Here’s a video on how to calibrate an MMDVM (Multi Mode Digital Modem) using an RTL-SDR dongle and SDR Sharp as a spectrum analyser.
Haywood Rd. Community Centre,
46 Haywood Rd,
South Notts Amateur Radio Club
c/o Haywood Rd. Community Centre,
Code and framework are © Howard Keene G1GBO (2021)