What 50,000 watts of RF energy sounds like through a jumper cable | Hacker News Reader

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

facebook.com

313 points2bluesc153 comments

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

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

What makes it worse than just a burn or a burn due to an electrical shock?

I can't find the reference but a ham operator once told me they can be imperceptible while they're happening.

Normal burns are usually localized to the surface of your skin. RF burns conduct all the way through your tissue, heating from the inside. It's a much deeper, more painful burn that takes an abnormally long time to heal.

(Or so I'm told. So far I've been able to avoid experiencing one myself.)

Unfortunately I wasn't able to avoid the experience, I hit the screw on a silver trimmer in an end stage while looking at another one. Nasty little burn with dead tissue in the center and living tissue all around it. 35 years later it is still there, I don't expect that it will ever properly heal, it's a dead bit in the middle of a living finger.

Yep, I have a RF burns on 2 of my finger tips that I sustained between 5 and 10 years ago... They are dead little bits of flesh. Discolored a deep yellow, there is no feeling left and they feel, I guess I'd describe it as, quasi-numb when touched.

I was an embedded engineer at an RF company and it sort of comes with the territory. We had technicians who had lasted 4+ decades in RF (same company, actually) with scars to show for it. Same story, mostly on their fingers from accidentally hitting hot spots.

What was the power level? We do a lot of RF stuff here and it would be good to know that we're safe.

I got mine at about 100W from a Tronser trimmer.

It really depends on a lot of different factors. Single-digit Watt levels can burn you under the right conditions, though obviously it wouldn't be as severe as at higher power levels.

I was burned by ~300W in the specific cases I mentioned. I think it probably classifies as second-degree burns and (because I was young and dumb) I never did anything to help prevent scarring or heal the tissue besides basic first-aid. Safety first, everything else is secondary.

You mean they conduct from the entry-point to ground, similar to a lightning strike or electrical burn? Or is this more like a radiation burn?

Actually, now that I think about it, it'd actually be most similar to how a microwave heats meat, wouldn't it? Microwaves being within the RF part of the EM spectrum and all. (Though not quite the same, given the lack of dipole interaction with water molecules outside of the particular part of the spectrum microwaves sit on.)

That reminds me of an urban legend regarding microwaves, which doesn't seem entirely infeasible. It involves a man working at a small fast food stand, who worked next to his microwave. Now his microwave was used often, and it had a small hole in the metal screen allowing microwave radiation to leak out. The man slowly starts to feel abdominal pains after a while, goes to his doctor, who diagnoses it as liver problems and recommends drinking less. A couple of months later, the man has died, and the autopsy reveals that parts of his liver were cooked.

I was told this story by my grandmother to prevent me from watching food cook in the microwave. That and cataracts, which can also be caused by heating up things that shouldn't be heated.

There is also the story of Anatoli Bugorski. He was debugging the worlds most powerful particle accelerator when he managed to look into the beam: http://www.strangerdimensions.com/2014/01/13/anatoli-bugorsk...

And he’s become part of popular culture due to the annual satirical year in review panel at the C3 congress giving out the fictional "Anatoli Bugorski Award for applied nuclear safety".

That doesn't sound very feasible. Microwaves work by standing waves, the magnetron doesn't just cook things when outside the oven.

I thought they worked by dielectric heating? Making polar molecules get all frantic and stuff. There is a safety mechanism to shut off the magnetron when the door is opened, and a screen to make the viewing window opaque to microwave radiation, but those can malfunction.

[0][https://en.wikipedia.org/wiki/Microwave#Effects_on_health] [1][https://en.wikipedia.org/wiki/Microwave_burn]

As far as I know, that's the mechanism by which microwave radiation heats molecules, but the specific design of the oven is to produce standing waves so microwaves can become concentrated. I may be wrong, though.

Not wrong -- the safety screen is part of the cavity resonator. But if there's a hole in it, or if you defeat the door interlock, you can still cook yourself with microwaves. In general I'm not too concerned that I'm going to cook my eyeballs by looking at my spaghetti to make sure that it's not exploding all over the inside of the microwave.

Going back to the "discovery" of microwaves for cooking food, the story I heard was a radar tech noticed a chocolate bar melted in his shirt pocket.

Here is a video explaining: https://www.youtube.com/watch?v=7FhwTelc5Tg

The turntable in my microwave failed when I heated up a frozen pizza, and the result was part of it was burned, and part of it was still frozen.

https://en.wikipedia.org/wiki/Microwave_burn#Injury_cases

Disclaimer: I am not a doctor or burn expert of any sort. I am an extra class ham. An RF burn will penetrate more deeply than a "conventional" burn of similar degree, possibly burning nerve cells, circulatory and other structures that an external burn would not. RF burns typically heal very slowly.

I can't compare RF burns to burns caused by electrical current, except to say that electrical current will follow some path of least resistance while RF energy will heat flesh in a pattern corresponding to the field of the radiator and the impedance of the whatever matter absorbs it, so these types of burns will have different patterns.

Also, RF energy is more damaging to tissues that lack blood flow to control heat. Like eyeballs, and testicles.

Right, but for that to happen you'd have to stick your... uh... various balls directly into the path of the RF field. Like at the business end of a big RF horn antenna.

The skin effect should result in a high-frequency AC current propagating at lower tissue depths than a lower-frequency AC current. Why would RF AC propagating in flesh not follow this general rule?

We're getting beyond my depth here, but a few things occur to me. First, I know microwaves `work'; the optimal frequency at which water exhibits the skin effect is about 10GHz, so at 2.45GHz the energy from a microwave oven penetrates meat effectively instead of only frying the surface, as one would expect if the skin effect dominated. Also, I suspect the skin effect could actually cause internal burns; an internal organ that exhibits a strong skin effect at some frequency will cause localized heating on its surface, burning tissue internally.

It's basically like putting your hand inside a microwave oven

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

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

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...

Most tall towers are aggressively grounded. You would need a tower insulated from the ground. A tower used as an element for a low frequency antenna for instance. I strongly suspect that those large black interlocking rings are used as a spark gap for lightning protection in the absence of a solid ground.

Once you were on the tower you wouldn't notice anything. You would have to get between the ungrounded tower and ground.

The interlocking rings are an Austin Transformer [1]. It's the only way to feed electricity to the aircraft warning beacons on the tower without frying the power supply for the light bulbs.

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

There are a few "art installations" where people put fluorescent tubes under power lines.

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

http://www.richardbox.com/press.htm

If I lived close enough I'd be trying to work out some kind of trickle charger for phones.

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

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.

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

You probably could, though I suspect you might need to re-tune between notes.

If you have an old CRT, you might be able to achieve a similar effect with Tempest for Eliza[1].

[1] http://www.erikyyy.de/tempest/

Indeed. One of the more interesting projects I've seen uses a tesla coil discharge as a guitar amp: https://www.youtube.com/watch?v=glrPioGqu3s

A search for "singing Tesla coil" will turn up many more.

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?

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

This video I very interesting. You should submit it.

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.

My guess is that the arc through air gap is functioning as both the detector and speaker here. I suspect that the arc can only be sustained in one direction, probably from ground to the cable, which would give us the required clipping. At the same time, I assume the arc is acting as a plasma speaker, and, as you say, the air and our ear provides the low-pass filtering.

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"

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.

I think "40 W of light" is a great example of why this imprecise, or quite frankly, incorrect usage is troublesome. 40 W of old timey lightbulb light is useful if you want to sit close and read a book in the evening, whereas 40 W of a modern LED bulb light is a great thing to have if you want to fend of a pack of marauding undead.

It's not actually as imprecise as it sounds. A 40W light bulb might produce 1W of light and 39W of heat. Watt is the normal unit of measure for radiant flux, and the lumen is nothing more than "luminous flux" which is radiant flux weighted according to its spectrum.

"40 W of light" in physics terms is quite unambiguous, it means 40 W in radiant flux.

I'm aware that it makes sense to talk about light flux in terms of Watts, I was more getting at it not being obvious what the person using that terminology actually means.

Which is certainly not what the average person on the street means when they use that term.

This may be slightly off topic, but look at this cool LED[0]! It's a 150W 18000lumen LED, which is the raddest thing ever.

[0][http://www.cree.com/LED-Components-and-Modules/Products/XLam...]

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

And you still got it wrong.

This reminds me of https://www.youtube.com/watch?v=Gg_yzRWy9HM

What's wrong with it?

Maybe he thinks it should be 'kiloWatts'. CamelCase impairment?

I can't see the problem either.

I don't think it's a capitalisation problem; when using 'Watt' as a name, e.g. James Watt, you need to capitalise. But the unit is 'watt', with a lower-case 'w'. The symbol is an uppercase W. Reference: Table 3, in "NIST Special Publication 330: The international System of Units (SI)", Taylor et al (2008).

Nor do I think there's a problem with confusing energy and power, as there currently is in the original title.

So, what's the problem? Jaquesm's "And you still got it wrong" comment is unhelpful because it doesn't identify a specific problem. Maybe he feels that the sound doesn't actually come from the cable. Or maybe the cable isn't carrying 50 kW. I don't know. Maybe there is an obvious problem I'm missing.

I believe it's actually the arc producing the sound, otherwise the cable would make the noise regardless of the presence of the arc.

Whether that's what jacquesm is referring to or not, idk.

Yes. The arc is what causes the AM modulation to be translated to moving air at the same frequency as the modulation because the intensity of the arc changes rapidly.

Since this is AM you end up with intelligable sound (for an FM station this trick wouldn't work).

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.

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.

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)?

The bird would be fine, due to the way parallel circuits work (Very little power travels through the more resistant one of two parallel circuits.)

The bird would be dead. RF power will happily fry tissue if you get close enough to the radiator.

Why isn't there a bird / bug / etc cemetary at the base of the tower?

there is. it's very, very noticeable on micro wave towers. the drum like cover on microwave antennas is just a lame regulation to try to save birds. they still die just by passing by. the building were i lived had one that required constant "maintenance" (dead bird cleaning)

I have never seen this, and I work with microwave towers nearly every day.

The 'drum like cover' is called a radome, and it's primary purpose is to reduce the wind loading of the microwave dish. It also serves to protect the usually sensitive feedhorn inside the dish, keep out bird nests, ice, water, etc...

The common cause of bird deaths around radio towers is collision, not RF energy. In Florida it is very common to see osprey nests build on/in/around towers. Microwave dishes are a common location because they provide a large horizontal surface to support the nest. See Wikipedia article 'Towerkill'

https://en.wikipedia.org/wiki/Towerkill

uh. have a completely different experience. mostly with south america and 15+ years ago. i recall very well the impression of the row of dead birds in the roofs. granted, i only got near the towers 4 times in my life.

Excuse my ignorance, but wouldn't the bird need to be grounded for the power to jump? Or does that only apply to electrical circuits?

the microwaves being transmitted themselves can be enough to kill

This is in fact a profound question.

The physics of electricity propagation in a powerline circuit is fundamentally the same as the propagation of FM radio waves, or even the beam from a flashlight. All of these examples involve electromagnetic energy propagating at the speed of light. So why do we need wires for powerlines, but not for propagating radio signals or light beams?

The principle is that light (in a vacuum at least) travels at a constant but non-infinite velocity, c. Hence, the electrical wiggle received at an observer's location now i.e; (x,t), has been caused by some earlier wiggle conducted by the source (x',t') such that the t-t'=(x-x')/c. We should expect that the effect of this 'time delay' is more profound if the source is wiggling faster in time.

A more specific way to state this is that the electromagnetic power radiated into free space by a dipole increases as the square of the dipole moment and the fourth power of the frequency. Now compare a powerline (60 cycles/sec), with FM radio (100 Million cycles/sec), and with the light from a flashlight (500 Trillion cycles/sec). That's why even atomic dipoles can produce intense visible light, while it would take a very very large dipole to radiate a similar intensity at 60 cycles.

Feynman Lectures Vol.II is absolutely the best reference to learn this stuff.

That is not to say that a bird needs to make contact with two wires on a utility line, in order to suffer harm. If the line voltage is high enough (e.g; 110,000 Volts, as in high-tension power transmission), an electrical corona would form around the line from electrostatic effects. The corona is actually ionized air indicating the high electrostatic field strengths in the region, it can emit a bluish glow and growl at 60 cycles. Birds can no doubt sense this corona & stay away.

> Birds can no doubt sense this corona

So can humans, it's a crackling sound.

Yes and no.

How do you think the human standing right next to the tower is not getting fried?

Humans climb live radio towers routinely.

The tissue absorption of RF energy at common AM station frequencies(below 2mhz) is negligible. Maximum absorption happens around the frequencies commonly used by FM stations (about 100mhz)

I have climbed near an live FM antenna. You can feel the heat(well, radiation, converted to heat by your body tissue) from the antenna, it feels like a heat lamp. Your eyes are the most sensitive parts as they have the least ability to dissipate excess heat. The old rule-of-thumb is, if your eyes are watering, you're too close to the antenna. But like most things 'the way they use to do it' -- by that point damage is already being done. Cataracts are one of the first signs of RF induced tissue damage.

It would take many thousands watts, transmitted at frequencies well above common AM frequencies to cause any sort of instant damage. I have never seen a field of dead birds near even major FM stations broadcasting with 50kw+ power.

I've accidentally fried small birds at ~1KW around 100MHz. It all depends on where they sit and how the power is radiated. Near the end on a Yagi is not a good spot.

Why are you pointing your yagi at small birds? :-)

I know, it's sad.

I made a point of swishing the rotor side-to-side a couple of degrees after I figured out where the dead sparrows came from. That caused them to fly off and once the transmitter was on they'd stay away from the antenna.

I am also curious about the cable. At the start of the video, its upper end is clamped on to a part of the antenna. The guy appears to be about take the lower end off what I am guessing is a grounded part, then he decides to give the demonstration. So, in the beginning, is this a live antenna that was shorted to ground while still being powered? (perhaps because it was being worked on?) If so, it seems a rough way to handle the transmitter, though I suppose it must be robust enough to handle lightning strikes (you can see two rods with balls on the end that I guess make a spark gap.)

Alternatively, could this be an unpowered antenna that is picking up signal from a nearby powered one?

Alternatively, could this be an unpowered antenna that is picking up signal from a nearby powered one?

I'm pretty sure this is what's happening. From past experience with high voltage arcs (admittedly at 60hz, not ~1 MHz), I don't think we're seeing more than a few hundred watts of power in that arc. Also, if this tower was actually the one transmitting that signal (presumably 50kW is the transmitter power) they'd shut it off or switch to a different antenna for maintenance on this one. If you shorted the output of the transmitter at the point where it's normally driving a resonant load, the best possible case is that it would trigger some kind of automatic shutdown on the final amplifier.

gelo's reply (https://news.ycombinator.com/item?id=11081227) suggests that the 'nearby powered antenna' is actually supported by the mast, and the mast itself is not an antenna.

Why were they shorting the tower?

Since the tower is metal, it will inherently start to resonate to the transmissive power. (The same effect can be seen when you touch a phono connector to an active amplifier, the 50/60Hz hum can be heard because you are absorbing some of the mains voltage energy radiated around you.)

When you transmit, any metallic object around the antenna can affect the impedance of the system. Usually the system is tuned with respect to the antenna and mast structure. At 50kW the antenna mast structure is resonated so hard by the antenna that high RF induction is present in the mast structure itself. Mast maintenance is normally done with the transmitter turned down or off entirely. Since this is a broadcast mast, this is not so easy. Grounding the mast structure may imbalance the tuning slightly but not enough to be of a concern with damaging the PA's. But the safety of maintenance engineers is a mandatory requirement.

Why not ground the mast anyway?

If you are inductively resonating a gigantic mast, you are also assisting in improving the gain of the irradiated signal. Hence why in the video the bottom of the mast has a black block of plastic/rubber.

With most AM stations, the tower itself is the radiator. That's the reason for the insulation from ground. If the tower were grounded, it would not be able to transmit a signal at all. In the video, while that cable is attached, the tower cannot transmit.

I wasn't sure about the device they were shorting so I asked the chief engineer for several large radio stations in the area.

That device is a lighting transformer [1][2] -- it allows AC power to be coupled to the tower, to power the lights, without a direct connection, which would severely impact the tower's ability to radiate RF energy. The two little balls is called a lightning gap, it gives lightning a path to ground, other than the connection to the transmitter, since the tower itself is not grounded.

[1] http://www.austin-insulators.com/radio/xfmr.html

[2] http://www.sonifex.com.au/?media_dl=3300 (PDF)

i can understand the need for the large towers to TX AM band signals but grounding a directly fed antenna like that would kill the PA. You'd really screw up the SWR.

I believe there is some sort of protection circuit that keeps such an event from destroying the PA.

> With most AM stations, the tower itself is the radiator.

Right. At those low frequencies, yeah, you need a pretty huge chunk of metal to radiate efficiently.

So you're telling me that giant ass arc was caused by induction??? Holy crap!

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

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?

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...

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

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.

Oh boy. WWV is great when testing out ham radio propagation for the same reasons it was a nightmare for you. Powerful signal being broadcast between about every major amateur band. 2.5, 5, 10, 15 and 20 MHz.

BEEEP dooo dooo dooo dooo

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.

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

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.

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?

Wow, can anyone explain this?

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

If you listen to an FM signal interpreted as AM you can often still make out the audio, it'll just be very clipped and noisy. That was the result when I did this with an RTLSDR, at least

Same way as a plasma speaker

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

Or, on a larger scale, a Zeusaphone/Thoremin: https://www.youtube.com/watch?v=3ff_AXVlo9U

https://www.youtube.com/watch?v=hgll-XTqcS4 (youtube-dl with mpv fullscreen recommended)

Dumb question is it also creating the piano like sound in that video with the electricity? Very cool to watch.

Yes! That's all done with the plasma channel expanding and (therefore) contracting at audible frequencies.

(edit: I'm way wrong on the piano. arjie's correct about the backing track)

There's a backing track.

It would be cool to see a guitar amplifier that worked like this. It seems dangerous, but that would be awesome to hear/watch.

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.

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.

Reminds me of a Gilligan's Island episode, Hi Fi Gilligan: https://www.youtube.com/watch?v=3x1XHv0sxro

Lucille Ball talking about picking up radio signals in her fillings. https://vimeo.com/72473069

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 to increase the limit from 500kW to 750kW(!).

It's a big deal in the ham community, but I only learnt latter that while US stations were limited to 50kW - other parts of the world didn't have such restrictions. Parts of the Middle East have 2,000kW stations. [2]

You can get a full download on the Crosley WLW station in this video: https://www.youtube.com/watch?v=CbHjcwIoTiY

[1] http://www.ominous-valve.com/wlw.html

[2] https://en.wikipedia.org/wiki/Transmitter_Solt

Actually, Solt is not Middle East, but in Central Europe. (I live ~50 km from it.) But yes, it's 2 MW, and at night, it can be heard using conventional receivers as far as Belgium.

Corrected link: http://www.engineeringradio.us/blog/2012/12/the-continental-...

Well, the Warsaw Radio Tower used to be the tallest man-made structure in the world until it collapsed due to a guy rope failure - and it had a 2 megawatt transmitter, it could be received literally anywhere in the world:

https://en.wikipedia.org/wiki/Warsaw_radio_mast

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.

It's definitely not an urban legend - I witnessed this first hand at a high school friend's house, where headphones attached through long extension cables across the room would pick up the nearby AM transmitter.

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 the cone). From what I understand from my undergraduate analog signals course I'm suspicious of the signal actually coming from the transmission tower itself, unless the speakers had just the right configuration to act as a simple diode-rectifier envelope receiver (terminology likely to be incorrect), which I would think of as unlikely for an FM signal.

It may be that the signal came from some other path related to the relaying of the signal from the studio (~1 mi away) to the tower, but I don't know enough about the specifics of the radio station's configuration to say more.

That happened to me sometimes, living in the UK --- my computer speakers would come on in the middle of the night and start whispering to me in French. It was exactly as creepy as it sounds.

I think I did eventually pin down which station they were picking up, but I've forgotten now. Interestingly, since I've moved to Switzerland, it's stopped. Maybe the signals don't get through Swiss customs.

A diode isn't actually required for AM reception, it just happens to be one of the better ways if doing it. In fact, any non-linearity in a circuit will act to demodulate AM signals, as the video and your friends experience nicely demonstrate.

He was talking about FM, not AM. Which makes it rather weird, as you actually need more of a circuit to decode it.

In college I lived in an apartment near a highway and my keyboard amplifier would pick up CB radio from truckers. I had to physically unplug it at night time.

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...

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

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

I think it depends on what country you're in. In some countries, they have to block pages if you're not signed in for legal reasons (since they can't legally track you).

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.

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

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

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

Here's a copy...

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

which I will remove at some point

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

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.

i mis-read your comment - it has no affect at all as its not whats transmitting 50kW!

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, ...

eh i wasnt expecting to be right. Although i would say they usually use heavy duty coax at 50ohm - i believe - not sure though

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

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.

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.

Behind login wall.

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

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

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.

nitpick - watts is a measure of speed - joules per second

I'd call it a rate, not a speed. Speed is specifically distance per unit time, not energy per unit time.

Good point but even then we tend to use power when talking about energy per unit time.

Joules = energy (how much work you can do)

Watts = power (how fast you do the work)

50kw for 1 nano second is not going to have much of an effect

Reply on news.ycombinator.com