For folks wondering why these sort of videos (there are lots on YouTube) always focus on AM towers:
1. On AM the radio energy literally pulses (the amplitude modulation) and thus the arcs of plasma will pulse too thus creating the audio noise. AM has a carrier wave that’s constant but the two sidebands of signal pulse from zero energy at silence to more power the louder the sound being transmitted. FM signals broadcast essentially the same power all the time since it’s the frequency and not the amplitude that’s changing.
2. Because the signal frequency is much lower on the AM broadcast bands the wavelength is much larger and thus the antennas are much bigger. On AM the tower itself is typically the antenna vs FM radio where the antenna is typically only a meter or two long at the top of a very tall tower. That’s what makes AM towers more dangerous as the tower can be carrying many kW of energy and if you touch it you’ll go zap zap. The towers typically sit on top of a ceramic insulator to insulate them from the ground whereas FM towers typically just are attached right to the ground (although with grounding straps for lightning protection).
Finally (some folks don’t always know this) you can operate AM on the frequencies typically used for FM… it’s just a mode and works on any frequency. Aviation radios operate on AM but in the VHF band near FM broadcast frequencies.
Another thing to note, since people seem to be focusing on the RF aspect of this: there's 20-30 Amps running to the tower in this video. If your body is the connection to ground for a 20 Amp current, from any source, you're going to have a lot more to worry about than a burnt pickle (I guess it's cool that you'd make radio sounds while you died?)
When they put the pickle/hotdog/whatever an inch away from the tower without actually touching it, it doesn't even get warm. This isn't RF, it's just standard-issue AC electrocution. Maybe the one "radio" thing here is that the ground underneath a tower like this is essentially a big metal mesh, but even that isn't a factor -- they're literally hooking a jumper cable from the pickle to ground.
RF burns are a lot different than electrocution-style burns, though. But I'm not an expert on either topic, I'd defer to some people who know more about it.
Definitely, but this video is not that.
Same disclaimer: I'm not an expert on this... but I have been talking a lot about RF burns and arcing with RF engineers, and I think there's more nuance to this.
It would be interesting to see the difference grounding a hot dog through 7 kW AC (60 Hz) and seeing any difference in internal heating and arcing. Maybe a topic to explore in another video—especially if I can get access to a transmitter manufacturer's testing lab...
Sure. I'm not trying to suggest that it isn't a factor at all, just that it's not what's ablating the hot hot dog/pickle in this example. I wouldn't want to sit next to a working AM tower and have lunch or anything.
Anecdotal: I was cooked by some pretty powerful ECM [electronics countermeasures] gear, because an ECM officer was dumb and had his equipment turned on while on the tarmac. My abdomen was up against the area where the antenna was, about 6 inches away.
No outward signs of injury, I just felt an internal burning sensation and severe nausea pretty quickly. I was feeling okay after about a day or two. I never did get checked out by medical, so no clue of what permanent damage was done.
Do you mean burning via resistive heat dissipation from current flow through flesh? There are also burns from plasma in arc discharge events. An arc discharge to the body can produce both.
I had no idea that radio towers used that sort of ampage.
I might be misremembering the tower (i.e. I might be remembering the amperage for a 50kW tower), but they definitely do.
Amperage on a 6kW tower will still be more than enough to kill you.
50 kW is a respectable AM station, while 6 kW is pretty short range.
16A on this full array, as measured by the RF ammeter feeding the phasor in the transmitter building.
Why would we want aviation radios to operate in AM? Is it just that we standardized on AM before the 60s, it works well enough, and migrating would require a worldwide effort? Or is there some interesting advantage to AM for planes? Maybe superior range?
AM doesn’t exhibit the capture effect, so you can hear multiple transmissions at once. https://en.m.wikipedia.org/wiki/Capture_effect
It's also possible to detect the presence of an AM transmission (if not necessarily decode) at a much lower received power than with FM. With FM there's little in the way of graceful degradation. As signal strength falls it can go from full fidelity to silence with very little transition.
This makes AM radio more fun to listen to, as you get knobs for both your radio and your mental “tuner”. At night, you can pretty consistently hear 3+ broadcasts at once, and listen to them all simultaneously a la overhearing many conversations at once in a busy room.
This one mostly. As otherwise mentioned, there is some advantage in the case of multiple transmissions at once for AM, but in practice both are often entirely garbled. The loud tone caused by any slight difference in transmit frequencies is the big indicator that something has gone wrong. If one signal is much stronger than the other then that tone will be very faint and will likely be missed. So AM has something like FM capture effect in that case.
AM has allowed for very narrow channels on the aviation band. In Europe mostly, the channels are only 8.33 kHz apart. Typical narrow band FM voice communication requires 12.5 kHz.
Since the end points in aviation are usually within line of sight of one another, radio communication is very easy. Any modulation method would work well. Of course in practice this means that the equipment is allowed to degrade that much more before anyone gets around to fixing it...
One reason is that AM signals blend together whereas with FM the stronger signal will tend to "capture" the others and be the only one heard. This matters a lot in busy airspace where multiple people may be talking simultaneously.
To answer you in a different way:
Today we would build these systems with FM or digital voice.
But there are enough advantages we've gotten used to (graceful degradation, better handling of doubling, etc...) that it's not really unequivocally a win to switch to FM. There would be downsides that anger existing users, and it would be expensive, and the net benefit would be relatively small.
Audio loudness is correlated to signal strength, so it is clear a very strong signal is from a source that is close, important to know in aircraft.
Two transmissions will produce a heterodyne (whine) due to the offset of carrier frequencies, so you hear both and the tone to know there are two transmitters. On FM, you’d hear only one, the strongest who captured your receiver.
The history of AM radio and the invention of the mechanical sparkgap transmitters by Reginald Fessenden is absolutely fascinating.
Imagine only having telegraphs and morse code and amateurs listening every night to the spark noises in morse then suddenly in 1906 (first done in 1900 !) you hear voices and music!
https://en.m.wikipedia.org/wiki/Reginald_Fessenden
can't seem to direct link the photos but scroll down to see what you are talking about with the base of the tower being a massive insulator
scroll to: Brant Rock, Massachusetts, facility
https://en.m.wikipedia.org/wiki/Reginald_Fessenden#Rotary-sp...
You can still see operating Alexanderson Alternators running at SAQ (Grimeton Radio Station). Not AM, but the same equipment was used for AM by Fessenden.
https://en.wikipedia.org/wiki/Alexanderson_alternator
https://www.youtube.com/watch?v=yYZjz745yGA