Communication has always been of great importance for mankind. Just ask Paul Revere warning his fellow americans about the English attack; or Pheidippides who run all the way from Athens to Sparta to call for help, but the story was changed to make the poor Pheidippides to run from Marathon to Athens to deliver the news about the victory against Darius I (battle that his "little" son Xerxes would try to avenge against 300). Either way, being a victory or a cry for help, he died of exhaustion right after delivering the message. I wonder how much they would have paid for a cell phone. There is a lot to be said about communications in history but in this entry I'll try to combine science, technology and history and talk a little bit about the radio. However, it is not going to be a copy-paste of the wikipedia and, instead, I'll try to amuse you with several side-stories which will involve the Moon as a communication satellite, nazi propaganda, a radio without battery, the weather, submarines and headphones (Yes, the "iPod" was just to catch your attention ;-)).
Let us start with the crystal radio, the simplest radio ever with the interesting advantage of not requiring any battery. In fact, this radio is so simple (some wire, an inductance, a variable capacitor and a pair of earphones) that it was used by the prisoners inside the concentration camp depicted in the movie "Stalag 17" to get the news from the war. The antenna was a volleyball net. The reason for such a large antenna is both the range they tried to reach and the long wavelength of AM signal (1 to 10km).
But why this radio does not need any battery? Again, because of the AM signal. AM comes from Amplitude Modulation (demo video 1:24) which is a fancy name to say that the signal is multiplied and added to a tone, that is, a never-ending beep. The frequency of this tone is the carrier and is the one we try to tune with the variable capacitor (the dial of our old radios) to obtain the sound from the radio. If there are two radio emissions with very close carrier frequencies, then we get a mixture of both programmes and none of them good. Anyway, the thing is that, being AM broadcasting so simple, it is inefficient because the added carrier tone is also energy that it is not useful for the message. However, this tone can be reused to fuel the radio, hence avoiding the need for batteries. The idea is simple, if you have a look at the animation beside, you see that even though the signal on the top, which could be voice or a song, is disguised by the carrier, you can still recognise it in the resulting AM signal (in the middle). The thing is that, if the carrier has a large amplitude, that is, it is a "taller" wave with more energy, then it acts as an amplifier of the voice, which can be recovered by joining all the peaks of the wave.
We said that the radio was used by the prisoners, but it was used even more successfully by the nazis, as Hitler was the one who gave the great boost the radio needed to be the machine-in-every-home as the TV is today. This was called the people's radio (on the left) in contrast to the "people's car", otherwise known as Volkswagen. This radio was cheap because of component standardisation, heavily founded by the Nazi Party and was successfully used to convince the people from Saar (a small territory which belonged to France after the WWI) to voluntarily come back to be german territory. One "bug" of this cheap radio which turned to be a feature promoted by the party was that it could receive only local signals, therefore it could not tune foreigner signals and only to broadcast nazi propaganda. This, however, did not stop counter-attacking propaganda through other media. The people's radio was the ultimate brainwasher, cleverly illustrated by the telescreen of George Orwell's 1984. The British also had their own people's radio called utility radio but, in this case, the intention was to obtain more economic electronic components due to the massive sales to the people.
This is getting long and I haven't talked about half of what I promised. If you like it (and comment about it) I'll extend any of these stories in a second post but, for now, I'll give you the links to other related ideas. I wanted to talk about Earth-Moon-Earth communication where the Moon was used as a gigantic and cheap communication satellite, like a huge mirror where the signals are reflected. I also wanted to talk about Earth-mode communications, used for military and mining purpose where the signals is transfered through rocks and soil. Or how submarines have their own twitter with extremely low frequencies to tell them to rise and communicate when they are too deep to be reached by regular signals. Shortwave radios, which bounce against the ionosphere and can reach transoceanic communications were also in the menu and they were a good introduction point to tell you about how the weather, meteors, the aurora and even the day-night cycle affect these communications. It is also interesting the efforts of some governments to track and hunt down those amateurs that try to avoid censorship with this kind of radios. And, of course, I wanted to bring the active noise cancellation headphones we bought into the conversation. The following video (1:58) illustrate the theory and practice of this. Impressive.
Well, a lot was left to be said. I hope you found it interesting (the links are way better than this humble blog entry). If you like it, say so and comment what you liked the most (therefore I'll write more about related topics). Constructive insults (if it is possible such a thing) are also welcome. Hope to see you soon as I plan to write about how a crippled defeated the English Navy, a discussion about south-american revolutions and Avatar (Pocahontas not included, promise) and a cry for help for Google.
But why this radio does not need any battery? Again, because of the AM signal. AM comes from Amplitude Modulation (demo video 1:24) which is a fancy name to say that the signal is multiplied and added to a tone, that is, a never-ending beep. The frequency of this tone is the carrier and is the one we try to tune with the variable capacitor (the dial of our old radios) to obtain the sound from the radio. If there are two radio emissions with very close carrier frequencies, then we get a mixture of both programmes and none of them good. Anyway, the thing is that, being AM broadcasting so simple, it is inefficient because the added carrier tone is also energy that it is not useful for the message. However, this tone can be reused to fuel the radio, hence avoiding the need for batteries. The idea is simple, if you have a look at the animation beside, you see that even though the signal on the top, which could be voice or a song, is disguised by the carrier, you can still recognise it in the resulting AM signal (in the middle). The thing is that, if the carrier has a large amplitude, that is, it is a "taller" wave with more energy, then it acts as an amplifier of the voice, which can be recovered by joining all the peaks of the wave.
Well, a lot was left to be said. I hope you found it interesting (the links are way better than this humble blog entry). If you like it, say so and comment what you liked the most (therefore I'll write more about related topics). Constructive insults (if it is possible such a thing) are also welcome. Hope to see you soon as I plan to write about how a crippled defeated the English Navy, a discussion about south-american revolutions and Avatar (Pocahontas not included, promise) and a cry for help for Google.
Great entry! I really enjoyed it! All you've talked about is very interesting and I love the way you've connected such as different things. But I think a blog isn't long enough for u, u should write a book! :P
ReplyDeleteBTW, the noise cancelling headphones video is excellent
ReplyDeleteI always liked unbiased comments ;-) Anyway, I'm glad you liked it.
ReplyDeleteAbout the video and the links in general, I'm particularly proud of all my sources so, even if you didn't like the entry, the links are usually great.
Special mention to the first video, which is the full movie. A great way to honour the "sci" of sci-pr0n.
Interesting stuff but most of all very clever and amusing writing!
ReplyDelete'Ευγε!
Very interesting post!!
ReplyDeleteHad you read "Hornet Flight"? It's a nice Ken Follet book, that is related with your post.
PS: I'm sorry for my english (sometimes I think my mind is allergic to foreign laguages)
Thank you two! And no, I haven't heard about that book, I have to have a look at it. Thank you for the suggestion.
ReplyDeleteBTW, I'm running late for this week's entry, I'll try to publish it on Wednesday. Hope to see you there ;-)
I can't avoid to talk about another urban legend that tells the moon is a hollow artificial satellite built by 'whoknows'. The funny thing is the fact in that this legend is based. I had read it two years ago; They were using a new kind of sonar (not acoustic obviously, maybe we couldn't call it sonar...anyway..) focused on the moon trying to guess the inner moon structure and composition, but surprised, instead of get a clean an unique eco from each emission they get multiple and fading ecoes. As if the moon was hollow and this original eco bounced inside a metallic structure. Many newspapers talked about this new laughing at these scientists who ensured had discovered that the moon is in facth The Death Star from Star Wars.
ReplyDeleteJoin this legend with others about the radio communications of the apollo missions intercepted on earth by amateurs and you get the mother of all conspiracies.
Thank you for the touch of color to the post. I hadn't heard about the hollow Moon theory but, as any dialog between IT engineers, I had to consult the Wikipedia (http://bit.ly/bmpVFx). There, it tells several references to the literature where such theory is used in sci-fi books, but it also gives several scientific arguments against it. Anyway, we know Wikipedia does not have to be accurate nor veridical but, which I found more interesting is that such theory was also claimed about the Earth (http://bit.ly/aE1eRn) and we have a great example of it in the wonderful book: "A Journey to the Center of the Earth" (http://bit.ly/azmFpd).
ReplyDeleteSome other stories I've heard, probably more realistic ones, is that the Moon once collided against the Earth and it is the one to blame for our current rotation and deviation in the Earth's axis (that is, our magnetic pole is not our geographic pole). In fact, it is said that the orbit of the Moon is slowly speeding and decreasing and, in a far, far future, it will crash again against the Earth.
All the same, every Star Wars fan would find "comforting" to have a Death Star orbiting around us ;-)
I thought it was the opposite, the moon was moving away and some day in a far future it will leave geostationary orbit as a hammer thrown by an athlete. With all the consecuences like disappearance of tides, many people will change his behavior, some species of animals will disappear and probably a global tsunami caused by the suddenly fade out of the last tide in the last moment of moon gravity attraction.
ReplyDeleteRegarding the Death Star, some little an hairy people like me and Ewoks don't think the same about the safety of being watched by Darth Vader.