Multiband WSPR transceiver

Some interesting links on the Weak Signal Propagation Reporter (WSPR) protocol:

Short description

This project implements a standalone multiband WSPR transceiver with all the WSPR signal processing done by STEMlab SDR in the following way:

With this configuration, it is enough to connect STEMlab SDR to an antenna and to a network. After switching STEMlab SDR on, it will automatically start operating as a WSPR receiver.

The transmitter part is disabled by default and should be enabled manually.


The FPGA configuration consists of sixteen identical digital down-converters (DDC). Their structure is shown on the following diagram:

WSPR receiver

The DDC output contains complex 32-bit floating-point data at 375 samples per second and is directly compatible with the WSPR decoder.

The projects/sdr_transceiver_wspr_122_88 directory contains three Tcl files: block_design.tcl, rx.tcl and tx.tcl. The code in these files instantiates, configures and interconnects all the needed IP cores.


The write-c2-files.c program accumulates 42000 samples at 375 samples per second for each of the sixteen bands and saves the samples to sixteen .c2 files.

The recorded .c2 files are processed with the WSPR decoder.

The decoded data are uploaded to using curl.

The script launches write-c2-files, wsprd and curl one after another. This script is run every two minutes by the following cron entry in wspr.cron:

1-59/2 * * * * cd /dev/shm && /media/mmcblk0p1/apps/sdr_transceiver_wspr_122_88/ >> decode-wspr.log 2>&1 &

The transmit-wspr-message.c program transmits WSPR messages.

GPS interface

A GPS module can be used for the time synchronization and for the automatic measurement and correction of the frequency deviation.

The PPS signal should be connected to the pin DIO3_N of the extension connector E1. The UART interface should be connected to the UART pins of the extension connector E2.

The measurement and correction of the frequency deviation is disabled by default and should be enabled by uncommenting the following line in wspr.cron:

1-59/2 * * * * cd /dev/shm && /media/mmcblk0p1/apps/sdr_transceiver_wspr_122_88/ >> update-corr.log 2>&1 &

Getting started

Configuring WSPR receiver

By default, the uploads to are disabled and all the decoded data are accumulated in /dev/shm/ALL_WSPR.TXT.

All the configuration files and scripts can be found in the apps/sdr_transceiver_wspr_122_88 directory on the SD card.

To enable uploads, the CALL and GRID variables should be specified in These variables should be set to the call sign of the receiving station and its 6-character Maidenhead grid locator.

The frequency correction ppm value can be adjusted by editing the corr parameter in write-c2-files.cfg.

The bands list in write-c2-files.cfg contains all the WSPR frequencies. They can be enabled or disabled by uncommenting or by commenting the corresponding lines.

Configuring WSPR transmitter

The WSPR message, transmit frequency and frequency ppm value can be adjusted by editing transmit-wspr-message.cfg.

Building from source

The installation of the development machine is described at this link.

The structure of the source code and of the development chain is described at this link.

Setting up the Vitis and Vivado environment:

source /opt/Xilinx/Vitis/2020.2/

Cloning the source code repository:

git clone
cd red-pitaya-notes

Building sdr_transceiver_wspr_122_88.bit:

make NAME=sdr_transceiver_wspr_122_88 PART=xc7z020clg400-1 bit

Building SD card image zip file:

source helpers/