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What 50,000 watts of RF energy sounds like through a jumper cable

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Re: What 50,000 watts of RF energy sounds like through a jumper cable

#111

Post by hippich »

batat wrote: post #84
tlrobinson wrote: post #9

Even better: some crazy Russian/Ukrainian kids listening to the local radio station through weeds (and occasionally getting some minor RF burns): https://www.youtube.com/watch?v=82s5Q3GIO9I

It's abandoned radio station in Brovary, Ukraine, I've been there several times. There were two antennas — 180 m and 270 m with 100 and 150 kwt transmitters (later up to 250 kwt). Until 1988 they were used for radio jamming (BBC, Voice of America, Deutsche Welle), later for radio broadcasting [1] AFAIK you could get serious burns [2][3] even when antenna was not powered any more. In this case it works just like huge…

Regarding "AFAIK you could get serious burns [2][3] even when antenna was not powered any more", does it mean I can get "free" electricity from "thin air"? Did someone try this already?

Re: What 50,000 watts of RF energy sounds like through a jumper cable

#112

Post by sathackr »

philh wrote: post #78

Does a tower like this only broadcast one radio station? That's not what I would have naively expected. But if not, why do they pick up that specific one?

I've never heard of it, but as the other reply mentions, it's possible.

If you are near an AM station, you can make a radio with just a earphone(now called ear bud?), a diode, and a piece of wire.

You will pick up all nearby stations, but one will likely be stronger/closer than the rest, so you would hear that one.

A slight improvement of that is the 'crystal radio' that adds the ability to tune to a certain station. [1]

It is common for people living near AM stations to hear the radio signal induced into their house/business wiring. It's a common problem with landline telephones near these stations, you can hear the radio in the phone while you're trying to use it. Intercom systems are also vulnerable.

You've probably also heard this from time to time when someone with an illegal CB amplifier uses their radio near a business with an intercom system. It will typically briefly bleed into the intercom system, with everyone looking around trying to figure out where that noise came from. This may be common only in the south, I'm not sure how prolific CB radios are throughout the country.

[1] https://en.wikipedia.org/wiki/Crystal_radio

Re: What 50,000 watts of RF energy sounds like through a jumper cable

#113

Post by kabdib »

philh wrote: post #78

Does a tower like this only broadcast one radio station? That's not what I would have naively expected. But if not, why do they pick up that specific one?

I used to live in Fort Collins, Colorado, a couple of miles from the antenna for WWV, the broadcast time standard from the National Bureau of Standards (that'll date me, it's called NIST now).

Electronics was one of my hobbies. Most of the noise in my circuits was that damned time signal. I could pick it up with just about any length of wire and anything that would act as a diode. A transistor. A pin on a chip -- I had a DRAM coughing up "At the tone, the time will be..." once.

At least I usually knew what time it was.

Re: What 50,000 watts of RF energy sounds like through a jumper cable

#114

Post by upofadown »

hippich wrote: post #111
batat wrote: post #84

Earlier quoted context omitted.

It's abandoned radio station in Brovary, Ukraine, I've been there several times. There were two antennas — 180 m and 270 m with 100 and 150 kwt transmitters (later up to 250 kwt). Until 1988 they were used for radio jamming (BBC, Voice of America, Deutsche Welle), later for radio broadcasting [1] AFAIK you could get serious burns [2][3] even when antenna was not powered any more. In this case it works just like huge…

Regarding "AFAIK you could get serious burns [2][3] even when antenna was not powered any more", does it mean I can get "free" electricity from "thin air"? Did someone try this already?

You sure can. The normal fair weather voltage gradient in the atmosphere is around 100V per metre. When there are close thunderstorms this increases. Unfortunately for energy collection air is quite insulative. That's also fortunate in that we don't get shocks all the time just from standing around in an environment where your head is 200V different than your feet.

Popular Science once ran an article that showed how to build an electrostatic motor that ran off the atmospheric electricity you could get with something like a wire used as a kite string.

* https://en.wikipedia.org/wiki/Atmospheric_electricity

Re: What 50,000 watts of RF energy sounds like through a jumper cable

#115

Post by bschwindHN »

michael_h wrote: post #109
paulgerhardt wrote: post #39

Earlier quoted context omitted.

That was one specific station - the infamous WLW / W8XO - the first and only US station authorized to operate at 500kW of power.[1] To give you an idea of how powerful that is, take a look at their coverage map: http://i.imgur.com/Aigz1Zh.jpg The back story is kind of interesting. It was run by Powel Crosley - a sort of 1930's version of Elon Musk. Advertising revenues from the station were so successful he applied t…

I grew up about 5 miles from that antenna. I can't say I ever heard the radio through the wiring in my house. The Voice of America antenna array down the street though? I could hear it clearly through my stereo speakers when everything was turned off. It's been dismantled, but I can imagine the number of ghost stories that it spawned. Just sitting in your house, and then you faintly hear a man speaking German...

It's weird seeing people on reddit who grew up in the same town as you, but it's even weirder seeing it on Hacker News for some reason.

I never heard the broadcasts through metal objects in the house either, but maybe they scaled back the power in the time I grew up there. Never heard any VoA broadcasts either.

Re: What 50,000 watts of RF energy sounds like through a jumper cable

#116

Post by Piskvorrr »

dest wrote: post #104
Piskvorrr wrote: post #71

Earlier quoted context omitted.

Your first explanation is far more likely: water conducts sound waves far better than air.

IIRC, sound waves are hugely dispersed in water (group/phase velocity change with frequency) so it would be difficult to understand what the speakers say / to enjoy the music, etc...

Yup. Quality is worse, but the sound carries much longer distances.

Re: What 50,000 watts of RF energy sounds like through a jumper cable

#117

Post by gelo »

JohnDoe365 wrote: post #95
gelo wrote: post #82

50000W of RF power is approximately 355kV - if you work out based on that 1W dBm is 7.1 Volts.

The pictured parabola antenna likely has a gain around +20dB. Would that change your calculation?

i don't think it would change (probably wrong) since the active energy is only generated by the final PA's in the system. the Antenna's gain is only from the passively reactive design. Its like making a violin string resonate by only moving the bow and not physically the string.

Re: What 50,000 watts of RF energy sounds like through a jumper cable

#118

Post by xhrpost »

connorlee wrote: post #7

Amplitude Modulation, or AM, works by modulating the sound on the "peaks and valleys" of the frequency. If you were to look at the waveform of the carrier frequency, you would see it as variance in the "power levels" of the signal, going higher and lower depending on what's being sent. Because of how AM works, you can actually hear what's being transmitted by causing an electrical arc. It's the same concept of hearin…

Came here to ask this very question. Thank you. I take it then that a signal using frequency modulation or phase modulation (is that done anywhere?) wouldn't work then? Also, probably the same reason a ground loop in a home entertainment system will pick-up local AM stations. Edit: also, why does this work with the given RF frequencies which for AM are still much higher than audible sound frequencies?

Re: What 50,000 watts of RF energy sounds like through a jumper cable

#119

Post by acveilleux »

plorg wrote: post #49
URSpider94 wrote: post #12

Earlier quoted context omitted.

The voltage applied to the cable is directly proportional to the audio signal, overlaid on a ~1 MHz carrier. All you need is a mechanism that transforms those voltages into vibrations or pressure waves. Presumably, since it seems to happen only when he's striking an arc, it's related to the local heating of the air in the gap ... But I guess it could be electromagnetically induced vibrations of the cable or the tower…

I have a friend who lives as close as one can legally live to a 100kW FM transmitter. He received a pair of very cheap speakers when he built a new computer but was unable to use them because if they were plugged in the radio signal would come right out of the speakers. It seemed that the signal path into the speakers was through the input wire (rather than, say, the power cable or the wires between the amplifier and…

I had a pair of really cheap computer speakers once that would catch faint FM signal whenever they were powered. I was in a 6th story loft at the top of a hill with a clear view for maybe 30km from my window but not actually close to any transmitter. I blame the 5$ speakers, not the FM transmitter.

That said, I didn't live 300m from 100kw...

Re: What 50,000 watts of RF energy sounds like through a jumper cable

#120

Post by jonahx »

upofadown wrote: post #114
hippich wrote: post #111

Earlier quoted context omitted.

Regarding "AFAIK you could get serious burns [2][3] even when antenna was not powered any more", does it mean I can get "free" electricity from "thin air"? Did someone try this already?

You sure can. The normal fair weather voltage gradient in the atmosphere is around 100V per metre. When there are close thunderstorms this increases. Unfortunately for energy collection air is quite insulative. That's also fortunate in that we don't get shocks all the time just from standing around in an environment where your head is 200V different than your feet. Popular Science once ran an article that showed how…

What's required for a tower to become electrified from the air? I feel like I've played on other metal towers in my life that were inert...
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