Transmission Line Calculator

Download your free PDF copy of the Smith chart by clicking here!

The Smith chart (PDF) might be a great visual aid providing a lot of insight, but unless you are designing a single or double stub matching network, it really is an overkill in this day and age of computer proliferation. The Smith chart might be compared with what a slide rule is to a calculator: quite a number people do not how to use the former. The younger among us might even not know what a slide rule is! Anyhow, young and old will enjoy below transmission line calculator, written by Kevin Schmidt, W9CF. Its use is quite straight forward. For the nostalic ones among us and also for reference, download your free PDF copy of the Smith chart here.

The bottom part of the applet is a plot. The x axis is the position along the line; x=0 is the input. You can zoom in on a portion of the plot by holding down the left mouse button on that portion and move down and to the right to highlight the region with a little square. You can do this multiple times too. If you hold down the left mouse button and move up and to the left, you can unzoom. The easiest way to get back to the original is to click calculate again.

Two user defined cable types are provided. For user 1, you enter the resistive part of the characteristic impedance, the velocity factor and the attenuation in dB/100ft at some frequency. If you want to extrapolate to other frequencies, the exponent would be exactly 0.5 if the loss mechanism were purely conductor losses, and that should be good enough for a first guess. Otherwise, the loss at a new frequency will be the ratio of the new frequency to this frequency raised to the exponent power times this attenuation. The reactive part of the characteristic impedance is calculated assuming only conductor losses.

User 2 does not scale the results with frequency. Instead you input the characteristic impedance both resistive and reactive parts, the attenuation and the velocity factor. These characteristics are assumed to not change with frequency.

For more detailed information, please refer to W9CF's page.

More Transmission Line and Smith Chart Utilities

AC6LA's Utilities

Check out the TL utility programs of Dan Maguire, AC6LA.