Tunnel Radio: How Signals Reach Drivers Underground? RW rip...

[ThaDood]

https://www.radioworld.com/columns-and-views/tunnel-radio-how-signals-reach-drivers-underground    We don't hear much about Leaky-Cable Broadcasting. Heck, who still makes cables that could even do that, Belden? Still, a permissible way to broadcast license-free. (Thank you Boomer!) Oh BTW, this also works in mines.

[tybee]

That's a good article, I hadn't seen it yet. Glad you posted it. done a lot of research on that myself. I'm pretty sure I've  got newspaper clippings of everyone of those installations he talked about.
Incendently, that first one way back in1939 at George Washingston Bridge, the equipment went into storage after the closing of the 1940 New York Worlds Fair,.. And it was that exact same equipment Halstead used on the bridge that was transferred to the Lincoln Tunnel 11 years later - with exception to the original wire recorder/player that had fed the audio .. by that time technology had improved.

I had always found it peculiar that the FCC found it neccessary to specify that "oil storage tanks are not tunnels" as found in FCC OET BULLETIN NO. 63 (October 1993)
http://transition.fcc.gov/Bureaus/Engineering_Technology/Documents/bulletins/oet63/oet63rev.pdf
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Tunnel radio systems
Many tunnels have naturally surrounding earth and/or water that attenuates radio waves. Transmitters that are operated inside these tunnels are not subject to any radiation limits inside the tunnel. Instead, the signals they produce must meet the Part 15 general radiated emmission limits on the outside of the tunnel, including it's openings. They also must comply with the conducted emission limits on the electric power lines outside of the tunnel.
Buildings and other structures that are not surrounded by earth or water (e.g oil storage tanks) are not tunnels. Transmitters that are operated inside such structures are subject to the same standards as transmitters operated in a open area.
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There's another interesting thing found in their chart on page 5 (which I just noticed): Authorization Procedures for Part 15 Transmitters, showing that part 15 transmitters used for tunnel radio, campus stations, other AM carrier-current, perimeter protection systems, and systems at or below 490 kHz , all require "Verification"[/b]
Leaky coaxial cable systems also require only "Verification", however, that only "for operation exclusively in the AM broadcast band". If used in any other frequency then it needs "Certification"

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"All other Part 15 transmitters" require "Certification"[/b[
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We all know about Certification and Compliance of part 15 transmitters, but I cant say I've ever heard of Verified Part 15 transmitters befote.