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.
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?
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.
This seems like a crude way to do it.. why not provide all 110 carrier frequencies by using a polyphase channelizer? The bandwidth of the entire AM broadcast band is pretty low..
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.
> because automatically restarting a transmitter in an unmanned tunnel is not an acceptable failure mode
Why?
Also, surely they don't mean unmanned, who is listening to the AM emergency broadcast then?
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
I'm curious about challenges (what's bad with AM broadcast in an unmanned tunnel?) and why the formally verified killswitch was necessary?
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?
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.
I've also seen these used to add audio to art installations in commuter tunnels.
Thank you, I too was confused at the purpose of this
>NCO: 12 Numerically Controlled Oscillators generate carrier frequencies (505–1605 kHz)
This seems like a crude way to do it.. why not provide all 110 carrier frequencies by using a polyphase channelizer? The bandwidth of the entire AM broadcast band is pretty low..
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.