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.
Thank you, I too was confused at the purpose of this
_moof•47m ago
I've also seen these used to add audio to art installations in commuter tunnels.
jasonjayr•23m ago
I'm curious about challenges (what's bad with AM broadcast in an unmanned tunnel?) and why the formally verified killswitch was necessary?
meindnoch•5m ago
A tunnel basically acts as a waveguide. A sufficiently shaped AM transmission can turn the tunnel into a cavity resonator, basically a huge microwave oven. There have been multiple cases where people were cooked alive in mines and utility tunnels, due to faulty AM equipment broadcasting at the wrong resonant frequency.
davepage•41m ago
Could obtain better quality at the higher channel counts by phase shifting the audio for each channel such that the modulation peaks do not exactly align for each (as they do now). Even inverting the audio for half the channels would help.
jetrink•1h ago
https://en.wikipedia.org/wiki/Leaky_feeder
cbdevidal•1h ago
_moof•47m ago
jasonjayr•23m ago
meindnoch•5m ago