The role of internal voltage source resistance in pulsed operation
The voltage at node 1 during the pulse will be V_0 / 2 (assuming transmission line impedance = Rsource). The input to the transmission line will continue to behave like a resistor until any reflection from the far end of the line reaches the start of the line again. If the line is terminated with the characteristic impedance then there will be no reflection and the input will continue to look resistive indefinitely.