# Quarter wavelength confusion

Reading up on quarter wave transmission lines and I'm confused about the actual length of the line.

Is a quarter wavelength line equal to the length of the incident and reflected wave?

Or is it only equal to the length of the incident wave?

vk6kro
Reading up on quarter wave transmission lines and I'm confused about the actual length of the line.

Is a quarter wavelength line equal to the length of the incident and reflected wave?

Or is it only equal to the length of the incident wave?

The incident wave and the reflected wave will have the same frequency.

In the same medium, they will travel at the same speed, so they will have the same wavelength.

• davenn
davenn
Gold Member
2021 Award
The incident wave and the reflected wave will have the same frequency.

In the same medium, they will travel at the same speed, so they will have the same wavelength.

yup
so --- λ/4 ( in metres) = 300/freq(MHz) /4 x VF ( Velocity Factor) of the transmission line

eg
300/1296 = 0.23m (free space wavelength)
0.23/4 = 0.057 (free space λ/4 wavelength)
0.057 x 0.66 = 0.038m electrical λ/4

The 0.66 VF I used is just a common velocity factor of a number of coaxial cables ( there are many others)

Dave

Ok, now I understand that part (thanks btw)..But what about when people say the quarter wavelength transforms an open circuit to a short circuit and vise versa?

Can someone explain that?
What I don't understand, say you have an open circuit, a quarter wavelength transforms it into a short circuit....so does this mean the source only sees a short and maximum current flows through the entire circuit?

Averagesupernova