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What happens when you touch a pickle to an AM radio tower

jeffgeerling.com

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Re: What happens when you touch a pickle to an AM radio tower

#51

Post by ryukoposting »

Supernaut wrote: post #27

What I didn't see explained in these videos, and which I'm now curious about, is the mechanism by which the hot dogs convert the radio signal into sound? I understand how a loudspeaker works, but since food products typically don't contain coils and magnets, how was the AM signal being demodulated and converted into sound waves?

I'm not an RF engineer, but I'll take a stab at it:

With any modulation scheme, you have the "carrier signal" and the "message signal." The carrier is the frequency you dial into your radio. The message is the thing you listen to - voice, music, whatever. Those two get "modulated" together and blasted out over an antenna, and ta-daa, radio!

Amplitude Modulation is really, really simple. It's literally just the product of the carrier signal by the message signal. The carrier signal is a really high frequency relative to the message, which is where I'm guessing the "resolution" of the signal comes from.

Now, hot dogs.

Hot dogs probably don't resonate very well. Or, maybe they do, but just a little bit at low-ish frequencies - up to a couple thousand Hertz, but no higher. If that's the case, then a hot dog would act like a low pass filter! Since AM is just the product of a high-frequency carrier and a low-frequency message, a low-pass filter could ostensibly leave behind something that resembles the message signal.

Proper AM demodulation involves diodes and whatnot, but I can't imagine a hot dog has semiconductive properties.

Now, if it's an electrical signal, why can we hear it through the hot dog? A hot dog is not a good antenna. It's bad at inducing an electromagnetic field around itself. Instead, it converts the energy from the radio tower into mechanical force - motion, like the way a speaker moves.

All of this could be wrong. Maybe the hot dog isn't serving as a filter, and it is indeed reproducing the AM carrier signal - it's just too high of a frequency for us to hear it. I don't remember my signal processing classes well enough to say for sure. Maybe my whole "hot dog is a speaker" explanation is bunk. Maybe hot dogs really are semiconductors. Not sure.

Re: What happens when you touch a pickle to an AM radio tower

#52

Post by fuzzfactor »

Supernaut wrote: post #27

What I didn't see explained in these videos, and which I'm now curious about, is the mechanism by which the hot dogs convert the radio signal into sound? I understand how a loudspeaker works, but since food products typically don't contain coils and magnets, how was the AM signal being demodulated and converted into sound waves?

The closer you are to the source of the radio waves, the less sensitivity will be needed in the receiver, and less audio gain you will need in your reproduction device.

And the less efficiency you will need in your speaker, aka transducer.

At these conditions there is also no more need for user-supplied power for the audio output to become audible, so no electronic amplification is needed.

As you get closer to the source the need for a carefully crafted, somewhat complex, receiver circuit will diminish, and when there is only one audio program being broadcast on a single radio frequency, no need to discriminate between different frequencies.

In an electronic radio, after the single radio frequency channel has been selected, then the radio frequencies are filtered out before electronic gain is applied to the audio alone. Otherwise audio power would be wasted amplifying radio frequencies that are not audible.

The hot dog emulates all of these requirements, except for the receiver sensitivity that would be needed to respond very strongly from a distance. No noticeable demodulation until it touches the source directly.

Then as a single-component device, a low-efficiency transducer, it conducts the full undemodulated RF power.

Its frequency response as a transducer is probably not even as high as human hearing can go, and people can not hear any RF being reproduced anyway, so all you hear is the audio.

Plus when it comes to hot dog conductivity, who could forget this futuristic home appliance from the 1960's:

Amy demonstrates the Presto Hot Dogger

https://www.youtube.com/watch?v=LMbQmp7yC-Y

Re: What happens when you touch a pickle to an AM radio tower

#53

Post by neilv »

BoxOfRain wrote: post #35

A soapbox of mine here in the UK is that since BBC and commercial AM radio is more or less dead with the remaining stations set to close over the next few years, Ofcom should open up the band to low-power broadcasting hobbyists. These already exist illegitimately and have done for decades, you can pick up plenty from the Netherlands and a few domestic ones as well on a sporadic schedule. It would be a nice thing to d…

Just yesterday, I was talking with a colleague in the UK, who's selling a serious-sounding amateur radio tower.

Whilst waiting for regulatory change, besides amateur radio station, are there other fun RF things one could do with such a tower's height?

Re: What happens when you touch a pickle to an AM radio tower

#55

Post by WarOnPrivacy »

bArray wrote: post #36
BoxOfRain wrote: post #35

A soapbox of mine here in the UK is that since BBC and commercial AM radio is more or less dead with the remaining stations set to close over the next few years, Ofcom should open up the band to low-power broadcasting hobbyists. These already exist illegitimately and have done for decades, you can pick up plenty from the Netherlands and a few domestic ones as well on a sporadic schedule. It would be a nice thing to d…

I think lots of communities running localised AM stations could be super cool. > There could be a minimal licencing regime to demonstrate the individual is not a complete numpty [..] I wouldn't bother and it just adds more resistance. > [..] and a fee to PRS for music rights along the lines of how streaming works. I think the quality is so low and the audience so few that it wouldn't matter. > Maximum power could be…

> I think lots of communities running localised AM stations could be super cool.

I agree. My US thoughts on the likelihood of (and potential outcome of) opening AM to the public - they all focus on content.

US AM content is mostly religious, conservative, sportsball and ethnic-usually-Latino. Those are the opposing interests to opening AM. To counter opposition, I'd open the upper half of the AM band to the public. To ease friction, I'd lift any regulatory fees and offer subsidies to offset costs.

As for content on the newly open bands, I could see at least 2 of the current AM interests firehosing cash to saturate the newly open bands and markets (which might unwind over the long term).

Re: What happens when you touch a pickle to an AM radio tower

#57

Post by geerlingguy »

neilv wrote: post #53
BoxOfRain wrote: post #35

A soapbox of mine here in the UK is that since BBC and commercial AM radio is more or less dead with the remaining stations set to close over the next few years, Ofcom should open up the band to low-power broadcasting hobbyists. These already exist illegitimately and have done for decades, you can pick up plenty from the Netherlands and a few domestic ones as well on a sporadic schedule. It would be a nice thing to d…

Just yesterday, I was talking with a colleague in the UK, who's selling a serious-sounding amateur radio tower. Whilst waiting for regulatory change, besides amateur radio station, are there other fun RF things one could do with such a tower's height?

Stick a meshtastic node at the top of the tower and be the envy of every meshtastic user!

Re: What happens when you touch a pickle to an AM radio tower

#58

Post by geerlingguy »

eternauta3k wrote: post #49
bjornsing wrote: post #26

A grounded pickle. The word grounded is very important here, and missing from the question in the title.

I wonder if a floating human would still get zapped, due to its non-trivial capacitance to ground.

Many tower climbers historically jumped onto AM towers (usually at lower power levels), and they still felt little shocks climbing the tower.

Even if the tower is off, if it's near any other sites, they can draw a significant amount of RF (as a good AM tower is a good AM antenna) and if it's not grounded, that RF will go through a person too!

This specific tower site doesn't require lights on the shorter towers, so it's not an issue here, but for sites with lights needing replacement, most nowadays turn off power to the tower and ground it before anyone climbs the tower.

Re: What happens when you touch a pickle to an AM radio tower

#59

Post by geerlingguy »

chadcmulligan wrote: post #43

you can light up fluorescent tubes as well https://youtu.be/SDL9O2Fwb64

We actually tried that experiment; the tubes we had were a little older, so not sure how much that affected it vs the power at this site (the middle tower is 7 kW, which is a lot less than the 50 kW towers at more mid/high power AM sites).

But it didn't light up near the tower. It did near the RF circuits above the phasor, though!

Re: What happens when you touch a pickle to an AM radio tower

#60

Post by ljf »

xattt wrote: post #33
ljf wrote: post #6

I mentioned over dinner at my parents house (about 20 years ago) that I'd read that running 240v through a gherkin would cause it to glow - and pretty much as soon as dinner was over, my father and I had the experiment set up. Gherkins and even pickled onions glowed brilliantly. I set up a basic site to share the video we'd taken and details of the experiment, and shared it to B3ta. Sadly all lost to time.

I see a similar comment at the end of the original article that mentions that pickles incandesce. Is it true incandescence or is it just internal arcing?

I wish I had the video still - maybe I need to run the experiment again, this time with my kids?

Tangent: I look back sometimes and realise how stupidly lucky I was to have a father who not only humoured my crazy ideas, but actively encouraged them - I only hope I am doing the same for my kids.

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