An extensive literature suggests that anti-regime media stabilizes autocracies. I theorize that mass media can effectively facilitate coordination and protest by tapping into consumers' existing social networks. I evidence this using the case of Radio Free Europe (RFE), which at its peak broadcast daily to over 35 million listeners. Secondarily, I introduce a new method for analyzing satellite and radio signal propagation to the political science literature. To do so, I triangulate across original data sources comprising over 4,000 listener letters, records from more than 1,900 protesters, and a newly digitized survey from 1967. I find that improved signal predicts protester social networks during a major 1968 protest wave, as well as increased community engagement with the station. Together, this study provides a crucial example of how traditional media can serve as a “proto-social media,'' facilitating autocratic opposition via improving audiences' coordination capacity.

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