| Both sides previous revisionPrevious revisionNext revision | Previous revision |
| hambasics:sections:waveinteraction [2024/11/24 12:54] – va7fi | hambasics:sections:waveinteraction [2025/08/29 16:25] (current) – [Effect on Communications] va7fi |
|---|
| * Note though that this particular animation only works if the laser is below the horizontal line. | * Note though that this particular animation only works if the laser is below the horizontal line. |
| |
| {{ggb>/howto/hambasics/sections/snells2.ggb 705,403}} | {{ggb>/hambasics/sections/snells2.ggb 705,403}} |
| |
| \$n_1\$ and \$n_2\$ are the [[wp>Refractive_index |Refractive Indices]] of the media. They are defined as the ratio of the speed of light in vacuum to the speed of light in the media \$\left(n = \frac{c}{v}\right)\$. For example, if \$n = 2\$, then the speed of light is twice as //slow// in the medium as it is in vacuum. The bigger \$n\$ is, the slower the speed. \$n = 1\$ means that the speed is the same as the speed of light in a vacuum. | \$n_1\$ and \$n_2\$ are the [[wp>Refractive_index |Refractive Indices]] of the media. They are defined as the ratio of the speed of light in vacuum to the speed of light in the media \$\left(n = \frac{c}{v}\right)\$. For example, if \$n = 2\$, then the speed of light is twice as //slow// in the medium as it is in vacuum. The bigger \$n\$ is, the slower the speed. \$n = 1\$ means that the speed is the same as the speed of light in a vacuum. |
| We'll talk about the effects of scattering on communications in more detail later because we need to see a few more basics first. But for now, we'll just say that a radio signal received through scattering will generally be weak, and suffer from rapid flutter or hollow sounding distortion. | We'll talk about the effects of scattering on communications in more detail later because we need to see a few more basics first. But for now, we'll just say that a radio signal received through scattering will generally be weak, and suffer from rapid flutter or hollow sounding distortion. |
| |
| It'll be weak because only a small portion of the energy reaches you (think of how much weaker the scattered light from the laser beam is compared to the what reaches the wall directly). And it'll be distorted because your antenna will be receiving the signal from multiple directions (radio wave-paths) at once (think of how you can see the green laser scattered by the mist as an extended line, instead of a single point). As we'll next, when a signal splits and takes different path (of different lengths), they recombined with a sort of "echo" can cause distortion. | It'll be weak because only a small portion of the energy reaches you (think of how much weaker the scattered light from the laser beam is compared to the what reaches the wall directly). And it'll be distorted because your antenna will be receiving the signal from multiple directions (radio wave-paths) at once (think of how you can see the green laser scattered by the mist as an extended line, instead of a single point). As we'll next, when a signal splits and takes different path (of different lengths), they recombined with a sort of "echo" that can cause distortion. |
| |
| |
| The first thing to notice is that when a wave reflects off a surface, it suffers a half-wavelength phase shift. This means that if the receiver is right next to the "mirror", the signal will cancel out. | The first thing to notice is that when a wave reflects off a surface, it suffers a half-wavelength phase shift. This means that if the receiver is right next to the "mirror", the signal will cancel out. |
| |
| {{ggb>/howto/hambasics/sections/multipath.ggb 700,300}} | {{ggb>/hambasics/sections/multipath.ggb 700,300}} |
| |
| If the receiver then moves away from the "mirror", the <fc #008000>reflected signal</fc> has to travel over a longer distance than the <fc #4682b4>direct signal</fc> before reaching the receiver. This means that phase between the two waves will change, sometimes cancelling each other, sometimes reinforcing each other. When the path difference (Δ) between the reflected and direct waves is a whole number of the wave length, the two waves cancel each other because of the half-wavelength difference from the reflection. But when the difference is a multiple of a half wavelength, the two waves add up constructively and the resulting signal is stronger. | If the receiver then moves away from the "mirror", the <fc #008000>reflected signal</fc> has to travel over a longer distance than the <fc #4682b4>direct signal</fc> before reaching the receiver. This means that phase between the two waves will change, sometimes cancelling each other, sometimes reinforcing each other. When the path difference (Δ) between the reflected and direct waves is a whole number of the wave length, the two waves cancel each other because of the half-wavelength difference from the reflection. But when the difference is a multiple of a half wavelength, the two waves add up constructively and the resulting signal is stronger. |
