Antennas have always been black magic for me, and this article blew my mind with the "capacitor you pull apart". Thank you for posting this article, this is fantastic.
Radios, how do they work?
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Re: Radios, how do they work?
#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.
Re: Radios, how do they work?
#23Earlier quoted context omitted.
> divide that bandwidth by frequency (like AM and FM) or time Ah. The real magic is when we separate by space (beyond just frequency or time). The ability to do this was discovered relatively recently, in 1996, by a guy called Foschini, though radio astronomers will say "Meh". By adding multiple antennas and doing space-time coding engineers found they could pump an order of magnitude more data through a radio channe…
Fascinating how we keep being inspired by fundamental physics and astronomy to keep cramming mode information in our channels. I'm still trying to understand Orbital Angular Momentum multiplexing https://en.m.wikipedia.org/wiki/Orbital_angular_momentum_mul...
I'd agree with the Wikipedia article, that it sounds like MIMO, in that it requires the beam to have a spatial extent.
From the Wikipedia article:
> can thus access a potentially unbounded set of states
That's what people originally thought about MIMO. MIMO's not unbounded. The limit to the number of states is related to the surface area of the volume enclosing the antenna, with the unit of distance being the wavelength. A result radio astronomers already knew when the comms people derived it. With absolutely no evidence to back it up, I'd guess that the same limit applies to OAM multiplexing.
As an aside, when one expresses physics in terms of information theory my understanding is that the maximum the number of bits that can be stored in a volume of space (also the number of bits requited to completely describe that volume of space) is related to the surface area of the volume with the linear unit being Plank lengths. Is MIMO capacity in some way a fundamental limit in communications?
[1] https://physics.stackexchange.com/questions/497475/can-anyon...
Re: Radios, how do they work?
#24This is an excellent article, thank you for submitting it! I love how effortlessly this article delivered an intuition for why an ideal antenna length would be half of the wavelength of the signal you want to receive. I was also delighted by the point about how all methods of modulating a wave can be recontextualized as frequency modulation!
> 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.
Re: Radios, how do they work?
#25Their 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 found online a very long and complete electronic course that went from 0 to basic R/C concepts, to transistors, up to pretty advanced topics like magnets/transformers and IIRC radio too.
It was made of pretty raw HTML pages and images, and what was most peculiar about it was that it managed to explain a lot of concepts up to an applicable level (as in, actually designing analog circuits) without (any?) calculus at all.
Some of those may be false memories, but if I remember correctly:
* Its HTML style had a yellowy background * It was taken from an old-ish (US?) navy electric engineer-focused applied electronics course for training naval engineers. * It was more focused on analog circuits
I remember I downloaded it all but after all those years who knows where it could be. Maybe in some 1GB disk of my first Pentium PC, so it's basically lost.
Does anyone in HN knows what I'm talking about? I was never able to find it again.
[1] https://lcamtuf.substack.com/p/primer-core-concepts-in-elect...
Re: Radios, how do they work?
#26Tim Hunkin has posted a remastered version of his "The Secret Life of the Radio" TV program (from 1987) which recreates some of Hertz and Marconi's experiments with spark gaps and coherers.
Re: Radios, how do they work?
#27Antennas have always been black magic for me, and this article blew my mind with the "capacitor you pull apart". Thank you for posting this article, this is fantastic.
Not an RF engineer. But I mess with radio's for a living.
Most of the time when people try to explain antenna's they start talking resonance. Which really describes a 'good' antenna.
What an antenna does is create a alternating magnetic field with a alternating electric field 90 degress out of phase with each other. Blah blah blah quantum electrodynamics blah blah blah radiates photons.
Resonance means the antenna stores energy as resonance. That increases the electric and magnetic fields making the antenna radiate more efficiently. Some antenna's are very wide band and 'flat' and used for cough cough military cough cough and other applications.
Re: Radios, how do they work?
#28Their 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…
I guess the original "NEETS" content is this:
http://compatt.com/Tutorials/NEETS/NEETS.html
Content updated in 2011.
Re: Radios, how do they work?
#29Earlier quoted context omitted.
Under what circumstances is a diode and a capacitor enough to make a radio receiver?
AM peak detector is probably the easiest and primitive AM demodulator: it's basically made by a diode, a capacitor and a resistance. I implemented it when I was in the high school and I was making the first physics experiments. The idea behind this demodulator is quite easy: the diode filters out all of the negative part of the signal, then the positive signal charge the capacitor and the energy is released in a quit…
I was trying to say that a capacitor and diode (detector) is not a complete receiver.
Re: Radios, how do they work?
#30Earlier 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.
The goat testicle doctor did get permission for running his border blaster at a million watts.
https://en.wikipedia.org/wiki/John_R._Brinkley#Brinkley_and_...