# Signal Wavelength vs Transmission Line Length

1. ## 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"? •

2. ## 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. •

3. ## Re: Signal Wavelength vs Transmission Line Length

Hi,

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

4. ## 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. 5. ## 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. --[[ ]]--