In a national transmission system, the characteristic impedances of the 4-wire circuit and the 2-wire circuit are 1200 ? and 1000 ? respectively. The average phase velocity of the signal in the circuit is 3 × 10⁷ m/s. If the largest distance of a connection is 300 km, determine the return loss and round trip delay for echo.

RL = 20 log (Z₄ + Z₂)/( Z₄ - Z₂) DB

Here RL = return loss

Z₄ = impedance of the 4-wire circuit

Z₂= impedance of the 2-wire circuit

RL = 20 log(2200/200) = 20.8 DB

Round trip delay for echo = (300 X 10₃)/( 3 x 10₇) = 10 ms.