Blog

📡 TinyWSPR – Generating Shortwave Signals on Open-Source Silicon

Map of WSPR-Propagation over Europe. Logos of Universities, Chip-Foto of Digital and Analog Design.

Weak Signal Propagation Reporter (WSPR, pronounced “whisper”) is a well-known tool in amateur radio for analyzing the propagation of shortwave signals. These signals are refracted by the ionosphere, allowing them to travel remarkable distances around the globe, even with just small transmit powers of just a few milliwatts. The tool, developed by Nobel laureate Joe Taylor (K1JT), typically requires a PC running dedicated software and a shortwave transmitter. While numerous embedded implementations have been created in the past—using microcontrollers or FPGAs—there has so far been no integrated circuit that provides native WSPR functionality.

Until now! In a collaboration between JKU Linz (Simon Dorrer, OE3SDE and Harald Pretl) and the Julius-Maximilians-Universität Würzburg (Jonathan Hager, DK7JH, and myself, DL9MJ), we have implemented a fully WSPR-capable transmitter in the TT-Sky25b process—realized as a 130 nm analog mixed-signal design via Tiny Tapeout. The design consists of two major components: a digital subsystem that generates the transmit symbols from the message information (operator callsign, power level, and location), and an analog subsystem that performs the actual RF modulation. The digital part uses a CORDIC IP block and a sigma-delta modulator to produce a complex analog baseband signal. This signal is then modulated by an IQ-Modulator, filtered, and amplified by a fully analog RF chain.

Now we simply have to wait for the chip to return from the fab before we can finally take it on the air. In the meantime, we have prototyped several of the chip’s IP blocks on FPGAs, and the results are remarkable: with only ~10 mW of transmit power, our signal can be received across central Europe on the 40 m amateur band. Once the fabricated TinyTapeout chip arrives, we will conduct the first on-air transmission tests.