Jun 19, 2025, 11:22 AM

I am happy to announce the release of a longwave software defined radio which I designed at work for experiments with #DSP algorithms, running on the #ULX3S #FPGA board. The user interface is based on #Mecrisp #Forth running on the #FemtoRV, and the signal chain contains a pipelined FFT designed by Dan Gisselquist. Many thanks to Ulixxe for their USB-CDC implementation!

https://github.com/mb-sat/ulx3s-longwave-sdr
https://codeberg.org/Mecrisp/ulx3s-longwave-sdr

Screenshot of the SDR in action, receiving maritime weather service NAVTEX on 147.3 kHz. On top of the image, there is a spectral waterfall display, on the bottom, the IQ components of the signal itself and their Fourier transform are visible.

Hardware setup for the SDR in 1-bit conversion mode. Two USB cables are connected to the ULX3S board, along with a HDMI monitor cable and jumper wires to a small breadboard on which a few passive components for oversampling 1-bit analog-digital conversion using the LVDS comparator of a differential pair. The variable resistor is for setting the DC offset. Two jumper wires leave the image, the orange one carrying signal from the antenna preamp and blue for ground. One could also connect these two wires directly to the FPGA board, using the on-board 12 bit MAX11125 ADC converter.