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Radios, how do they work? (2024)

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Re: Radios, how do they work? (2024)

#61

Post by kragen »

anthomtb wrote: post #60
kragen wrote: post #42

Earlier quoted context omitted.

This is basic math, not advanced math. If you don't know it, don't worry, you can learn it pretty quickly. Maybe watch some 3Blue1Brown videos and do some textbook exercises and/or game programming. Git gud. There is no royal road to radio modulation. I learned that subtraction was the same as adding a negative number sometime around second grade, and I learned (then forgot) the trigonometric angle-sum identities in…

> Euler's formula So much EE-related math becomes trivial (or at least not-hard) once you've internalized this formula. What I am trying to decide is 1) Did I zone out in class when Euler's formula was introduced or 2) Did my secondary school mathematics classes just kind of gloss over it? I lean towards 2 but unfortunately none of my college classes reintroduced the formula and I ended up making a lot of problems ha…

I'm not sure any of my secondary-school classes taught it, but I dropped out of secondary school to go to the university, so maybe they would have in the following year. In secondary school I was in the "smart kids" math track, though, and they also had an "average kids" track and a "dumb kids" track, and I really doubt those tracks covered it.

Re: Radios, how do they work? (2024)

#62

Post by tonymet »

This is a great review, but don't let theory interfere with practice. There's an art and feel to radio and antenna building. I've built antennas with scrap wire and baluns without double checking . Just a rough length of wire tweaked until you hear someone.

The theory seems overly complex (because it is). but for practical radio you can tune up nearly anything and chat -- and be way more productive with it.

Imagine obsessing over the mechanics of baseball or fishing without ever tossing a ball or casting a reel.

Re: Radios, how do they work? (2024)

#63

Post by jacquesm »

wingspar wrote: post #58
jacquesm wrote: post #53

Earlier quoted context omitted.

> You can use a germanium diode or even Shottky now instead of a “crystal”. Or a razor blade or a piece of roofing lead and a needle.

Now I’m interested…

Diodes occur naturally, all you need to do is find them!

Good places to look for them are conductors and crystals.

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

https://rimstar.org/science_electronics_projects/razor_blade...

Good luck! And don't sneeze once you've found a good spot.

Re: Radios, how do they work? (2024)

#64

Post by mickduprez »

whartung wrote: post #55
pkolaczk wrote: post #14

Earlier quoted context omitted.

You can use a germanium diode or even Shottky now instead of a “crystal”. Such a simple radio can be a gateway drug to a very complex and deep hobby. In my case it went like that: 1. Built a simple radio 2. Could hardly hear anything, need to add an amplifier to it 3. Now it’s better but captures a lot of noise 4. Design a filter to select just that one station 5. Now I want to listen to more stations. 6. Ugh, you ca…

There's something to note here. As someone who's always dabbled in electronics, skimmed and read some books, my primary complaint abot most electronics texts is that they just talk about individual topics: oscillators, amplifiers, etc. What they never talk about, is putting them all together. But as witnessed by this list, that's what a radio is. A collection of these "meta" components into a whole to get a better ra…

"A radio built like this, with individual subsystems connected together, is much more understandable."

Yes! this has been my experience too, building something from first principles and given some tools and direction to experiment you get the chance, and experience, to really learn. I've been looking for resources like this for building amps but they're either small signal or the whole design. You understand how they work but not where and what to change if you wanted to tinker or build your own.

Re: Radios, how do they work? (2024)

#65

Post by peterfirefly »

jacquesm wrote: post #63
wingspar wrote: post #58

Earlier quoted context omitted.

Now I’m interested…

Diodes occur naturally, all you need to do is find them! Good places to look for them are conductors and crystals. https://en.wikipedia.org/wiki/Crystal_detector https://rimstar.org/science_electronics_projects/razor_blade... Good luck! And don't sneeze once you've found a good spot.

> Diodes occur naturally, all you need to do is find them!

Even true for LEDs!

https://en.wikipedia.org/wiki/Silicon_carbide#Natural_occurr...

https://en.wikipedia.org/wiki/Light-emitting_diode#History

Re: Radios, how do they work? (2024)

#66

Post by akvadrako »

royskee wrote: post #59
jandrese wrote: post #35

Earlier quoted context omitted.

As I understand it General gets you most everything and Extra is mostly useful for people who want to teach amateur radio classes.

Huh, I never heard that one. Extra gets you more frequency privileges (nice not having to worry so much about band edges) but IMO the real benefit is being able to enjoy reciprocal operating under CEPT when traveling abroad.

You can operate abroad with General in most countries.

Re: Radios, how do they work? (2024)

#68

Post by Aloha »

pkolaczk wrote: post #56
Aloha wrote: post #50

Earlier quoted context omitted.

I have used a synchronous AM detector once in a radio, its a game changer for listening to shortwave.

Oh, thanks, good to know. Now I feel more motivated. Because actually it’s not as easy as it looks from the text books. It’s like with drawing an owl. Yeah, pass the signal through a mixer and feed recovered carrier to its LO port and you’re done. Sure. Simple. Now just recover the carrier. So far I have built a PLL that locks to a clean signal but stops locking when the signal is modulated too much. Aargh.

I wish it was easier to buy a portable radio with one. Though admittedly I tend to use mostly vintage radios - as such I do most of my shortwave listening on a Zenith T-O which is pretty wonderful both in audio quality and capacity to pull in stations.

Re: Radios, how do they work? (2024)

#69

Post by mikewarot »

If you dig deeper, you end up with I/Q signals. If you take the input from the antenna and delay it by 90 degrees, you then have something which can have a positive or even negative frequency. Using multiplication of complex terms, you can add or subtract frequencies without generating unwanted images.

You could also use signals from 2 antennas 90 degrees apart to get I and Q. This gives you the added ability in that signals from one side has a negative frequency. It's some really useful stuff.

Re: Radios, how do they work? (2024)

#70

Post by dd_xplore »

immibis wrote: post #10
dd_xplore wrote: post #9

To get an idea about radios, I made a crystal radio when I was in 7th grade, I only had few components. The only component I had difficulty in getting was the crystal oscillator (I was living in a rural town). It was mind blowing when I first heard the audio through IEMs ! It felt magical that this contraption was working without any battery source.

The crystal radios I know don't have crystal oscillators - the word "crystal" refers to the diode.

Perhaps I'm getting confused cuz this was long back. But I think it was a oscillator for sure...
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