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taz
Joined: 29 Aug 2004
Posts: 4
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 31 Aug 2004 9:38 why waves can travel in both diretions in a transmition line |
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Hi ,
why radio waves can travel in both diretions in a transmition line ?
tnks
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brmadhukar
Joined: 21 Jun 2002
Posts: 844
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| 31 Aug 2004 10:03 Re: why waves can travel in both diretions in a transmition |
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Hi,
Because it is an isotropic medium. What prevents it from travelling on either directions.
B R M
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yjkwon57
Joined: 31 Jul 2004
Posts: 221
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| 31 Aug 2004 10:24 Re: why waves can travel in both diretions in a transmition |
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| 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.
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eirp
Joined: 11 Dec 2001
Posts: 807
Helped: 9
Location: Phase center
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| 31 Aug 2004 10:40 Re: why waves can travel in both diretions in a transmition |
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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)
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mhamed
Joined: 28 Jul 2004
Posts: 117
Helped: 8
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| 31 Aug 2004 10:42 why waves can travel in both diretions in a transmition line |
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| 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.
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koushikr_in
Joined: 18 Aug 2004
Posts: 32
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| 31 Aug 2004 14:08 Re: why waves can travel in both diretions in a transmition |
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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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Kevin Weddle
Joined: 10 Jul 2004
Posts: 101
Location: San Antonio, TX
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| 31 Aug 2004 14:41 Re: why waves can travel in both diretions in a transmition |
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| 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.
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flatulent
Joined: 19 Jul 2002
Posts: 4878
Helped: 295
Location: Middle Earth
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| 31 Aug 2004 16:13 Re: why waves can travel in both diretions in a transmition |
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| One way to get an emotional feel for this is to think of light waves. You can see through a window in both directions.
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ravibg
Joined: 10 May 2004
Posts: 21
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| 31 Aug 2004 17:28 Re: why waves can travel in both diretions in a transmition |
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| 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.
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savadi
Joined: 14 Sep 2004
Posts: 27
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| 24 Sep 2004 0:03 Re: why waves can travel in both diretions in a transmition |
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| 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.
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djalli
Joined: 10 Nov 2001
Posts: 887
Helped: 15
Location: 1600 Pennsylvania Avenue, Washington DC 20500
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| 24 Sep 2004 8:01 Re: why waves can travel in both diretions in a transmition |
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| brmadhukar wrote: |
Hi,
Because it is an isotropic medium. What prevents it from travelling on either directions.
B R M |
You can say the same thing even for anisotropic medium
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djalli
Joined: 10 Nov 2001
Posts: 887
Helped: 15
Location: 1600 Pennsylvania Avenue, Washington DC 20500
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| 24 Sep 2004 8:05 Re: why waves can travel in both diretions in a transmition |
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| Kevin Weddle wrote: |
| 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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