Building radio networks underground?
Or building underground radio networks - as in covert, rather than covered in earth.
Attention radio boffins: hankering for a look at some vivacious valves? Have some ideas on what "could have been" had Britain gotten its hands on certain broadcasting tech just THAT much sooner? There's a wireless heritage special interest group at Cambridge Wireless with plenty of hot models to ponder from the past "100 years …
see the Radio Museum
Unfortunately Regulators like Ofcom & Comreg, Set makers and even the Broadcasters (esp. ones like BBC & RTE with DAB) are trying to kill Radio.
Digital TV is a good idea and reasonably implemented. Inherently ANY digital Radio system is a poorer User Interface than AM or FM. User Power consumption, Mobile/Portable coverage issues etc. DAB isn't the real problem, though not enough transmitters, only suits National Broadcasters and needs twice as many Mux to have decent bitrate.