[jetrink]

At first I thought the "unmanned tunnels" description was just a way to avoid broadcast regulator scrutiny, but it does look like it's genuinely designed to be used underground as part of an emergency alert system. That led me to "leaky feeders", a type of broadcast antenna used in mines and tunnels.

https://en.wikipedia.org/wiki/Leaky_feeder

[jasonjayr]

I'm curious about challenges (what's bad with AM broadcast in an unmanned tunnel?) and why the formally verified killswitch was necessary?

[mech422]

I must be missing something ... Why broadcast speech over AM in an 'unmanned' tunnel ?? who's gonna hear/receive it ?? I wish the repo had some sort of use case summary or something...

Edit: I'm also sorta puzzled by the choice of AM in any sort of 'alert' context...Do people still listen to/use AM radios?

[anonymoosestdnt]

Updated the README with a use case section - vehicles with AM radios transit during construction/maintenance. Leaky feeder distributes the signal. Thanks for the feedback :)

[jacquesm]

AM radios are extremely simple and utterly fool proof, they can be made with only a handful of simple parts. Even so, these systems are archaic and these days you can make much more complex radio systems using a SDR which effectively reduces the whole radio to a pre-amp an ADC, an embedded CPU and some software.

[drweevil]

AM is a good modulation choice for low signal environments. It is used in the airbands for this reason.

[jacquesm]

Precisely, it degrades very gracefully, unlike FM or digital.

[_moof]

I've also seen these used to add audio to art installations in commuter tunnels.

[cbdevidal]

Thank you, I too was confused at the purpose of this