What is Propagation: Definition and 487 Discussions
Radio propagation is the behavior of radio waves as they travel, or are propagated, from one point to another, or into various parts of the atmosphere. As a form of electromagnetic radiation, like light waves, radio waves are affected by the phenomena of reflection, refraction, diffraction, absorption, polarization, and scattering. Understanding the effects of varying conditions on radio propagation has many practical applications, from choosing frequencies for international shortwave broadcasters, to designing reliable mobile telephone systems, to radio navigation, to operation of radar systems.
Several different types of propagation are used in practical radio transmission systems. Line-of-sight propagation means radio waves which travel in a straight line from the transmitting antenna to the receiving antenna. Line of sight transmission is used for medium-distance radio transmission, such as cell phones, cordless phones, walkie-talkies, wireless networks, FM radio, television broadcasting, radar, and satellite communication (such as satellite television). Line-of-sight transmission on the surface of the Earth is limited to the distance to the visual horizon, which depends on the height of transmitting and receiving antennas. It is the only propagation method possible at microwave frequencies and above.At lower frequencies in the MF, LF, and VLF bands, diffraction allows radio waves to bend over hills and other obstacles, and travel beyond the horizon, following the contour of the Earth. These are called surface waves or ground wave propagation. AM broadcast stations use ground waves to cover their listening areas. As the frequency gets lower, the attenuation with distance decreases, so very low frequency (VLF) and extremely low frequency (ELF) ground waves can be used to communicate worldwide. VLF and ELF waves can penetrate significant distances through water and earth, and these frequencies are used for mine communication and military communication with submerged submarines.
At medium wave and shortwave frequencies (MF and HF bands) radio waves can refract from the ionosphere. This means that medium and short radio waves transmitted at an angle into the sky can be refracted back to Earth at great distances beyond the horizon – even transcontinental distances. This is called skywave propagation. It is used by amateur radio operators to communicate with operators in distant countries, and by shortwave broadcast stations to transmit internationally.In addition, there are several less common radio propagation mechanisms, such as tropospheric scattering (troposcatter), tropospheric ducting (ducting), and near vertical incidence skywave (NVIS) which are used in specialized communication systems.
Hi!
I am dealing with the propagation of electromagnetic emissions through the atmosphere. To quickly outline:
Imagine some charge distribution flying at relativistic speeds and inducing a four-potential A. We define some retarded time at which the charges are at some positions, and calculate...
good morning I have a small problem, so can a low frequency 20 - 40 khz ultrasound beam pass through 60 cm of "air" and then 3 cm of bone? Considering the low frequency of ultrasound in this case it is possible
Hi,
I know in todays world we have more sophisticated equipment to measure the propagation delay of electronics equipment, but for my own curiosity i want to know how historically the propagation delay was measured for electronics device such as transistor.
I am a bit confused on the speed of voltage propagation in the transmission line and I hope someone can enlighten me. I understand the speed of voltage propagation is in the same order as the speed of light and it is much faster than current. But if we can model the transmission line with a...
According to Einstein light would be a particle and a wave.
So I infer that it propagates in vacuum in form of waves of little bullets (particles).
This explanation is very insuficient.
So tell me how do waves increase in size since it's made of little bullets (particles)... a wave gets...
Hi, I've been struggling for a long time to understand the propagation of light. Here are my key problems:
- since a star can be seen from any direction, it means that photons are emitted in all these directions, which are infinite, how is this possible? infinite photons?
- in case there are...
I understand how to compute and propagate errors but have trouble with conceptualizing all things put together.
I have performed an experiment to determine a value for some quantity. This quantity depend on two variables. The first one depend in turn on some other quantities as well but I think...
I guess it is safe to say that SR is, mathematically speaking, a framework that correlates discrete events in spacetime by way of a universal constant (the speed of light) so that the "proper distances" that separate them may be determined. I think this means that every conceivable "instant...
I was imagining trying to construct a rectangle of area ##A = xy##
If we give a symmetric error to each dimension ##\epsilon_x, \epsilon_y##
$$ A + \Delta A = ( x \pm \epsilon_x )( y \pm \epsilon_y )$$
Expanding the RHS and dividing through by ##A##
$$ \frac{\Delta A}{ A} = \pm...
Hello, people say that light has properties of particles and waves. Ok, but how exactly?
We have the principle of rectilinear propagation of light as a law on Physics. Light would be a particle that propagates in a direct line pointed to all directions with origin on the source of light.
The...
Hi, there. I am currently reading the paper, Gravitational Faraday rotation induced by a Kerr black hole (https://doi.org/10.1103/PhysRevD.38.472). After Eq. (2.4), it reads that
The paper does not provide the derivation of the equations and no related reference is listed. Also, ##k^i## is not...
Imagine two electro-magnets about a metre apart aimed at each other. We turn one of them on, and are able to watch the magnetism propagate in slow motion. The moment the magnetism reaches the second electro-magnet, we turn this on (in a manner in which it attracts), and turn the first one...
Hello! I am a bit confused about how to interpret symmetric error when doing error propagation. For example, if I have ##E = \frac{mv^2}{2}##, and I do error propagation I get ##\frac{dE}{E} = 2\frac{dv}{v}##. Which implies that if I have v being normally distributed, and hence having a...
Hello,
I need help with making sure I am using instrumentation error analysis correctly through an experiment in which I verify Ohm’s Law for a simple circuit. I do have a few questions below. I calculated and measured the error two different ways and did not get the same error by both methods...
I'm making a MATLAB code to propagate a gaussian field in the angular spectrum regime (fresnel number >> 1).
After Fourier transforming the field, you propagate it: $$U(k_x,k_y,z) = U(k_x,k_y,0)e^{ik_z z}$$
The thing that I am having trouble with is the propagation factor, I have looked at this...
Hi alltogether,
I have been confused about a certain topic of EM wave propagation:
it´s clear to me that E and M field are perpendicular to each other (I know Maxwell´s equations well).
But:
sometimes you can find on the internet that both fields are in phase...
Imagine a long deformable rod which has just been hammered on the top end (the bottom end is clamped to Earth). Consider a time interval $dt = t_{2} - t_{1}$ in which the pressure wave is traveling somewhere within the length of the rod (meaning some portion of the object has already "felt" the...
I'm quite aware that according to Einstein light is a particle and a wave at the same time.
However, I try to imagine how exactly would light expand. A photon must likely have a certain timing for expansion. I mean, after a photon is originated it immedialy multiplies itself into many other...
Hi,
This is a simple question that I just wanted to clarify. I was reading the following paper on label propagation: HERE and I can't understand whether the terms are vectors or scalars in one of the equations - specifically, equation (2.15) shown in the image below.
My understanding:
- ##f##...
I have an answer to a partial differential equation.
I have the equation coded as followed. I am trying to get this wave to propagate back after it hits a given z value. Can anyone help me figure out the direction in this equation...
I have seen that there are two different formulas that we can use when calculating the propagation of uncertainty in a measurement. If ##X=f(A, B, C, \ldots)## is the quantity whose uncertainty we want to estimate, which depends on the quantities ##A,B,C,...##, then we could calculate the...
In the book "Fundamentals of photonics", the authors defined waveguide modes using the notion of linear systems, where they said:
"Every linear system is characterized by special inputs that are invariant to the system, i.e., inputs that are not altered (except for a multiplicative constant)...
Assume that we have a 1.5 km x 100 cm^2 long straight pipe, totally inelastic and full of water. From time t = 0, a pressure of 300 000 Pa is continuously applied to the water with a piston at one extremity. This correspond to a force of 30 000 N on the pipe cross section in the direction of the...
Hi,
I have a value ##100 \pm 0.1## and a function ##\frac{V}{E} = \frac{1}{\sqrt{1 + (\omega r c)^2}}## and I would like to find the uncertainty.
Where r = 1000 and c = ##5 \cdot 10^{-8}## are constants.
However, I'm not sure to understand how.
Here's what I think and did.
Since I multiply the...
Do you have accessible web links discussing the pros and cons of the various theories of light propagation in dense media? I have done quire a bit of searching, but all seems rather superficial (Don Lincoln's video, f. ex.)
Thanks
Hello everyone, I would really appreciate some help on the following problem on plane waves and propagation. Not too sure if my attempt at writing the propagation wave expressions are correct, and how to handle the arbitrary function f(u). For the velocity, the wavelength is not specified, so is...
Hello,
Regarding the wave oblique angle propagation and based on Balanis "Advanced engineering Electromagnetic" book on page 136 ( it has been attached) I need to know why the phase velocity in x direction is not important to keep in step with a constant phase plane( Just equation 4-23).
I...
At 0:51 in this simulation video there seems to be a brief moment upon merging that these singularities produce what appears to be negative gravitational "Spike?" that seems to bulge spacetime in an opposite metric compared to normal spacetime flatness. Is this a quirk of the simulation or is...
I have an integral that depends on two parameters ##a\pm\delta a## and ##b\pm \delta b##. I am doing this integral numerically and no python function can calculate the integral with uncertainties.
So I have calculated the integral for each min, max values of a and b.
As a result I have obtained...
Hi, I need help finding the phase difference between the two rays converging at F'.
I was given this figure, the distance between the lenses is 10cm, the thickness of the lense is 1micrometer and the indexes are on the figure. The light is a laser in which lamda = 500nm.
I tried to write down...
Suppose you have a battery wired to a light bulb and switch via a long pair of conductors, say 1 light second long. Assume for now that electricity travels at c.
The switch is thrown. How long does it take the bulb to light? Does the electricity take 1 second to get from the battery to the...
So i understand completely what the first source is saying i.e. the longer the relaxation time, the more absorption of the ultrasound beam. The first paragraph of the second source however says the opposite- "very long" relaxation times mean the sound wave passage is unaffected?
My attempt at a...
An example (I think) of creating a phenomena that appears to propagate faster than the speed of light would be to have a line of people holding flashlights and giving each person a schedule of when to blink his light. With proper schedule we could create the illusion that point of light is...
I saw the solution of the light propagates in cylinder.. so in every solution there is the first order Gaussain function (the slandered one) times another function which gives I think the separation, both of them gives the intensity separation.. So what does that mean?! is it as I draw on the...
I read articles talk about the absorption of the exciton in a solvent, such as TIPS Pentracene in toluene. My question is does the absorption spectrum keep the same for aggregate TIPS Pentracene , in case if I want to know for a layer of TIPS Pentracene?!
My second question is: let's say I know...
Summary:: A plane wave incident upon a planar surface - determining polarization, angle of incidence etc.
𝐄̃i = 𝐲̂20𝑒−𝑗(3𝑥+4𝑧) [V. m−1 ]
is incident upon the planar surface of a dielectric material, with εr = 4, occupying the halfspace z ≥ 0.
a) What is the polarisation of the incident wave...
The problem I am having is "What can you conclude about wave prorogation in SR given the results?". The best I can come up with is that the number of wave planes N crossing a section of spacetime in either frame is the same. The section may be bigger or smaller depending on which frame you're in...
Hey, after doing some reading I stumbled across a few fundamental questions.1) Do all EM waves across the EM spectrum , if they travel through space have their E field and B field amplitudes exactly equal and in phase and shifted 90 degrees from one another?
If the answer is yes then...
2) In...
Without assuming a universal speed that is constant in all inertial reference frames, is it a necessary consequence of Galilean symmetry that interactions are instantaneous? If this is the case how can we prove this?
For a lab, I needed to calculate the uncertainty of a refractive index that was found using Snell's law. I found an equation online for propagation of error for any general function, which was
I thought that since my equation was
I could just get rid of the variable y, and have
After...
Hello!
In Optical fibers, let ##k_1## and ##k_2## be respectively the propagation constants in core and cladding, ##\beta## the propagation costant of a mode along the direction ##z##, ##a## the radius of the fiber. Using the normalized quantities ##u=a \sqrt{k_1^2 − \beta^2}## and ##w=a...
I am not sure what is meant by "equation of propagation of crest" but this is my attempt:
First, I find the velocity of wave:
v = ω / k = 0.5 / 0.25 = 2 m/s
Then I calculate wavelength:
k = 2π / λ
λ = 4 m
I imagine the crests will move to the right along with the wave so I try to use equation...
By reversibility, if we turn the direction of the light propagation by 180 degrees, then the new propagation path follows the old propagation path. I suspect that when there is diffraction, the light propagation is not reversible?
Moderator's note: This thread is a spin-off of
https://www.physicsforums.com/threads/what-are-the-most-important-open-questions-in-classical-physics.983671/
R. de Sangro, G. Finocchiaro, P. Patteri, M. Piccolo, G. Pizzella, "Measuring propagation speed of Coulomb fields", Eur. Phys. J. C 75...
I am uncertain if this belongs in the differential geometry thread because I don't know what area of mathematics my question belongs into begin with, but of the math threads on physics forums, this one seems like the most likely to be relevant.
I recently watched a video by PBS infinite series...
Hi!
I was wondering how would I calculate the uncertainty of a value that is calculated using both multiplication and division?
For example, with something like:
Q = mc(T2 - T1)
I'm not sure what to do with the uncertainties for T2 - T1
uncertainty = Δm/m + Δc/c + (ΔT1 + ΔT2)/(T1 + T2)
Or...
In a step-index optical fiber, considering Bessel functions of order ##\nu = 0## and no ##\phi## dependence, it is possible to obtain two separate sets of components, which generate respectively TE and TM modes. In the former case, only ##E_{\phi}##, ##H_r##, ##H_z## are involved; in the latter...
The equation we used in this lab was Δλ = (λ^2 / 2Δd) where Δλ is the separation of the sodium D doublet lines and is the value we're trying to calculate, λ^2 is the wavelength of sodium light given in the lab manual (589 nm) and Δd is the distance one of the mirror moves to go from one faint...
Homework Statement: There are the propagation delays from High to Low and from Low to High, and I wonder if they are equal?
Homework Equations: That is
$$ t_{PLH}=t_{PHL}$$
I suppose they should be equal.