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Radios, how do they work?

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Re: Radios, how do they work?

#71

Post by Isamu »

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…

>flawed hydraulic analogies

I want to say that’s cool, avoid common pitfalls in explanations, but I want to to point out that all analogies fall short, otherwise they would be the same thing, and not an analogy.

That is, if the hydraulic analogy were perfect, then that would mean that electronics would just behave as a fluid and we could teach it an a part of fluid dynamics.

But instead it is an analogy, electronics is not a part of fluid dynamics, there’s just a few similarities that can be used for teaching.

It’s not unusual to teach an imperfect simplistic model at first that you intend to supplement later with more details that break the analogy.

Re: Radios, how do they work?

#72

Post by jameshart »

> In today’s article, I’m hoping to provide an introduction to radio that’s free of ham jargon and advanced math.

Sounds great! Let’s dig in.

> … the fundamental mirroring behavior is still present, but it’s usually managed pretty well. Accidental mirror images of unrelated transmissions can be mitigated choosing the IF wisely, by designing the antenna to have a narrow frequency response, or by putting an RF lowpass filter in front of the mixer if needs be

Mission failed. Ah well.

Re: Radios, how do they work?

#73

Post by nestes »

fourier54 wrote: post #70
nestes wrote: post #65

Earlier quoted context omitted.

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…

Yep! Fully agreed with all your points, I was just trying to get at the original poster's line of thinking.

Re: Radios, how do they work?

#74

Post by IndrekR »

Isamu wrote: post #68

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.

NFC is not really a radio. Basically it uses a loosely copled transformer. Works much closer than 1 wavelength and only magnetic field matters.

Re: Radios, how do they work?

#75

Post by hilbert42 »

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…

"And the receiving antenna does not have any 'gain' other than physically getting bigger or smaller..."

Well, it depends on one's definition of gain! If you were to say to the designers of the ELT (the Extremely Large Telescope) that it had no gain over isotropic then they'd fall about laughing (remember, its method of operation also relies on collecting and concentrating incoming EM radiation as do RF antennae). An antenna's effective gathering aperture and directivity for both RX and TX is just about everything, and the coupling efficiency from the antenna to the feeder and RX/detector, and vice versa for the TX just about covers the rest.

"...though the transmitting antenna can have gain depending on shape and size."

Uh? How? What's the difference? Physics says the law of reciprocity applies, a good transmitting antenna also makes just as good a receiving antenna. The only proviso being that a transmitting antenna has to be designed to withstand high RF power levels (even then, this only applies to TX power levels where I²R losses can cause enough heating to damage the antenna and feed lines, similarly, high power TX levels can lead to very high voltages which can arc over; TX antennae are designed to handle this.)

I used to work with microwave transmitters and receivers and my microwave dishes and other types of antennae were directly interchangeable—in fact, they were identical.

Re the Path Loss Equation, it works in the practical sense and is used everywhere. Fighting over technicalities here is akin to arguing the difference between laws of motion under Newton and when they're subject to the rules of Einstein's Relativity. It's damn obvious when one's applicable and the other is not.

Re: Radios, how do they work?

#76

Post by dTal »

Isamu wrote: post #68

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.

...and yet, efficiently transferring a 1kb file between two physically adjacent smartphones remains an apparently unsolved problem.

Re: Radios, how do they work?

#77

Post by bigbillheck »

entropicgravity wrote: post #55
bigbillheck wrote: post #50

Earlier quoted context omitted.

> 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. Why is that?

It's because energy created by the transmitter must degrade as one over R squared in the far field. The frequency (or wavelength, have your pick) has nothing to do with the energy transmitted because energy must be conserved. Putting in the frequency term then violates conservation of energy between the antennas. Then, at the receiving antenna the error of conservation of energy is then patched up by assigning a bogu…

The formula on wiki has a distance squared term in the denominator tho?

Re: Radios, how do they work?

#78

Post by fourier54 »

IndrekR wrote: post #74
Isamu wrote: post #68

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.

NFC is not really a radio. Basically it uses a loosely copled transformer. Works much closer than 1 wavelength and only magnetic field matters.

100%. Every time I read the term "antenna" when referring to the coil used for NFC/RFID I suffer inside...

Re: Radios, how do they work?

#79

Post by hagbard_c »

jameshart wrote: post #72

> In today’s article, I’m hoping to provide an introduction to radio that’s free of ham jargon and advanced math. Sounds great! Let’s dig in. > … the fundamental mirroring behavior is still present, but it’s usually managed pretty well. Accidental mirror images of unrelated transmissions can be mitigated choosing the IF wisely, by designing the antenna to have a narrow frequency response, or by putting an RF lowpass…

Not really unless you refer to the use of 'IF' and 'RF'. Maybe it would have been better if they wrote these out as 'IF (intermediate frequency)' and 'RF (radio frequency)' with a link to explain in which context IF is used but for the rest that sentence looks OK to me.

Re: Radios, how do they work?

#80

Post by Aloha »

hilbert42 wrote: post #63
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! (Beli…

It was in part reference to "Any sufficiently advanced technology..."

So, you worked for RCA.. here is a question that there is no good book on, but what killed RCA, and what was it like working there?

I dont know what I think of Sarnoff - not sure I'd use evil - he was a "no niceties" fiercely competitive capitalist for sure - and how you feel about that may vary, Armstrong was also an extremely hard headed man, and thats not something that result in successful litigation - even if I am normally biased towards the underdog, he isn't always the most sympathetic underdog.

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