4 ms·

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 c

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.

immibis 1y ago
The crystal radios I know don't have crystal oscillators - the word "crystal" refers to the diode.
- gtsnexp 1y ago
  https://www.youtube.com/watch?v=-GxL13rid1w https://www.youtube.com/watch?v=-GxL13rid1w
  - kragen 1y ago
    This is a video about the diode, in this case a Schottky diode made with a coil of copper wire filed to a fine point touching a piece of galena sitting loose in a bottlecap found by the side of the road. The video is notable for demonstrating the original "breadboard" technique, where you connect your wires and components by clamping them to a wooden board with the head of a wood screw. The book I learned the technique from recommended using a dished washer under the head of the screw so that the screw head doesn't push the wires sideways as you tighten it.
- dd_xplore 1y ago
  Perhaps I'm getting confused cuz this was long back. But I think it was a oscillator for sure...
pkolaczk 1y ago
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 can’t design a good filter with variable frequency. Enter the superheterodyne world. 7. Now finally got something that resembles a tunable AM radio, but it kinda whistles / hums a lot. Ah, so the mirror image is a real thing?! 8. Need a higher IF to be able to better reject the image before the mixer. Ok, let’s make a double conversion superhet then. 9. Buy a set of ceramic filters and play with them to get the best selectivity. 10. Try to add more amplification only to learn if you go too far you get an oscillator instead of an amplifier. 11. The sound level is not stable. Add AGC. 12. Pick up some stations from 5000+ km away. Nice. But there is some weird distortion. Oh, I’ve been a culprit of frequency selective fading… Fast forward and now I’m building a PLL synchronized AM product demodulator with a squaring loop for carrier recovery. Fun. Lot of fun! Wholeheartedly recommend!
- Aloha 1y ago
  I have used a synchronous AM detector once in a radio, its a game changer for listening to shortwave.
  - pkolaczk 1y ago
    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.
    - Aloha 1y ago
      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.
- jacquesm 1y ago
  > 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.
  - wingspar 1y ago
    Now I’m interested…
    - jacquesm 1y ago
      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://en.wikipedia.org/wiki/Crystal_detector https://rimstar.org/science_electronics_projects/razor_blade_diode_for_crystal_foxhole_radio.htm https://rimstar.org/science_electronics_projects/razor_blade... Good luck! And don't sneeze once you've found a good spot.
kragen 1y ago
Crystal radios don't normally contain crystal oscillators, which do require a battery source. Perhaps you mean a crystal rectifier.
- dd_xplore 1y ago
  Yeah perhaps I'm confused cuz this was long long back.

immibis 1y ago

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

gtsnexp 1y ago
https://www.youtube.com/watch?v=-GxL13rid1w https://www.youtube.com/watch?v=-GxL13rid1w
- kragen 1y ago
  This is a video about the diode, in this case a Schottky diode made with a coil of copper wire filed to a fine point touching a piece of galena sitting loose in a bottlecap found by the side of the road. The video is notable for demonstrating the original "breadboard" technique, where you connect your wires and components by clamping them to a wooden board with the head of a wood screw. The book I learned the technique from recommended using a dished washer under the head of the screw so that the screw head doesn't push the wires sideways as you tighten it.
dd_xplore 1y ago
Perhaps I'm getting confused cuz this was long back. But I think it was a oscillator for sure...

pkolaczk 1y ago

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 can’t design a good filter with variable frequency. Enter the superheterodyne world. 7. Now finally got something that resembles a tunable AM radio, but it kinda whistles / hums a lot. Ah, so the mirror image is a real thing?! 8. Need a higher IF to be able to better reject the image before the mixer. Ok, let’s make a double conversion superhet then. 9. Buy a set of ceramic filters and play with them to get the best selectivity. 10. Try to add more amplification only to learn if you go too far you get an oscillator instead of an amplifier. 11. The sound level is not stable. Add AGC. 12. Pick up some stations from 5000+ km away. Nice. But there is some weird distortion. Oh, I’ve been a culprit of frequency selective fading… Fast forward and now I’m building a PLL synchronized AM product demodulator with a squaring loop for carrier recovery. Fun. Lot of fun! Wholeheartedly recommend!

Aloha 1y ago
I have used a synchronous AM detector once in a radio, its a game changer for listening to shortwave.
- pkolaczk 1y ago
  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.
  - Aloha 1y ago
    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.
jacquesm 1y ago
> 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.
- wingspar 1y ago
  Now I’m interested…
  - jacquesm 1y ago
    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://en.wikipedia.org/wiki/Crystal_detector https://rimstar.org/science_electronics_projects/razor_blade_diode_for_crystal_foxhole_radio.htm https://rimstar.org/science_electronics_projects/razor_blade... Good luck! And don't sneeze once you've found a good spot.

kragen 1y ago

Crystal radios don't normally contain crystal oscillators, which do require a battery source. Perhaps you mean a crystal rectifier.

dd_xplore 1y ago
Yeah perhaps I'm confused cuz this was long long back.