded as the instantaneous frequency of the signal over time, painting each row of pixels as a horizontal line in the spectrum.
The app has two tabs: Image and Text.
Controls (common to both tabs)
- Frequency — Center frequency of the transmission.
- GAIN — TX gain, 0–47 dB. Default: 47.
- A: — RF amplifier, 0 or 14 dB. Default: off (0).
- Loop (checkbox, default: on) — Repeats the transmission continuously. When active, the Pause field sets a gap between repetitions.
- BW — Transmission bandwidth. This determines how wide the painted spectrum appears. Options: 12k5, 16k, 25k, 32k, 50k, 75k, 100k (good starting point), 150k, 250k, 500k, 600k, 750k, 1000k, 1250k, 1500k, 1750k, 2000k, 2250k, 2500k, 3000k. Default: 12k5. For visible results on a multi-MHz waterfall span, use at least 500k–2000k.
- Du: — Duration of each transmission in seconds (1–999). Default: 10.
- P: — Pause between transmissions in seconds when Loop is active (0–99). Default: 5.
- ▶ / ■ — Start or stop transmission. A progress bar shows the current position within the transmission.
The internal baseband bandwidth is fixed at 1.75 MHz regardless of the BW setting.
Image Tab
Place .BMP files in the SPECTRUM/ directory on the SD card. Press the file selector to choose a file — a scaled preview is shown on screen before transmission. The selected file is transmitted row by row, with each pixel row becoming one horizontal line in the spectrum.
Supported formats: 16-bit, 24-bit, and 32-bit uncompressed BMP (no compression, single plane). All three bit depths are fully supported.
For best results, use a high horizontal resolution. A width of 2048 pixels works well. Using a power of 2 for the width (512, 1024, 2048, …) gives optimal results.
Text Tab
Enter text using the Set message button (opens the keyboard). The message is displayed across up to 10 lines of 30 characters each on screen. Maximum message length is 300 characters.
Settings Persistence
Settings are saved to tx_painter.ini.