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
~~~~~~~~~~~~~~~~~~~~
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.
~~~~~~~~~~~~~~~~~~~~

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"

~~~~~~~~~~~~~~~~~~~~
"All other Part 15 transmitters" require "Certification"[/b[
~~~~~~~~~~~~~~~~~~~~


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.

[tybee]

Your post had got me thinking about it again and something I've always been puzzled over was the installation cost which had ranged between $150,000 and $200,00 per instalation.. Your talking about a broadcast of a low power AM signal inside an enclosed space -- WHY SO EXPENSIVE??..
Today (or even then) you could remove the crystal out of something like a Rangemaster install it in the middle of the tunnel and you'd have a compliant AM signal that broadcast across the entire band as effectively as those $200,000 leaky cable systems did when they were more common! - no?

But here's something interesting I previously missed.. Evidently there were two companies going by the name "Tunnel Radio of America" - The still existing is interestingly a "Women-Owned Small Business"

So, there was the original one:

● Broadcasting Sep 27 1982 (page 41)
"...Tunnel Radio of America, Hollywood, Fla., whose president, Rodger Skinner, first developed a transmitter which, through a unique filtering and tuning process, can broadcast one signal simultaneously on 24 AM radio frequencies for reception by com- muters traveling through tunnels, is franchisng its technology in major markets around the country and abroad. Skinner developed the transmitter in 1975... The start -up costs on the average range between $150,000 and $200,00.."

And then the existing women-owned one in Oregon:

https://miningdirectory.org/listing/tunnel-radio-of-america.html
● Tunnel Radio of America is an ISO-9001 certified manufacturer and Women-Owned Small Business, headquartered in Corvallis, Oregon. For 35 years, Tunnel Radio has distinguished itself as the trusted designer, manufacturer and installer of specialized radiating-cable antenna systems (“leaky-feeder”) for underground or unreachable areas... ...For more information, visit www.tunnelradio."


Of note, there was also a company called "Tunnel Radio USA" in the 1970s.. I have to look but I think that may have actually been the same guy as Tunnel Radio USA was (Skinner)