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why waves can travel in both diretions in a transmition line

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taz

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transmition line

Hi ,

why radio waves can travel in both diretions in a transmition line ?

tnks
 

Re: why waves can travel in both diretions in a transmition

Hi,
Because it is an isotropic medium. What prevents it from travelling on either directions.
B R M
 

Re: why waves can travel in both diretions in a transmition

When one transmission line is terminated by a radio wave source at one end and by a load impedence, although one changes the positions of the radio wave source and the load impedence, the wave traveling characteristics will be the same. Since the superposition principle can be applied, the waves can travel in both directions.
 

Re: why waves can travel in both diretions in a transmition

It comes out from describing of the transmission line by differential equation. The solution has the form of 2 exponentials, one for <-- and second for --> direction

U(z)~A*exp(+j*k*z)+B*exp(-j*k*z)
 

this is because of transmition line charectristics.if you write the equation of wave in a line (V an I is decompose to V+ which goes in +z an V- which goes in -z direction) you see that V- is not zero becuse of ohm relation between I and V in a line so the wave goes in 2 direction.
 

Re: why waves can travel in both diretions in a transmition

u can also view this phenomenon in terms of power flow. when the entire incident power is not absorbed by the load (due to mismatch) what happens to the remaining power?

the rem power has to be reflected . this causes reflected waves and the wave travels in opp direction
 
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    Nemidu

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Re: why waves can travel in both diretions in a transmition

Energy that is returned like when a capacitor is there is not a reflected wave. A reflected wave does not travel in both directions. A reflected wave is simply the property by which the length of a transmission line causes a DC offset along the line. The transmission line has capacitance and inductance to it, but the length is the third key to a reflected wave. When they say the signal is reflected back up the transmission line, they are talking about the energy that is returned. The reason they use the reflected wave as an example is because it is easier to see what happens to the signal. You can see that the voltage adds. But to say it is reflected is a little erroneous. It's just returned energy with a visual aid in determining what the voltage is doing.
 

Re: why waves can travel in both diretions in a transmition

One way to get an emotional feel for this is to think of light waves. You can see through a window in both directions.
 

Re: why waves can travel in both diretions in a transmition

This concept is called bouncing in High speed digital design.It happens in case of RF frequencies alone.As the frequency tends towards DC,bouncing effect totally stops.
 

Re: why waves can travel in both diretions in a transmition

If you have impedance mismatches in input or output (receiver or transmitter) some of wave can be reflected. you can study transmission lines in david cheng book.
 

Re: why waves can travel in both diretions in a transmition

Kevin Weddle said:
A reflected wave does not travel in both directions.

Wrong! A reflected wave will bounce from load to generator, and vice-versa all the times.

At load or generator will alkways meet with different impedances other then characteristic impedance of line it is traveling,

So it will travel back and forth until it dies by being absorbed or scattered. it will obey a certain geometrical series.
 

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