
What 50,000 watts of RF energy sounds like through a jumper cable - 2bluesc
https://www.facebook.com/W8MSU/videos/vb.210772745607630/1110939655590930
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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](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](http://vk.cc/4LQeGa) (wiki, Ukrainian)

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

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

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

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

~~~
hippich
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?

~~~
upofadown
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](https://en.wikipedia.org/wiki/Atmospheric_electricity)

~~~
jonahx
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...

~~~
upofadown
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.

~~~
jloughry
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](https://en.wikipedia.org/wiki/Austin_transformer)

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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.﻿

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

~~~
pdkl95
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/](http://www.erikyyy.de/tempest/)

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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"

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

And you still got it wrong.

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zurn
What's wrong with it?

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sathackr
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.

~~~
jacquesm
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).

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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...](https://video.xx.fbcdn.net/hvideo-
xlt1/v/t42.1790-2/12709279_1695997427283635_55022438_n.mp4?efg=eyJybHIiOjM2NSwicmxhIjo1MTIsInZlbmNvZGVfdGFnIjoic3ZlX3NkIn0%3D&rl=365&vabr=203&oh=1f3406291ae0de3e377fc3c4d1e3d88e&oe=56BCAA54)

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.

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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)?

~~~
gelo
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.

~~~
sathackr
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](http://www.austin-
insulators.com/radio/xfmr.html)

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

~~~
gelo
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.

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

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

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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?

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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.

~~~
fluxquanta
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

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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.

~~~
Piskvorrr
Your first explanation is far more likely: water conducts _sound_ waves far
better than air.

~~~
dest
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...

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

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ronreiter
Wow, can anyone explain this?

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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.

~~~
plorg
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.

~~~
rcxdude
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.

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

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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.

~~~
phantom784
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).

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carapace
It is a plasma speaker?
[https://en.wikipedia.org/wiki/Plasma_speaker](https://en.wikipedia.org/wiki/Plasma_speaker)

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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, ...

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

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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

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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.

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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.

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stefanix
Behind login wall.

~~~
lucb1e
Same here, need a Facebook account to play the video. Mirror, anyone?

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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.

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

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

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

