Here’s a story from OK about copper thieves targeting a tower. It was over twice the height, but apparently had a negligible amount of copper. Of course, there’s no guarantee these thieves did a lot of research on how much they could expect…
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Contractor: “Believe me, we’ve learned our lesson here. Never again will we build a radio tower out of 18-carat gold”.
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The thing that always gets me is thieves cutting copper from live circuits. Doesn’t matter if it’s AM, FM, or a distribution wire, there’s a LOT of power flowing through those systems. I mean these are serious power arcs that are going to sizzle around whoever is foolish enough to try.
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DH and I worked with a local radio station for a while. They had multiple stations and formats all broadcasting out of a location in a strip mall ‘downtown’, but the towers were scattered all over, miles from the station(s) itself. Usually they were in rural areas away from valuable property and high rises which might block the signal. Until someone reported them being off the air or the tower missing, it’s not surprising it could vanish.
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There’s a lot going on in that video that I don’t understand. I get the main point - much power - but there are strange details. Why does an AM quality radio sound come out when he is letting the arc flare?
About – 10-15 years ago so vandals cut through one of the guy wires on a tower in San Ramon (East SF Bay) - it was apparently entirely deliberate, but they never caught the perp, sadly. Nothing was stolen, just some guy out for shits and giggles.
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Basically anything that an AM signal causes to vibrate will make noise. Metal barns, metal fillings, etc. The power arcing to ground is the same shape as the power being sent into the air, so as the arc heats the air, it causes vibrations that are correlated with the audio signal.
Now, the carrier frequency is way above hearing range, but the properties of air that make it typically carry sounds we can hear must act as enough of a filter to bring it down. I’m not familiar with the physics, but the point is that AM is very ‘natural’ to decode. This trick wouldn’t work with FM.
ETA: decent discussion that’s a little less ELI5 than this
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$100, wow they probably spent that much just on gas.
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The ‘not a lot of listeners’ concept dawned on me yesterday. Plus AM radio; could have been down for days without even the ‘owners’ noticing.
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It’s in the name. Amplitude Modulation (AM) is a high frequency transmission (a “carrier wave”) where the carrier signal’s power is directly proportional to waveform of the audio signal. When the “amplitude” of the audio wave is higher, the transmitter power is higher, and vice versa. That’s the “modulation”.
Once he created the arc, the plasma was pulsing at exactly the power running through it. When the transmitter was sending more power through the arc it created more plasma; less power, less plasma. More plasma heats and expands more air around it. Less plasma, the less the surrounding air expanded. The differences in air pressure were vibrating the air precisely in time with the modulated power, which was the amplitude of the original audio signal, making it perfectly audible.
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Haven’t any of y’all seen The Iron Man?
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Between books, MCU films, anime, and some Japanese horror film from the 80s, you’re going to have to be more specific.
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a rival AM station? in this century?
It would make it trivial to narrow down the suspect list.
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That is actually a lot less than I would have guessed! By an order of magnitude
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Looking at AM groups around the world, I suspect there are some uses in the ongoing war in Ukraine.
You mean it’s time travelers?
Jeff Geerling is well known for his Raspberry Pi videos, his father, Joe is a radio engineer.
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