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Radios, how do they work?
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Re: Radios, how do they work?
#52Re: Radios, how do they work?
#53For 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…
That said, a receive antenna does absolutely have "gain", which is evident by the antenna receiving a stronger or weaker signal depending on its orientation with respect to the transmit antenna. The key is this: for an arbitrary antenna, the (transmit, if you like) gain has a one-to-one relationship to the "effective receive area" at a given frequency, so talking about area and gain are equivalent, if not intuitive. We usually assume for point-to-point links that the antennas are oriented at each other, and in such cases (for good aperture antennas), you are absolutely right that the physical area and effective area are approximately equal. For ideal wire antennas, however, the physical area of the antenna is 0, but the effective area is nonzero (because of magic).
Now, I disagree that the path loss equation violates conservation of energy. The link to the effective area and gain depends on the wavelength. When I increase the frequency of operation but I keep the gain of the antennas constant, the areas decrease, so my receive antenna is physically smaller and the power goes down. Not breaking physics. A lot of people will say "path loss gets worse as you go up in frequency", and this is extremely misleading if not "scientifically illiterate" as you pointed out. Sure, there are molecular absorption bands from oxygen/water that literally dissipate power in the atmosphere, but generally speaking, the path loss didn't get worse, your receive antenna just got smaller.
Now wait a minute, what if I just made my receive antenna larger? Well, you can do that! The problem is that because gain and area are linked, efficiently receiving power in a given LARGE area (with respect to the wavelength) implies high gain. High gain implies a very narrow beam (more like a laser pointer than a normal dipole spilling energy everywhere). So it becomes really important that I "point" my receive antenna perfectly at the transmitter. Satellite dishes are really big, and they absolutely have to be pointed accurately at the satellite.
Re: Radios, how do they work?
#54For 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…
> 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?
Re: Radios, how do they work?
#55For 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…
> 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?
Re: Radios, how do they work?
#56Earlier 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…
Where the "bogus" gain really shines, though: I can take my original receive antenna, operate it as a transmitter (so gain is now relevant), receive with my original transmit antenna (where I now care about area) and get the exact same result in terms of loss!
Re: Radios, how do they work?
#57For 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…
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
Re: Radios, how do they work?
#58I don't believe radiocommunications and the electronics of radio is hard to understand—at least that's so at a level where a hobbyist can gain enjoyment from the subject.
I say that as someone who obtained a radio amateur's license in junior highschool at age 15.
Yes, radio engineering and its physics does get very complicated at the high end, and for a good understanding one requires advanced math including partial differential equations such Maxwell's equations and their SR/Special Relativity extensions, and beyond that one needs to understand the physics of electrodynamics and that requires knowledge of quantum mechanics including QFT (Quantum Field Theory), which is top-echalon physics and close to as complex as physics gets.
However, the hobbyist doesn't need to know an iota of that advanced complex stuff to enjoy radio as a hobby. Absolutely none of it.
All that he/she needs to know are very basic principles such as how antennas receive and radiate signals, how radio signals are amplified and detected, and later on how signals are mixed, multiplied and hetrodyned, and how radio transmitters and receivers work—even the principles behind how the common superhetrodyne receiver works is pretty standard knowledge for a radio hobbyist.
Back when I was learning about radio I doubt very much if an article would have been written in the tone of this story, especially so one that implied that to understand the subject could be difficult even at a hobby level. Why, you may ask? Well back then, if anyone had a hobby interest in electricity and electronics then essentially the only outlet for their interest was radio and perhaps television, as the other branches of electronics would not have been as readily accessible to hobbyists.
Nowadays, that's changed, there's much more to keep a hobbyist's interests such as programming, computers, computer games, and other electronics not based on radio technology—digital electronics for instance, so knowledge about radio tech and radiocommunications theory have become much less commonplace having been diluted amongst all these competing interests. Obviously, the knowledge is still out there but it's more widely dissipated and not as easily accessible in the practical sense, especially so for hobbyists of a young age.
When radio was essentially all that there was around there were many more elementary books on radio available for younger readers and these increased in complexity as the hobbyist gained practical experience. For instance, when I first became interested in radio my first introduction to the subject—like most others—was building crystal set radios, and from there we advanced to incorporating tubes and transistors into our more advanced designs. For beginners, hands-on practical books such as how to build crystal sets which included many different designs were commonly available.
(Back then, a well known author of books on crystal sets and basic radio was Bernard B. Babani, an unforgettable name if ever there was one. His books are still available but you'd never know to look for them unless told about them.)
Today, many have never heard of crystal sets let alone their 'cats' whisker' detectors, so when they become interested in the subject they're thrown in at the deep end. And not having the basics already under their belts, the more advanced radio theory comes as a bit of a shock.
Re: Radios, how do they work?
#59Re: Radios, how do they work?
#60For 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…