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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

#131

Post by jloughry »

upofadown wrote: post #121
jonahx wrote: post #120

Earlier quoted context omitted.

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 g…

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

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

#132

Post by malexw »

JoeAltmaier wrote: post #129
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…

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.

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

#133

Post by exodust »

jrockway wrote: post #21
ronreiter wrote: post #3

Earlier quoted context omitted.

Why is that an issue?

I've noticed that a lot of users have various vendettas against certain companies, and they like to pretend to be outraged whenever they have any opportunity to mention their dislike for the company. In this case, a link to Facebook was provided, so it was the perfect opportunity for a rant about Facebook, right? (In the case of gnu8, it appears they merely hate everything unilaterally which I suppose is refreshing.…

Anti-rant?

I got the "you must login to continue" prompt on Facebook, but managed to save the video and upload as a good old static mp4...

the video is low quality, as is the version on FB.

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

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

#134

Post by exodust »

madez wrote: post #48

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

Here's a copy...

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

which I will remove at some point

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

#135

Post by sathackr »

gelo wrote: post #127
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)?

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. Us…

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)

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

#136

Post by sathackr »

jacquesm wrote: post #124
sathackr wrote: post #110

Earlier quoted context omitted.

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 hea…

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? :-)

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

#137

Post by exabrial »

gelo wrote: post #127
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)?

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. Us…

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

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

#138

Post by gus_massa »

LesZedCB wrote: post #126
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…

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.

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

#139

Post by Florin_Andrei »

tyingq wrote: post #97
topspin wrote: post #45

Earlier quoted context omitted.

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…

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.
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