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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

#141

Post by cocoablazing »

topspin wrote: post #45
therein wrote: post #14

Earlier quoted context omitted.

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

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 p…

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?

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

#142

Post by DanBC »

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?

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.

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

#143

Post by HeyLaughingBoy »

scruple wrote: post #56
jacquesm wrote: post #36

Earlier quoted context omitted.

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…

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

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

#144

Post by lfowles »

StavrosK wrote: post #101
50CNT wrote: post #98

Earlier quoted context omitted.

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.

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.

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

#145

Post by mmagin »

mannykannot wrote: post #99
exabrial wrote: post #13

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)?

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…

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.

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

#146

Post by jackhack »

Already__Taken wrote: post #44
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…

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

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.

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

#148

Post by fryguy »

50CNT wrote: post #98
StavrosK wrote: post #92

Earlier quoted context omitted.

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 ]

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.

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

#149

Post by SixSigma »

ridgeguy wrote: post #147
SixSigma wrote: post #25

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

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

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

#150

Post by gelo »

cnvogel wrote: post #130
gelo wrote: post #82

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

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…

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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