This reminds me of stories about coded messages during World War II [1]. This could be used to maybe embed data messages within public broadcasts? I wonder how

This reminds me of stories about coded messages during World War II [1]. This could be used to maybe embed data messages within public broadcasts? I wonder how much data quality could degrade over AM/FM modulations. There is of course packet radio for data transmissions, but I am specifically thinking about public broadcast. A scenario I thought of is a broadcast in distressed areas, similar to the WWII coded messages, but with addition of data layer embedded that could authenticate the authenticity of the messages, for example. [1] https://en.wikipedia.org/wiki/Radio_Londres https://en.wikipedia.org/wiki/Radio_Londres