# Sensing the characteristic impedance of the transmission line

#### kintaro

Joined Jun 1, 2022
16
I found that an easy way to get the information of a characteristic impedance of a transmission line is to use a voltage pulse.
As below, the pulse varies from 1V to 0.3V. When the pulse drops from 1V to 0.3V, the voltage at 'node' drops to 0.558V before going back to 1V.
Interestingly, the 0.558V happens to be the case if we consider the transmission line as a resistor of 60 Ohm.
Why is that for that short period this happens?

Does anyone know how to explain it conceptually?
Thanks.

#### nsaspook

Joined Aug 27, 2009
10,698

#### crutschow

Joined Mar 14, 2008
31,126
Why is that for that short period this happens?
It's the time it takes for the signal to transfer the length of the transmission line.

#### WesBrodsky

Joined Dec 27, 2019
13
I found that an easy way to get the information of a characteristic impedance of a transmission line is to use a voltage pulse.
As below, the pulse varies from 1V to 0.3V. When the pulse drops from 1V to 0.3V, the voltage at 'node' drops to 0.558V before going back to 1V.
Interestingly, the 0.558V happens to be the case if we consider the transmission line as a resistor of 60 Ohm.
Why is that for that short period this happens?

Does anyone know how to explain it conceptually?
Thanks.
View attachment 281827
I found that an easy way to get the information of a characteristic impedance of a transmission line is to use a voltage pulse.
As below, the pulse varies from 1V to 0.3V. When the pulse drops from 1V to 0.3V, the voltage at 'node' drops to 0.558V before going back to 1V.
Interestingly, the 0.558V happens to be the case if we consider the transmission line as a resistor of 60 Ohm.
Why is that for that short period this happens?

Does anyone know how to explain it conceptually?
Thanks.
View attachment 281827
You have created at Time Domain Reflectometer. Look it up