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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 m
by JCM9 2y ago
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.
- timr 2y agoAnother 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.
- geerlingguy 2y agoRF 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.
- MisterTea 2y ago> electrocution-style burns 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.
- timr 2y agoDefinitely, but this video is not that.
- geerlingguy 2y agoSame 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...
- timr 2y agoSure. 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.
- runjake 2y agoAnecdotal: 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.
- hermitcrab 2y agoI had no idea that radio towers used that sort of ampage.
- timr 2y agoI 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.
- geerlingguy 2y ago16A on this full array, as measured by the RF ammeter feeding the phasor in the transmitter building.
- pclmulqdq 2y ago50 kW is a respectable AM station, while 6 kW is pretty short range.
- ck2 2y agoThe 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 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-spark_transmitter_and_the_first_two-way_transatlantic_transmission https://en.m.wikipedia.org/wiki/Reginald_Fessenden#Rotary-sp...
- jhallenworld 2y agoYou 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://en.wikipedia.org/wiki/Alexanderson_alternator https://www.youtube.com/watch?v=yYZjz745yGA https://www.youtube.com/watch?v=yYZjz745yGA
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- Johnythree 2y agoYou have it backwards: Fessenden is famous for developing a electomechanical RF generator which put out a clean sinewave (eg a coherent wave), which helped replace the earlier Spark-Gap systems (which generated wide-band hash).
- CobrastanJorji 2y agoWhy 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?
- K7PJP 2y agoAM doesn’t exhibit the capture effect, so you can hear multiple transmissions at once. https://en.m.wikipedia.org/wiki/Capture_effect https://en.m.wikipedia.org/wiki/Capture_effect
- gwbas1c 2y ago> The ability to receive multiple signals simultaneously is in some cases considered beneficial and is one reason that the aviation industry, and others, have chosen to use AM rather than FM for communications.
- retrac 2y agoIt'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.
- dumbo-octopus 2y agoThis 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.
- nsxwolf 2y agoOne 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.