[HN Gopher] Show HN: Formally verified FPGA watchdog for AM broa...
___________________________________________________________________
Show HN: Formally verified FPGA watchdog for AM broadcast in
unmanned tunnels
Author : anonymoosestdnt
Score : 53 points
Date : 2026-02-18 15:06 UTC (7 hours ago)
(HTM) web link (github.com)
(TXT) w3m dump (github.com)
| jetrink wrote:
| 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
| cbdevidal wrote:
| Thank you, I too was confused at the purpose of this
| _moof wrote:
| I've also seen these used to add audio to art installations in
| commuter tunnels.
| jasonjayr wrote:
| I'm curious about challenges (what's bad with AM broadcast in
| an unmanned tunnel?) and why the formally verified killswitch
| was necessary?
| mech422 wrote:
| 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?
| jacquesm wrote:
| 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.
| davepage wrote:
| 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.
| westurner wrote:
| I happened to find a video about how the Osireon in Egypt is
| similar to structures constructed within Longyou caves. They are
| historically contemporary and they are separated by a multiple of
| 72 degrees. Angkor Wat and (TODO a number of other ancient
| facilities) perhaps coincidentally are also on a geographic
| pentagon at 72deg degrees.
|
| Unfortunately, due to TODO some sort of procession you would
| expect such a LF/VLF comm net to be off by about 1deg after 72
| years though? Perhaps this is part of why they built new temples
| etc. adjacent to older sites. The Temple of Seti is built
| adjacent to the Osireon, for example.
|
| Anyways, the scalloped marks on the walls of Longyou caves very
| likely operate as LF/VLF diffusers for local and far away signals
| that propagate TTE Through-the-Earth and also through water and
| hydrogen.
|
| At 21cm, the northern Star Shaft in the Great Pyramid waveguides
| 1420 MHz. 1420 MHz is the fundamental frequency of Hydrogen.
|
| The star shaft contain 0.25" copper rods that would have been
| deoxidized by hydrogen. The star shafts were enclosed. People
| have speculated that they were for ventilation, but the star
| shafts were found sealed with the oxidized copper rods inside.
|
| That copper could have been from the Great Lakes back then.
|
| Why would you add copper rods to the tallest structure around in
| the desert, in shafts that would accumulate hydrogen if the
| structure was filled with water that foams as it drains out?
|
| Are those antennae and/or ionospheric and/or _lightning_ charge
| collectors to charge the granite and discharge to make plasma in
| a 6,000 ton pressure vessel?
|
| Is that an above ground cave? An above ground cave that makes:
| (0) ionized Water sanitized with hydrogen plasma and solar
| sanitized water, (1) Gold and Neodymium from SPP Surface Plasmon
| Polaritons in quartzite sand in electrified hydrogen plasma, (2)
| Doped A-CNT Carbon Nanotubes that glow blue in the presence of
| hydrogen and Diamond (3), and RF and EMF? Wouldn't it have been a
| beacon on multiple frequencies?
|
| Anyways,
|
| The pressure vessels found in Egypt - for example with a pyramid
| built around it at Saqqara - very likely resonate tuned LF
| resonance.
|
| The pressure vessels may resonate a source signal that would
| stabilize hydrogen being slowly emitted to cool a quantum locked
| floating barge that could have made it easier to transport and
| place 100 ton granite blocks from a quarry miles away.
|
| Also though, there are a number of hypotheses about pyramid
| construction that do not involve levitation or quantum locking of
| a depressurizing hydrogen vessel over neodymium - and maybe gold
| for corrosion - tracks or rails. Stephen Myers, for example,
| describes placing stones with barge cranes floating in a pool
| bounded by casing stones first. The Grand gallery (todo) does
| appear to be shaped like a water lock and there was no ladder or
| railing. And there are redundant portcullis doors. But the math
| to move a 100 ton stone without crushing wooden barges.
|
| ...
|
| LoRA will work better than AM in a cave.
|
| There are AM dead zones in caves. Scalloped walls that diffuse
| like Longyou caves can probably reduce those dead zones.
|
| It looks like modern TTE systems are also built on VLF/LF.
|
| Receiver cost for AM vs LoRa; but range? And then why not LF/VLF?
| hersko wrote:
| What
| iamtheworstdev wrote:
| someone's moltbot is lost
| jhallenworld wrote:
| >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..
___________________________________________________________________
(page generated 2026-02-18 23:00 UTC)