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    Signal Wavelength vs Transmission Line Length

    I've read that a rule of thumb is:
    T-line length >= 0.1 Signal Wavelength

    you need to consider transmission line effects. But if the T-line is "shorter", T-line effects can be ignored.

    But regardless of length, if Zo =/= Zl wouldn't issues of reflection and impedance matching still apply?

    Why can T-line effects be ignored when it is "short"?

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    Re: Signal Wavelength vs Transmission Line Length

    It depends on order of mismatch. If you put 1000 Ohm 0.1λ it must be considered, because effect is very significant. For such huge mismatch effect vanishes around 0.001λ.



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    Re: Signal Wavelength vs Transmission Line Length

    Hi,

    Why can T-line effects be ignored when it is "short"?
    As already said:
    * the effects will be there

    But the effects on signal amplitude will be less and the effects in time will be shorter. Thus it's more likely they will not harm.

    Klaus
    Please don´t contact me via PM, because there is no time to respond to them. No friend requests. Thank you.



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    Re: Signal Wavelength vs Transmission Line Length

    The 1/10 lambda rules means, you can analyze transmission lines as lumped circuit (series L, shunt C) below this length without causing large errors. But the lumped elements must be still considered, their effect can be very small or large, depending on the impedance relations.

    If you are in an impedance matched design, it may be easier to use transmission line calculation methods even for short lines.



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    Re: Signal Wavelength vs Transmission Line Length

    A load Zl is seen different when it is looked through a tl. There is a famous formula saying zin= zo*(zload+jz0*tan(teta))...
    As you can observe, if teta is small enough(the line short enough), zin becomes zload. When the line length increases, the load start to be seen different.



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