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Radios, how do they work?

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Re: Radios, how do they work?

#31

Post by scrlk »

rcxdude wrote: post #19
duped wrote: post #6

Earlier quoted context omitted.

And for those even deeper into the theory, one question you might ask is, if we can divide spectrum and time to get some bandwidth B per channel, how many bits can we send/receive over a distinct channel? The answer is C = Blog2(1 + S/N) where B is the bandwidth and S/N is the signal to noise ratio determined by the environment (how much noise is present relative to the signal being transmitted). The crazy thing is t…

Shannon was pretty ridiculous. He basically invented information theory, proved all the major theorems involved, and applied it to communications and error-correction codes. If you work in RF you can't do much without encountering his work. (It did take a while before anyone figured out how to get close in practice to the limits he proved, though)

And before his work on information theory, his master's thesis showed that Boolean algebra could be used to design digital circuits and invented logic gates:

https://en.wikipedia.org/wiki/A_Symbolic_Analysis_of_Relay_a...

https://spectrum.ieee.org/claude-shannon-information-theory

One of the all time greats.

Re: Radios, how do they work?

#32

Post by drmpeg »

somat wrote: post #24
Animats wrote: post #5

Earlier quoted context omitted.

> I was also delighted by the point about how all methods of modulating a wave can be recontextualized as frequency modulation! That's the classic way to think about it. Another way is to view the input as simply a sequence of voltage readings. Extracting a useful signal from that is an exercise in exploiting redundancy in noisy data. [1] Software defined receivers work that way. Analog radio (AM, FM, etc.) is a hulk…

I may not be understanding what part of the operation you are talking about. but radiated power? no transmitter had megawatts of radiated power. 50Kw for a fm broadcast antenna is a common number passed around. The huge "voice of america" shortwave station was 300Kw. I have heard of military radars having megawatts of radiated power. but even then it was in the low megawatts.

For UHF television stations, the effective radiated power (ERP) is typically 1 Megawatt. That is accomplished (for example) with a 57 kilowatt transmitter and an antenna with 12.44 dB gain.

Re: Radios, how do they work?

#33

Post by TrackerFF »

I think it is also worth mentioning the role of the ionosphere - which is the (charged) part of the atmosphere that will reflect radio/EM waves, and make it possible to communicate with someone on the other side of the globe. The ionosphere has different layers, and is quite dynamic - depending on the sun and its activity.

Basically, imagine a charged shell around the earth that reflects electromagnetic waves back, and that the properties of said shell is constantly fluctuating. Solar storms (and following northern lights) are bad news for radio communication.

That's the very, very ELI5 version.

Re: Radios, how do they work?

#34

Post by roelschroeven »

jayknight wrote: post #22

>A perfectly uniform waveform is still not useful for communications... It is if you encode information by switching it on and off in standard patterns. These uniform waveforms--or "continuous wave" (CW)--allow very simple devices with very little RF power to be used to communicate with Morse Code.

One could argue that technically it's no longer uniform if it's switched on and off, though.

Re: Radios, how do they work?

#35

Post by bitcharmer »

TrackerFF wrote: post #33

I think it is also worth mentioning the role of the ionosphere - which is the (charged) part of the atmosphere that will reflect radio/EM waves, and make it possible to communicate with someone on the other side of the globe. The ionosphere has different layers, and is quite dynamic - depending on the sun and its activity. Basically, imagine a charged shell around the earth that reflects electromagnetic waves back, a…

What's worth mentioning is that shortwave offers much lower transfer latency than optic fibre so it's possible to establish faster cross-continental communication over radio than trans-oceanic optic fibre cables.

Re: Radios, how do they work?

#36

Post by Aloha »

I work RF world pretty regularly, and I still consider the Superheterodyne Receiver to be tantamount to magic.

Edwin Armstrong was a brilliant brilliant man.

Re: Radios, how do they work?

#37

Post by jdietrich »

roelschroeven wrote: post #34
jayknight wrote: post #22

>A perfectly uniform waveform is still not useful for communications... It is if you encode information by switching it on and off in standard patterns. These uniform waveforms--or "continuous wave" (CW)--allow very simple devices with very little RF power to be used to communicate with Morse Code.

One could argue that technically it's no longer uniform if it's switched on and off, though.

It is no longer uniform. It's counter-intuitive (unless you've really internalised the Fourier transform and/or the Shannon-Hartley theorem) but a pure sine wave stops being a pure sine wave if you key it on and off and occupies progressively more bandwidth as the keying rate increases.

An even less intuitive result is that you can decode a signal that is weaker than the noise floor if the data rate is sufficiently low and/or the bandwidth is sufficiently high. This has practical applications in amateur modes like JT65, ultra-wideband communications and even GPS.

Re: Radios, how do they work?

#38

Post by [deleted] »

nonninz wrote: post #25

Their primer article [1] is also really nice. > Today, I’d like to close this gap with a couple of crisp definitions that stay clear of flawed hydraulic analogies, but also don’t get bogged down by differential equations or complex number algebra. Related: many, many years ago, when Facebook didn't exist yet, Google still passed as a "good" company, and hobbyist electronic geeks had almost only PICs to choose from, I…

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