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Radios, how do they work?

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Re: Radios, how do they work?

#61

Post by chemeril »

pfdietz wrote: post #59

I'm intrigued by things like this that used to be high technology but now are mature and pushed way down into the infrastructure. No one is going to make much money being really good at radio, any more than they will be really good at machining steel, but it's still necessary for higher levels of the tech stack to function.

I promise people still make piles of money being really good at radio and really good at machining steel. The complexity of the deliverables has increased, yes, but the expertise and technical skill to do modern radio and machining is very much rewarded in the marketplace.

Re: Radios, how do they work?

#62

Post by jayknight »

jdietrich wrote: post #37
roelschroeven wrote: post #34

Earlier quoted context omitted.

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 l…

You can see it happening in! [1] is a waterfall display (time is vertical axis, frequency is horizontal) of a few CW signals and compare the harsh braodband clicks on the right to the nice dotted lines on the left. That kind of broadband noise happens when your signal goes from on to off too fast (or something else like just not generating a clean sine wave). If your radio can shape your keying to have a little ramp-up/ramp-down you get a much cleaner looking signal like those on the left.

The noise is effectively AM, since you are modulating the signal from 0 to full amplitude, and with the very fast amplitude change you get what looks like characteristic AM signal with a center carrier and symmetric sidebands.

[1] https://imgur.com/BnagQzb.jpg

Re: Radios, how do they work?

#63

Post by hilbert42 »

Aloha wrote: post #36

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.

Ha, not magic but conceptually the superhetrodyne is an absolutely brilliant design and it's still not lost is 'magic' even after a hundred years, and likely never will despite newer digital concepts (they being more complex to implement).

"Edwin Armstrong was a brilliant brilliant man."

Right! ...And as you'd likely know, Armstrong's tormentor and nemesis was an arrogant, despicable bastard of the first order!

(Believe it or not, but decades ago I worked in a prototype lab at RCA and actually met David Sarnoff albeit briefly. That never changed my opinion of him.)

Re: Radios, how do they work?

#64

Post by martinky24 »

pfdietz wrote: post #59

I'm intrigued by things like this that used to be high technology but now are mature and pushed way down into the infrastructure. No one is going to make much money being really good at radio, any more than they will be really good at machining steel, but it's still necessary for higher levels of the tech stack to function.

The US (and Chinese, and Russian, and European...) government spends billions a year on companies that are good at radio. Radar, satellite communications, 5G, etc, etc. are all critical parts of modern technology stacks, that are "high technology", and key for forward innovation. If you think it's a solved problem, why doesn't every telecom company have nationwide 5G deployed yet?

There is A LOT of money to be made in the space, if you're good.

But, it's not AdTech, so HN isn't familiar with the field I guess :^)

Re: Radios, how do they work?

#65

Post by nestes »

fourier54 wrote: post #57
entropicgravity wrote: post #48

For sure they do not work the way the "Path Loss Equation" would have you believe they do. The path loss equation violates conservation of energy ie the frequency or wavelength term depending on how it's structured cannot be in the equation. And the receiving antenna does not have any 'gain' other than physically getting bigger or smaller, though the transmitting antenna can have gain depending on shape and size. Tha…

How can an equation that does not represent a balance of energy violate energy conservation? With path loss equation I assume you refer to Friis equation which is just the ratio of power received at an antenna to power given to the transmitter. It is correct and does not violate conservation of energy since it says nothing about the power not received at the receiver

What they're saying is that the geometrical interpretation of an outwardly expanding spherical shell of power shouldn't depend on frequency. In this respect they are correct and they have a good intuition for the problem.

Now here's the catch: If the receive area were not changing as a function of frequency when the receive antenna gain is kept constant (it does), this would break physics (it doesn't). However, the effective area of an antenna with fixed gain varies as 1/lambda^2. In effect the geometric interpretation is still correct, but the variation of antenna area with gain resolves the seeming paradox and saves physics.

Re: Radios, how do they work?

#66

Post by hilbert42 »

Animats wrote: post #5
codyd51 wrote: post #2

This 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…

""…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."

Right. And modulation of any type produces sidebands as per Fourier! Do anything whatsoever to disturb a pure sine wave then math and physics dictates it so.

Re: Radios, how do they work?

#67

Post by hilbert42 »

pfdietz wrote: post #59

I'm intrigued by things like this that used to be high technology but now are mature and pushed way down into the infrastructure. No one is going to make much money being really good at radio, any more than they will be really good at machining steel, but it's still necessary for higher levels of the tech stack to function.

"No one is going to make much money being really good at radio, any more than they will be really good at machining steel,"

How do you know? For instance, I'd suggest that not every method of modulation has been invented or even yet implemented. Also, we've hardly begun to design and implement meta materials into antennae and RF filters—the field's still wide open for innovation and invention.

And new methods of 'machining' steel have recently been invented and are just coming into use (if I owned the patents I'd be sitting pretty for life).

Re: Radios, how do they work?

#68

Post by Isamu »

Also, I’m not sure if people are aware of the number of radio systems that enable their smartphones.

NFC (eg. Apple Pay) is a radio, range a few cm. Bluetooth is a radio, a few meters. WiFi is several radio systems, range tens of meters. Cell phone is several radio systems, range up to kilometers. GPS (and rival systems) range up to thousands of kilometers.

Re: Radios, how do they work?

#69

Post by threeio »

helsinkiandrew wrote: post #26

Tim 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. https://www.youtube.com/watch?v=LMxate9gegg

I can't recommend this entire series enough, Hunkin's work is a masterpiece.

Re: Radios, how do they work?

#70

Post by fourier54 »

nestes wrote: post #65
fourier54 wrote: post #57

Earlier quoted context omitted.

How can an equation that does not represent a balance of energy violate energy conservation? With path loss equation I assume you refer to Friis equation which is just the ratio of power received at an antenna to power given to the transmitter. It is correct and does not violate conservation of energy since it says nothing about the power not received at the receiver

What they're saying is that the geometrical interpretation of an outwardly expanding spherical shell of power shouldn't depend on frequency. In this respect they are correct and they have a good intuition for the problem. Now here's the catch: If the receive area were not changing as a function of frequency when the receive antenna gain is kept constant (it does), this would break physics (it doesn't). However, the e…

> the geometrical interpretation of an outwardly expanding spherical shell of power shouldn't depend on frequency

I think nobody says that is does. I believe the problem is to call Friis transmission equation "Free-space loss". Actually the Friis formula is composed of 3 terms: the receiving and transmitting antennas gain and the actual free space loss which has the 1/R^2 dependency (which actually isn't a "loss" in energy balance terms, since it's not lost energy, just energy not received at a certain point, so we could argue about that term too...)

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