The Spectrum Monitor – DRM-free radio listening magazine

[I'm not an employee, just a radio buff]

If you've ever listened to shortwave radio via the stations at websdr.org, The Spectrum Monitor covers topics like ham radio, pirate radio, scanners, numbers stations, and the like. Not too expensive, and each issue is a plain-PDF file--no DRM.

The current December 2019 issue has a piece on the history of broadcast radio in the U.S. before 1921, when the first broadcast licenses were first issued. Another article examines the U.S. Air Force HFGCS global shortwave communications network, formalized after 9/11 when U.S. military comms satellites were swamped with traffic.