4 ms·

What Is Radio Spectrum?

55 points by ZunarJ5 3y ago

gr33nq 3y ago
Something I've had a longstanding desire to learn about is radio frequencies. I'm a very visual person, but I have yet to find any resource that explains it in a way that really makes sense to me. Especially when you start getting into modulation and whatnot. I'm fortunate to be able to use a variety of wireless technologies at work (licensed 80GHz, 18GHz and 950MHz frequencies), but I admittedly only have basic working knowledge and don't clearly comprehend what's happening at the lower physical level. Does anyone have a good recommendation on any material that really made wireless technology understandable for you?
- yabbs 3y ago
  One place to start peeling the onion is amature radio. In the US, see: https://www.arrl.org/ https://www.arrl.org/ Introduction to spectrum, freq allocation (bands) and modes.
- supertrope 3y ago
  It depends how far down you want to look. At the bottom is Maxwell's equations.
  - pierat 3y ago
    I thought that too, but things get weird when you try to separate 'electron-magnetism' and photonics. If you try to understand WHY a metal outer electron shell will shed a photon, you'll come up empty handed. And with electricity, the electrons move around from one side to the other. Except, do they? What exactly happens at an antenna interface? And why do we call it the EM spectrum, when the actual carriers are photons? It's the quantum-EM interactions that I think would make Maxwell's explanation why the equations work as they do make more sense. But even simple stuff in RF makes people evoke ideas of 'black magic'.
    - madengr 3y ago
      [dead]
- superkuh 3y ago
  There's no all in one stop for understanding radio but these 5 resources helped me a lot. The RF Get Down courses. This is by far the best material online to learn RF and how modulation works: https://www.youtube.com/@rfgetdown/videos https://www.youtube.com/@rfgetdown/videos 3blue1brown's video tutorial on the fourier transform: https://www.youtube.com/watch?v=spUNpyF58BY https://www.youtube.com/watch?v=spUNpyF58BY AT&T Archives: Similiarities of Wave Behavior http://www.youtube.com/watch?v=DovunOxlY1k http://www.youtube.com/watch?v=DovunOxlY1k Quadrature Signals: Complex, But Not Complicated by Richard Lyons, https://dspguru.com/files/QuadSignals.pdf https://dspguru.com/files/QuadSignals.pdf https://dspguru.com/dsp/tutorials/quadrature-signals/ https://dspguru.com/dsp/tutorials/quadrature-signals/ Antenna Theory's website and forums, https://www.antenna-theory.com/antennas/main.php https://www.antenna-theory.com/antennas/main.php I also highly recommend getting a $20 rtl-sdr USB software defined radio dongle. They're great toys for learning RF, what modulation is, and exploring the spectrum.
  - threeio 3y ago
    A 20$ RTL-SDR will give you a very broad view of the spectrum and an idea of how one area can be quiet, the other filled with signals and the oddities of atmospheric noise, etc. Super fun and there are 100,000 YouTube videos on how to get it working. https://www.amazon.com/NooElec-NESDR-Mini-Compatible-Packages/dp/B009U7WZCA/ https://www.amazon.com/NooElec-NESDR-Mini-Compatible-Package...
    - NikkiA 3y ago
      I would argue that a $0 web-sdr bookmark will teach you exactly the same things without you forever wondering if it's your antennae that's the problem.
      - furyg3 3y ago
        Where do you find these? Is there an online library?
        NikkiA 3y ago
- _whiteCaps_ 3y ago
  You might like: * https://www.sigidwiki.com/wiki/Signal_Identification_Guide https://www.sigidwiki.com/wiki/Signal_Identification_Guide * https://www.receiverbook.de/?type=openwebrx&band= https://www.receiverbook.de/?type=openwebrx&band=
  - i_am_a_peasant 3y ago
    awesome, I found an open websdr at the olympia tower in munich :)
- nickysielicki 3y ago
  https://youtu.be/DovunOxlY1k https://youtu.be/DovunOxlY1k https://youtu.be/-F7KYLO4Bkg https://youtu.be/-F7KYLO4Bkg https://youtu.be/ScOd3ExKFM8 https://youtu.be/ScOd3ExKFM8 https://youtu.be/I9m2w4DgeVk https://youtu.be/I9m2w4DgeVk
- pid-1 3y ago
  Download GNU Radio and implement modulation blocks by yourself. You can use it to simulate systems, without buying any hardware. You can write blocks in Python or C++. I don't recommend getting real hardware. Cheap software define radios will only work in uninteresting frequencies like AM / FM. You need way, way more expensive equipment to work with Wifi / 4G systems.
  - haswell 3y ago
    > Cheap software define radios will only work in uninteresting frequencies like AM / FM There’s quite a bit interesting stuff to listen to on cheap hardware. With a $20 dongle: - Local police/fire - Marine bands - Watch airplanes transmitting ADSB - Follow trunked radios in the area (more police depts are doing this) - Receive NOAA weather images - Pagers operate here, but legally this gets dicy Beyond this, addons like the Ham it Up upconverter can bring you Ham bands for a little more money and a lot more entertainment. And there’s a lot of other misc stuff to explore. Working with 4G systems is a whole other ball of wax anyway, and also gets into legally challenging territory. If the goal is to learn more about radio and find some interesting stuff going on in your area, a cheap dongle provides a lot of value and fun. I definitely can’t agree that this requires expensive equipment.
- rramadass 3y ago
  Hardware to play with: 1) HackRF : https://greatscottgadgets.com/sdr/ https://greatscottgadgets.com/sdr/ 2) RF Explorer : https://j3.rf-explorer.com/ https://j3.rf-explorer.com/ You also need to study Physics (Electromagnetics) and Electronics (Communication Electronics). Checkout both popular textbooks and general audience books. For a absolute beginner a good place to start is The Essential Guide to RF and Wireless by Carl Weisman.
Sporktacular 3y ago
It always bothered me seeing "ultrasonics" and "audible range" being listed in the same spectrum as microwaves and light. We can't hear it, audio is not part of the electromagnetic spectrum. They could mention submarine comms instead.
- lxgr 3y ago
  True, but on the other hand, you also can’t see VHF or microwave radiation! Yes, it’s a different medium, but for VLF/ELF, you could arguably just connect a photodiode/photoreceptor and a speaker/microphone to a very simple circuit and “hear/speak” that part of the spectrum, no?
  - Sporktacular 3y ago
    Our capacity to sense some frequencies, or build transducers or transceivers for them is a complication that's beside my point. Audio, including infra/ultrasonics does not belong in a diagram labelled The EM Spectrum. ELF, VHF, microwave and light etc. all do.
  - ale42 3y ago
    > you also can’t see VHF or microwave radiation! True, but you can definitely see some frequencies of electromagnetic radiation (light is electromagnetic radiation, just at a very large frequency). A 525 nm green LED is just emitting a signal at a frequency of 571 THz... which you can actually see. On the other hand, 40 kHz sound (ultrasound) and 40 kHz radio signals (LF, see https://en.wikipedia.org/wiki/Low_frequency https://en.wikipedia.org/wiki/Low_frequency) are definitely not on the same spectrum, one being made of changes in air pressure, the other one by an electromagnetic field.
- dredmorbius 3y ago
  The audio and EMR spectra may be different underlying phenomena, but for the purposes of radio, which transmits over EMR but encodes audio frequencies, the correspondence is significant. It's not possible to encode a higher-frequency signal over a lower frequency carrier, so radio frequencies which are used for the transmission of human-detectable sounds must be at a higher frequency than those sounds. I'm not nearly enough of a radio / audio / encoding geek to tell you what the minimum overage is, though I suspect it's at least 2x greater than the highest-frequency sounds that are intended to be encoded. For human-range hearing, that would be in the 10-20 kHz range, which would mean that a minimum carrier frequency would be somewhere around 20--40 kHz. The longest wavelengths used for voice comms so far as I know are the longwave or LW band, which is from 30–300 kHz, with the lower end of that pretty much precisely where I'd suggested it might be. Most commercial AM broadcasts are in the medium-wave (MW) band, from 531 kHz – 1602 kHz, or roughly 25-50x higher frequencies than the highest tones the human ear can detect. And I'd suspect that fidelity above 10kHz audio is not especially high even at those transmission frequencies. <https://en.wikipedia.org/wiki/AM_broadcasting#Broadcast_band_frequencies https://en.wikipedia.org/wiki/AM_broadcasting#Broadcast_band...>

55 points by ZunarJ5 3y ago

Something I've had a longstanding desire to learn about is radio frequencies. I'm a very visual person, but I have yet to find any resource that explains it in a way that really makes sense to me. Especially when you start getting into modulation and whatnot. I'm fortunate to be able to use a variety of wireless technologies at work (licensed 80GHz, 18GHz and 950MHz frequencies), but I admittedly only have basic working knowledge and don't clearly comprehend what's happening at the lower physical level. Does anyone have a good recommendation on any material that really made wireless technology understandable for you?

yabbs 3y ago
One place to start peeling the onion is amature radio. In the US, see: https://www.arrl.org/ https://www.arrl.org/ Introduction to spectrum, freq allocation (bands) and modes.
supertrope 3y ago
It depends how far down you want to look. At the bottom is Maxwell's equations.
- pierat 3y ago
  I thought that too, but things get weird when you try to separate 'electron-magnetism' and photonics. If you try to understand WHY a metal outer electron shell will shed a photon, you'll come up empty handed. And with electricity, the electrons move around from one side to the other. Except, do they? What exactly happens at an antenna interface? And why do we call it the EM spectrum, when the actual carriers are photons? It's the quantum-EM interactions that I think would make Maxwell's explanation why the equations work as they do make more sense. But even simple stuff in RF makes people evoke ideas of 'black magic'.
  - madengr 3y ago
    [dead]
superkuh 3y ago
There's no all in one stop for understanding radio but these 5 resources helped me a lot. The RF Get Down courses. This is by far the best material online to learn RF and how modulation works: https://www.youtube.com/@rfgetdown/videos https://www.youtube.com/@rfgetdown/videos 3blue1brown's video tutorial on the fourier transform: https://www.youtube.com/watch?v=spUNpyF58BY https://www.youtube.com/watch?v=spUNpyF58BY AT&T Archives: Similiarities of Wave Behavior http://www.youtube.com/watch?v=DovunOxlY1k http://www.youtube.com/watch?v=DovunOxlY1k Quadrature Signals: Complex, But Not Complicated by Richard Lyons, https://dspguru.com/files/QuadSignals.pdf https://dspguru.com/files/QuadSignals.pdf https://dspguru.com/dsp/tutorials/quadrature-signals/ https://dspguru.com/dsp/tutorials/quadrature-signals/ Antenna Theory's website and forums, https://www.antenna-theory.com/antennas/main.php https://www.antenna-theory.com/antennas/main.php I also highly recommend getting a $20 rtl-sdr USB software defined radio dongle. They're great toys for learning RF, what modulation is, and exploring the spectrum.
- threeio 3y ago
  A 20$ RTL-SDR will give you a very broad view of the spectrum and an idea of how one area can be quiet, the other filled with signals and the oddities of atmospheric noise, etc. Super fun and there are 100,000 YouTube videos on how to get it working. https://www.amazon.com/NooElec-NESDR-Mini-Compatible-Packages/dp/B009U7WZCA/ https://www.amazon.com/NooElec-NESDR-Mini-Compatible-Package...
  - NikkiA 3y ago
    I would argue that a $0 web-sdr bookmark will teach you exactly the same things without you forever wondering if it's your antennae that's the problem.
    - furyg3 3y ago
      Where do you find these? Is there an online library?
      - NikkiA 3y ago
_whiteCaps_ 3y ago
You might like: * https://www.sigidwiki.com/wiki/Signal_Identification_Guide https://www.sigidwiki.com/wiki/Signal_Identification_Guide * https://www.receiverbook.de/?type=openwebrx&band= https://www.receiverbook.de/?type=openwebrx&band=
- i_am_a_peasant 3y ago
  awesome, I found an open websdr at the olympia tower in munich :)
nickysielicki 3y ago
https://youtu.be/DovunOxlY1k https://youtu.be/DovunOxlY1k https://youtu.be/-F7KYLO4Bkg https://youtu.be/-F7KYLO4Bkg https://youtu.be/ScOd3ExKFM8 https://youtu.be/ScOd3ExKFM8 https://youtu.be/I9m2w4DgeVk https://youtu.be/I9m2w4DgeVk
pid-1 3y ago
Download GNU Radio and implement modulation blocks by yourself. You can use it to simulate systems, without buying any hardware. You can write blocks in Python or C++. I don't recommend getting real hardware. Cheap software define radios will only work in uninteresting frequencies like AM / FM. You need way, way more expensive equipment to work with Wifi / 4G systems.
- haswell 3y ago
  > Cheap software define radios will only work in uninteresting frequencies like AM / FM There’s quite a bit interesting stuff to listen to on cheap hardware. With a $20 dongle: - Local police/fire - Marine bands - Watch airplanes transmitting ADSB - Follow trunked radios in the area (more police depts are doing this) - Receive NOAA weather images - Pagers operate here, but legally this gets dicy Beyond this, addons like the Ham it Up upconverter can bring you Ham bands for a little more money and a lot more entertainment. And there’s a lot of other misc stuff to explore. Working with 4G systems is a whole other ball of wax anyway, and also gets into legally challenging territory. If the goal is to learn more about radio and find some interesting stuff going on in your area, a cheap dongle provides a lot of value and fun. I definitely can’t agree that this requires expensive equipment.
rramadass 3y ago
Hardware to play with: 1) HackRF : https://greatscottgadgets.com/sdr/ https://greatscottgadgets.com/sdr/ 2) RF Explorer : https://j3.rf-explorer.com/ https://j3.rf-explorer.com/ You also need to study Physics (Electromagnetics) and Electronics (Communication Electronics). Checkout both popular textbooks and general audience books. For a absolute beginner a good place to start is The Essential Guide to RF and Wireless by Carl Weisman.

Sporktacular 3y ago

It always bothered me seeing "ultrasonics" and "audible range" being listed in the same spectrum as microwaves and light. We can't hear it, audio is not part of the electromagnetic spectrum. They could mention submarine comms instead.

lxgr 3y ago
True, but on the other hand, you also can’t see VHF or microwave radiation! Yes, it’s a different medium, but for VLF/ELF, you could arguably just connect a photodiode/photoreceptor and a speaker/microphone to a very simple circuit and “hear/speak” that part of the spectrum, no?
- Sporktacular 3y ago
  Our capacity to sense some frequencies, or build transducers or transceivers for them is a complication that's beside my point. Audio, including infra/ultrasonics does not belong in a diagram labelled The EM Spectrum. ELF, VHF, microwave and light etc. all do.
- ale42 3y ago
  > you also can’t see VHF or microwave radiation! True, but you can definitely see some frequencies of electromagnetic radiation (light is electromagnetic radiation, just at a very large frequency). A 525 nm green LED is just emitting a signal at a frequency of 571 THz... which you can actually see. On the other hand, 40 kHz sound (ultrasound) and 40 kHz radio signals (LF, see https://en.wikipedia.org/wiki/Low_frequency https://en.wikipedia.org/wiki/Low_frequency) are definitely not on the same spectrum, one being made of changes in air pressure, the other one by an electromagnetic field.
dredmorbius 3y ago
The audio and EMR spectra may be different underlying phenomena, but for the purposes of radio, which transmits over EMR but encodes audio frequencies, the correspondence is significant. It's not possible to encode a higher-frequency signal over a lower frequency carrier, so radio frequencies which are used for the transmission of human-detectable sounds must be at a higher frequency than those sounds. I'm not nearly enough of a radio / audio / encoding geek to tell you what the minimum overage is, though I suspect it's at least 2x greater than the highest-frequency sounds that are intended to be encoded. For human-range hearing, that would be in the 10-20 kHz range, which would mean that a minimum carrier frequency would be somewhere around 20--40 kHz. The longest wavelengths used for voice comms so far as I know are the longwave or LW band, which is from 30–300 kHz, with the lower end of that pretty much precisely where I'd suggested it might be. Most commercial AM broadcasts are in the medium-wave (MW) band, from 531 kHz – 1602 kHz, or roughly 25-50x higher frequencies than the highest tones the human ear can detect. And I'd suspect that fidelity above 10kHz audio is not especially high even at those transmission frequencies. <https://en.wikipedia.org/wiki/AM_broadcasting#Broadcast_band_frequencies https://en.wikipedia.org/wiki/AM_broadcasting#Broadcast_band...>