3
\$\begingroup\$

Is every wire a transmission line or a transmission line has a special manufacturing process? But why during analysis of normal electrical circuits we never consider parameters like characteric impedance, R,G,L,C etc and only considered resistors, inductors etc which are actually connected in circuit? Don't these parameters affect analysis of circuit or they are considered only in some particular cases? If so what conditions are there that need to be satisfied after which I need to consider effect of transmission line parameters?

\$\endgroup\$
4
\$\begingroup\$

Every wire is a transmission line when the frequency of the signal gets to the point where the physical size of the wire is comparable to the wavelength of the signal traveling down the line.

In normal circuit analysis, we make several assumption. First, we are using DC or low frequencies and we assume wires are perfect with no parasitics and no resistance to it. There are other assumptions such as no coupling between magnetic fields. I am talking about a first course in circuit analysis.

There is no hard and fast rule. Typically the rule of thumb is that if the wavelength of the signal is about 1/10th of the length of the wire, that you should consider it a transmission line.

In practice this really manifests itself in 300MHz+, but in some cases 100MHz can also require some attention.

\$\endgroup\$
  • \$\begingroup\$ So while considering different modulation schemes do we need to consider transmission line effect as well? \$\endgroup\$ – Enthusiast Sep 13 '13 at 16:05
  • \$\begingroup\$ This is a bit complicated. Modulation is just the way you change the signal parameters to convey information. Transmission line can affect the output (and modulation as such), but typically what you want is to have good matching to transmit all the power to the antenna and waste as little as possible. \$\endgroup\$ – Gustavo Litovsky Sep 13 '13 at 16:28

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.