5 ms·

Careful you might have to explain inverse-square law.

by SigmundA 5y ago

dragontamer 5y ago
Radio is emitted in 3-dimensions, right? So its inverse-cube law?
- ncmncm 5y ago
  No.
- ajb 5y ago
  The dilution factor is the surface of sphere centered at the emitter, not the volume of the sphere. EM radiation is not like gas diffusion.
  - dragontamer 5y ago
    Appreciated. That explanation makes a lot of sense. EDIT: I also know we aren't dealing with "spheres", but... I get the gist. Dipole antenna emits in this weird doughnut shape, but as a 3-dimensional object, we can estimate it to be kinda-sorta like a sphere :-)
    - ajb 5y ago
      Certainly their surface areas are both O(r^2) :-) Actually though, I think a sphere is still in a way the right object. The weird donut is a representation of the amount that is emitted in different directions - I guess it's a contour of equal intensity. But the radiation is still emitted at the speed of light in every direction. So the wavefront at any given time is a sphere (until it is defracted or reflected). (Edited to add) unless you're thinking of a really big dipole, so you can't treat it as a point source? Or close to it.
      - dragontamer 5y ago
        Hmmm. > But the radiation is still emitted at the speed of light in every direction. I think that makes sense. > (Edited to add) unless you're thinking of a really big dipole, so you can't treat it as a point source? Honestly, didn't think of that issue either. You're right though, some antennas (especially AM antennas) are the size of Godzilla, and its absurd to even think of them as point-sources.
        SigmundA 5y ago
        No antenna is a perfect point omni emitter, the weird non spherical shapes like doughnuts is the antennas gain, almost are antennas are somewhat directional, the shape is a plot of the measured radiation around the antenna. You take advantage of the fact that it radiates more to the sides than up and down and orient that so it putting more power to the horizon rather than up into space (for terrestrial transmission). The term gain is just referring to the antennas directionality relative to a perfect spherical omni radiator that doesn't exist.

Careful you might have to explain inverse-square law.

dragontamer 5y ago

Radio is emitted in 3-dimensions, right? So its inverse-cube law?

ncmncm 5y ago
No.
ajb 5y ago
The dilution factor is the surface of sphere centered at the emitter, not the volume of the sphere. EM radiation is not like gas diffusion.
- dragontamer 5y ago
  Appreciated. That explanation makes a lot of sense. EDIT: I also know we aren't dealing with "spheres", but... I get the gist. Dipole antenna emits in this weird doughnut shape, but as a 3-dimensional object, we can estimate it to be kinda-sorta like a sphere :-)
  - ajb 5y ago
    Certainly their surface areas are both O(r^2) :-) Actually though, I think a sphere is still in a way the right object. The weird donut is a representation of the amount that is emitted in different directions - I guess it's a contour of equal intensity. But the radiation is still emitted at the speed of light in every direction. So the wavefront at any given time is a sphere (until it is defracted or reflected). (Edited to add) unless you're thinking of a really big dipole, so you can't treat it as a point source? Or close to it.
    - dragontamer 5y ago
      Hmmm. > But the radiation is still emitted at the speed of light in every direction. I think that makes sense. > (Edited to add) unless you're thinking of a really big dipole, so you can't treat it as a point source? Honestly, didn't think of that issue either. You're right though, some antennas (especially AM antennas) are the size of Godzilla, and its absurd to even think of them as point-sources.
      - SigmundA 5y ago
        No antenna is a perfect point omni emitter, the weird non spherical shapes like doughnuts is the antennas gain, almost are antennas are somewhat directional, the shape is a plot of the measured radiation around the antenna. You take advantage of the fact that it radiates more to the sides than up and down and orient that so it putting more power to the horizon rather than up into space (for terrestrial transmission). The term gain is just referring to the antennas directionality relative to a perfect spherical omni radiator that doesn't exist.