If you’ve ever tried to simulate a circuit using nothing but paper and pencil, or tried to match your antenna to 50 ohms by making an educated guess, you’ve probably found yourself looking for some of these tools. Everyone has their favorite tools. Here’s my list!
Impedance Matching
Just a handy, free calculator when you don’t want to do the math. When I wanted to match to my mag loop to 50 ohms with a capacitor instead of small loop, this is what I used.
https://www.will-kelsey.com/smith_chart/
A really easy-to-use Smith Chart matching tool.
Circuit Simulation
https://www.analog.com/en/design-center/design-tools-and-calculators/ltspice-simulator.html
This software is surprisingly powerful and feature-packed, whether I’m simulating antennas, filters, or amplifiers. A lot of modern MOSFET manufacturers have models specifically for LT Spice so you can simulate the latest and greatest parts with very little effort. You can even use their “transmission lines” for simulating distributed element filters!
Antenna Modeling
Even though I am nowhere near proficient with this tool, it definitely belongs on this list.
Transmission Lines
https://wcalc.sourceforge.net/cgi-wcalc.html
Mostly for PCBs, but useful elsewhere as well.
Filter Design
http://www.ke5fx.com/aadeflt.htm
The elliptical low pass filters are especially useful when dealing with harmonics.
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