An Interactive Introduction to Fourier Transforms
Using a series of animations, the author of this page, Jez Swanson, shows how Fourier transforms work. One of the first animations shows how a square wave is made up of an infinite series of harmonically-related sine waves. A frame of this animation is shown at right.
One of the cool things about these animations is that you can control how many of the sine waves are included in the reconstruction of the square wave and see in real time how that affects the “squareness” of the wave.
Overall, this is a very nice introduction to the topic. There aren’t any examples of how the Fourier Transform is used in software-defined radio, but you can extrapolate from the examples that are given.
Toroid King adds impedance matching network calculator
W8DIZ, the “toroid king,” runs the website toroids.info, where you can find all kinds of information on how to use toroids, including the physical dimensions and usable frequency range for a wide variety of toroids . The latest tool to be added to this list is the impedance matching network calculator. All you need to do is to select the type of toroid that you wish to use, input a frequency, and the input and output impedances, and the calculator will calculate not only the inductance and capacitance required, but also the number of turns and length of wire needed to wind the toroidal inductor.
In the [email protected] message that Diz used to announce the calculator, two other online impedance matching network calculators were mentioned:
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