Minimal distortion in transmission line
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In all circumstances of signal the characteristic impedance for a transmission line is: -

\$Z_0 = \sqrt{\dfrac{R + j\omega L}{G + j\omega C}}\$

At low frequencies (below 100 kHz) where R and C dominate characteristic impedance is: -

\$\sqrt{\dfrac{R}{j\omega C}}\$ and this basically means the input impedance is X\$\angle -45\$

In other words at low frequencies you cannot terminate with a simple resistor but need a complex impedance. At high frequencies it becomes \$\sqrt{\frac{L}{C}}\$ which is a resistor.