SDR: Pi Projects - cyberxml/pentos GitHub Wiki

PiFmRds
https://github.com/F5OEO/PiFmRds

Freq Show: Raspberry Pi RTL-SDR Scanner
https://learn.adafruit.com/freq-show-raspberry-pi-rtl-sdr-scanner/overview?embeds=allow

RPi TX Filter
https://hackaday.com/2018/04/03/filter-your-pi-and-be-a-responsible-pirate/
http://naich.net/wordpress/index.php/taming-the-pifm-transmitter-part-2/

WSPR on Pi
http://wsprnet.org/drupal/node/5353

Raspberry Pi SDR with GNURadio
http://www.jacobzelek.com/2016/raspberry-pi-sdr/

Parts

Filters https://www.minicircuits.com/

TX Hats 20m
https://tapr.org/kits_20M-wspr-pi.html
https://hackaday.com/2016/03/16/tiny-raspberry-pi-shield-for-high-quality-rf-signals/

https://www.tindie.com/stores/cburgess129/