Ihar Yatsevich's Pocket-Sized WSPR Beacon Uses a SiLabs Si5351 and a Microchip ATmega328
Released under the GPL v3, this open-hardware transmitter handles WSPR now with plans to add CW and FT8 modes in the future.
Developer Ihar Yatsevich has designed a compact device for the radio amateur looking to experiment with WSPR transmission, built around the Silicon Labs Si5351 clock generator and a Microchip ATmega328 microcontroller.
"WSPR (Weak Signal Propagation Reporter) is a digital radio communication protocol developed to study the propagation of weak signals over long distances, allowing radio amateurs to observe in real-time how far radio signals from a specific transmitter can travel," Yatsevich explains. "My interest in WSPR technology began with decoding WSPR messages via a WebSDR receiver, but I had no experience in transmission and wanted to try it."
Yatsevich's first WSPR transmitter was based around the Silicon Labs Si5351 clock generator under control of a NodeMCU Espressif ESP8266 microcontroller. "It work[ed], but poorly," the developer admits. "WSPR messages are successfully transmitted and decoded using a locally positioned SDR [Software-Defined Radio] receiver, but I really dislike breadboard connections when using ready-made modules. As expected, I encountered issues: a poor contact, a slight nudge, and something falls off. Using such a tangle of modules as a finished device is completely impractical."
To resolve this, Yatsevich set about designing a dedicated PCB to house the components — building on an existing design that paired the Si5351 clock generator with a Microchip ATmega328 microcontroller. "[I] added a GPS module and a simple amplifier with a single BS170 field-effect transistor," the developer explains. "To eliminate the frequency drift effect of the Si5351, I installed a TCXO [Temperature-Compensated Crystal Oscillator] instead of the quartz resonator used in ready-made modules."
The finished board, which is installed in an off-the-shelf aluminum chassis for increased robustness, is powered over a USB Type-B connector. SMA connectors provide connectivity for an external GPS antenna and the transmission antenna, with a maximum output power of ~23dBm. While the device is fully-functional, Yatsevich has already detailed a range of planned improvements — including automated calibration, a tuning-free buffer amplifier, and a new firmware that would add CW and FT8 digital modes along with WSPR.
More information on the project is available in Yatsevich's Reddit post, while schematics, Gerbers, and firmware source code are available on GitHub under the reciprocal GNU General Public License 3.