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

[tlrobinson]

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

[batat]

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 receiving antenna, getting kilowatts of RF energy directly from atmosphere. Before the thunderstorm ropes holding the antenna literally glowed due to corona discharge effect.

A few years ago both antennas were demolished [4][5]

[1] http://vk.cc/4LQeGa (wiki, Ukrainian)

[2] http://io.ua/20405915p

[3] http://io.ua/20405932p

[4] https://www.youtube.com/watch?v=j6NgzzFrCv4

[5] https://www.youtube.com/watch?v=Pn6sLpDS0Ks

[voltagex_]

I don't think I'd want even minor RF burns - nasty nasty stuff.

[StavrosK]

Wait, is that thing just lightly fenced and casually has this much current flowing through it? Isn't that basically a death trap?

[connorlee]

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 hearing a "buzz" from high voltage power lines, except in a controlled fashion to produce sound.

[LesZedCB]

ElectroBOOM has a cool video[1] on youtube talking about some of that! His videos are some of my favorite.

[1] https://www.youtube.com/watch?v=L5E4NiP4hpM

[JoeAltmaier]

The carrier frequency is way above the hearing range. So it has to be shifted to the audible range. That happens by clipping and filtering. The arcing must be doing that somehow. Probably clipping; the low-pass filtering is done by the air/your ear.

[xhrpost]

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?

[Already__Taken]

So could you tune into the singing tesla coils with an AM radio is that the same idea?

[estomagordo]

19 comments and not even one mentions that Watt, with a capital W, measures power, and not energy? I'm assuming 90% of posters know this, but it still bugs me.

A modest proposal: "What 50 kilowatts of RF power sounds like through a jumper cable"

[Nutmog]

I think that usage is OK. It's like saying "40W of light". In this case, it tells us there's some RF energy and also that it's RF energy of the "50 kW" type.

[jacquesm]

> What 50 kilowatts of RF power sounds like through a jumper cable

And you still got it wrong.

[luxpir]

A link to the CDN-served file directly, if anyone wants it:

https://video.xx.fbcdn.net/hvideo-xlt1/v/t42.1790-2/12709279...

Not the prettiest thing, but there you have it.

[i336_]

This is now returning "URL signature expired".

The guaranteed way to do this is just to grab and use youtube-dl. It supports almost everything nowadays, and it's where all the updates and maintenance goes. Passing the OP URL got me a copy of the video perfectly.

[exabrial]

So dumb questions:

Why were they shorting out the tower? (What was the purpose of the cable)

What are those rubber things?

What would happen to a bird that landed on the tower (not grounded)

What about a large metal helicopter (if it didn't crash)?

[skrpwr]

This works with plants too. https://www.youtube.com/watch?v=6Scm-tKTHls

[philh]

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?

[sathackr]

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

[kabdib]

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.

[beedogs]

AM towers can broadcast more than one frequency at a time, but I'm not sure how common it is in practice.

http://www.radioworld.com/article/four-am-stations-sharing-o...

[nielsole]

I was once in a completely empty swimming pool (~25*10 m size) The surface of the pool was completely undisturbed. When I put my head under water I could hear a radio voice. Since I could not rule out the possibility that it was simply audio from nearby speakers that I simply could not hear through the air, I was always wondering whether it would be possible to listen to radio waves in water.

[tombrossman]

Underwater speakers exist (think synchronized swimming or a PA system at a public pool). The sound quality isn't super but voice quality is good. Is it possible the pool was equipped with one?

[Piskvorrr]

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

[andromeduck]

You probably can't because, if nothing else, the water should act like a faraday cage.

[ronreiter]

Wow, can anyone explain this?

[URSpider94]

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 structure ...

There used to be stories, not entirely urban legend, of people who lived close to AM towers hearing the station in the wiring of their home, or in their dental appliances. Not impossible, considering that many AM stations broadcast with 50kW of power (like the one in this video) and can be received across a large swath of the country.

[AndrewKemendo]

Same way as a plasma speaker

https://www.youtube.com/watch?v=PJpn2PzhvP4

[xwintermutex]

I guess it is because of the use of amplitude modulation [1], where the envelope ("strength") of the carrier (that is some higher frequency signal) follows the signal that is modulated onto it (speech, in this video). With say FM it wouldn't work, I presume.

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

[madez]

I can’t watch this video without an account. A click on the video leads me to the login page. Is there a mirror?

[hudibras]

I don't have an account and it played fine. No explanation of why tho.

[redblacktree]

Another poster shared a direct link to the CDN, may help: https://video.xx.fbcdn.net/hvideo-xlt1/v/t42.1790-2/12709279...

[igravious]

I don't have an account and it played just fine. Don't know why though because normally I get a login page like yourself.

[exodust]

Here's a copy...

http://ozimg.s3.amazonaws.com/video/RF_energy_through_jumper...

which I will remove at some point

[doguozkan]

You could try unblocking Facebook domains if you're using Privacy Badger.

[symmetricsaurus]

I got a login screen that popped up after a while. Pressing ESC got rid of it.

[carapace]

It is a plasma speaker? https://en.wikipedia.org/wiki/Plasma_speaker

[gelo]

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

[cnvogel]

No. Power generally is proportional to the voltage squared (P∝U²). P=U²/R → U=√(PR)

The numbers you quote (1W [not dBm!] is 7.1V) make me believe that you assume an impedance of 50Ω.

    In [1]: math.sqrt(1*50)     # P[in W] * R[in Ohm]
    Out[1]: 7.0710678118654755  # U[in V]

So, in an hypothetical cable of 50Ω impedance, 50kW of RF power is...

    In [2]: math.sqrt(50e3*50) # P[in W] * R[in Ohm]
    Out[2]: 1581.1388300841897 # U[in V]

about 1.6kV(RMS).

Note, though, that with large installations it is likely that there are a few individually tuned feeds. And the cable might not be a 50 Ohm cable, but maybe a chicken ladder (two strands separated by fixed spacers), large-area waveguide, ...

[JohnDoe365]

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

[elaus]

In my home town we have a large broadcasting tower for MW/UHF radio and a lot of the elder people tell stories about how they were able to listen to the radio via the plants (e.g. cucumbers) in their garden

[snarfy]

Power transmission lines have a similar effect when they are disconnected. My father was a lineman and told stories of hearing radios, intercoms, etc when working with HV lines.

[w8rbt]

Never touch or even stand close to an antenna that's transmitting. Even small mag loops with 10 watts of power will cause serious burns if touched.

[stefanix]

Behind login wall.

[lucb1e]

Same here, need a Facebook account to play the video. Mirror, anyone?

[dan1234]

I’m not logged in but the video plays fine here.

[trhway]

so, pedantically, it isn't through the jumper cable - the sound is generated by plasma between the cable and the tower. I think i heard something about "plasma speakers" before.