# Transmission Lines and Impedance Matching: what is considered electrically 'short'?

 Quote by satchmo05 Hey all, Between two devices, I will need to have a coaxial line (with SMA connections on either end) connecting them. The operating frequency of the signal I am propagating is approximately 125 MHz. With this said, the wavelength (assuming ideal) is 2.4 meters. First, assume the $\epsilon_r=4\;$ velocity is about half of speed of light which is 1.5EE8 m/s. At 125MHz, λ= 1.2m, what you have is free air velocity. I have heard from numerous sources that if electrically 'long,' it is greater than 0.25λ, which is any length larger than 0.6 meters. Any transmission line length smaller than 0.6 meters is considered "electrically short." The is not correct at all. A short to the source is only refer to an open end coax 0.25λ long from the source. Any length longer or shorter will not be a short anymore. My question is in regards to impedance matching: if my transmission line is "electrically short," do I need to worry about impedance matching? Obviously, everything would be happy if I matched at the load, but I'm interested to know if I can skip a step. My thought is that since I'm at such a high frequency, attenuation and loss effects will be near negligible. Thoughts? Thanks for your help! - Satchmo05