Hi all: Why is it that we have a dozen or so different electromagnetic wave types and yet every one of them can be used for analog and digital communication?
Thanks!
In: Physics
Analog and digital are just interpretations of a signal. There isn’t anything special about the underlying wave.
It’s sort of like how sound can be used for different alphabets
The electromagnetic spectrum is continuous, we broke them up into “types” based on how different frequencies behave because it makes handling and discussing the concepts easier.
They all share the property that if you can emit and receive them in a structure way they can be used to communicate data. Thats as true for using visible light morse code as it is for high speed microwave transmissions. Digital vs analog is really just about how the emit/receive portion of that is happening, in particular the encoding and decoding of that data on either end.
they are all fundamentally the same type of wave. why wouldn’t you be able too?
you can even do both with other waves like sound waves. it has nothing to do with the wave, just how you define your signal. is signal existing 1, signal not 0? great its digital. is there an infinity varying gradient of possible variations at any given moment? great, its analog,
There aren’t really different types of electromagnetic waves, we’ve just arbitrarily split up the spectrum into frequency ranges. It’s kind of like how we categorize visible wavelengths as different colors, all usable for both paintings and writing letters, even though the spectrum blends them all together at the edges.
Sometimes the wavelength actually matters, for example if you’re trying to get the signal through walls or windows, or if you care about whether it will have enough energy to damage your body. But for the purpose of encoding a signal, they all work pretty much the same.
We don’t really have a dozen or so different electromagnetic wave types. Well we do, but only “on paper” if that makes sense. All electromagnetic waves are actually the same thing, except on different parts of one frequency spectrum. They’re just put into different “classes” because for practical reasons. The light coming out your screen right now is fundamentally the same thing as a wi-fi signal or an x-ray, except they obviously interact with the environment in different ways depending on where they are on that spectrum so they’re separated into different types for classification.
As for the communications thing, that’s beyond electromagnetism. Electromagnetism is just one medium out of many that you can use to transmit a signal. Analog or digital has nothing to do with the medium. You can use the vibrations of air molecules to transmit analog or digital signals. You can wave your arms to transmit analog or digital signals if you want. A clever arrangement of baked beans on the ground can encode analog or digital signals. What separates analog from digital is how the data is structured, not how it’s transmitted.
In some ways, all the electromagnetic waves are similar, and those properties are what we use for communications.
But different frequencies of EM interact with matter and our senses in very different ways, and it wasn’t always obvious that they were aspects of the same thing. Light we see with our eyes, radio we make and detect with electronics, x-rays show up in unexpected places and expose film. So we have different types of EM because they’re very different for most practical purposes, but all capable of carrying information.
Analogy: there are a lot of types of matter, but all of them can be used as a weight.
> Why is it that we have a dozen or so different electromagnetic wave types
What do you mean? There aren’t really different types of electromagnetic wave,, we just call them different things depending on the frequency. Radio waves are not fundamentally different from light waves, they’re just longer. As long as we have a way to produce electromagnetic waves of a given frequency, and a way to detect them at the other end, then we can use them for communication by modulating a signal onto them. The simplest way to do that is to just turn the signal on and off, like Morse code – but more sophisticated methods are usually used.
But there are some frequencies for which practical technologies don’t really exist. For example, there is also the so called “terahertz gap”, where we don’t really have practical technologies for generating radiation with frequencies of between 0.1-10THz (i.e, higher than microwaves but lower than infra-red light).
Also, at the [very low end of the spectrum](https://en.wikipedia.org/wiki/Extremely_low_frequency), the wavelengths get so long that you would need an enormous antenna to radiate significant power. While some nations have built enormous transmitter stations to communicate with their submarines (these waves are the only ones that can penetrate seawater), it’s not exactly practical. And at the very high end of the spectrum (X rays and gamma rays) the radiation is harmful, so we don’t use it for communication (not that it would be especially practical to do so either).
They’re not really different types. They’re the same thing on a continuous spectrum differing by only the frequency of which the wave occurs. The “types” are arbitrary divisions based on human applications. Visible light for example being what we see. Infrared being what temperatures on earth cause things to glow with. Radio waves being useful for electrical circuits. Xray for seeing through things. Nothing separates these. We don’t see UV, some animals do. Most things omit infrared from being hot, but turn you’ll stove on and you’ll see red come off. Your microwave oven and radio waves off your wifi router are actually the excat same thing, just very different power scales.
We can communicate with any of them, because all we do (and are fundamentally required to) with communication is vary the frequency a little to send a signal. Doesn’t matter if 10 kHz radio waves or 500 THz light, we can change the frequency a little in a pattern and send information with that.
The dumbest way is just pulse on and off. Basically, it’s a telegraph sending Morse code. We did this with radio waves in the past. And this is more or less what we do with fibre optics, we do not use the THz bandwidth efficiently yet.
There are more complicated ways too, that are way more bandwidth efficient. Bandwidth is literally the width of the frequency band you use. Make noise in the 50 to 450 Hz range to send your signal? That’s 400 Hz bandwidth. Make noise on the 10,000 to 10,400 Hz range to send your singal? Also using 400 Hz bandwidth. Switching on and off is very inefficient, as it makes a whole host of noise all over the spectrum.
FM is better. AM is even better, needing only twice the raw single bandwidth. Despite modulating wave height / amplitude, AM does use different frequencies too. E.g, if you send a 20 kHz audio signal (as that’s the range humans can hear), you’ll need 40 kHz of bandwidth with AM. That could be 40 kHz used on 100 kHz carrier (so 80 to 120 kHz needed). Thats why radio stattions carrier frequency (the station number) are spaced the way they are. Or it could be on 10 MHz, so 9.98 MHz to 10.02 MHz. Or it could be on a THz, we’re it’s a rounding error, basically. So, higher frequency do offer a LOT more capacity. There’s better than AM for techniques. For digital signals, we use things like QAM (quadrature amplitude modulation), which can hit 100% bandwidth efficiency.
We’ll probably never go beyond visible, at least not in the air. Why? UV, xray, and gamma rays are dangerous to us. And harder to make, control, and receive.
The “dozen or so different electromagnetic wave types” are still, ultimately, just that: electromagnetic waves. They’re all fundamentally the exact same thing, all travelling at the same speed (light), they just have different wavelengths/frequencies (wavelength and frequency are inversely proportional).
Electromagnetic waves are great for communications purposes because you’re not reliant on a physical medium to propagate the waves. They’re wireless!
Higher-frequency waves—from the top of the range of ultraviolet, up to gamma rays—are capable of ionizing atoms, which presents a risk to organic life. As such, we don’t use them for telecommunications. The lower-frequency parts of the spectrum we use for telecommunications, and we’ve carved them up into frequency bands for regulatory purposes, so that everybody can use them. The principles of how they can be used for telecommunications don’t differ though because, again: they’re all just electromagnetic waves. The principles in tuning into AM radio vs. microwave TV are essentially the same, you’re just “listening” to different frequencies of waves. (This is an extremely simplified summary; the intricacies of how an AM radio receiver and a television work are obviously very different in many ways.)
Electrons act like waves.
No they don’t, exactly.
They act like particles.
No they don’t, exactly.
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