FreeDV: Open Source Amateur Digital Voice – Where Amateur Radio Is Driving The State of the Art
New Digi Modes Changing Complexion of Bands & Perhaps of Ham Radio – M0OXO
Data & Text Mode digital Radio | VU2NSB.com - Amazing Amateur Radio
Great Website to Identify Digital modes by visual and sound clips - YouTube
ARRL General Class License Manual for Ham Radio 9th Edition - Complete Study Guide with Exam Questions for Operating on HF Bands and Digital Modes: ARRL Inc.: 9781625951069: Amazon.com: Books