LTSpice ham radio simulation is a great way to learn more electronics and design useful projects. Why have I waited so long to use it?

Back in the 1980’s, a friend gave me a cracked copy of Micro-Cap, a SPICE simulator implemented in MS-DOS. I used it to explore some RF amplifier designs at the time, then moved on to other things – like life! Now that I am retired, I thought it might be fun and useful to explore more modern SPICE software.

In short, SPICE is an approach to simulating the performance of electronic circuits, particularly analog. It’s been around since the 1970’s as an open source simulation engine. You will discover that many firms have built commercial versions and extensions on top of the SPICE engine. LTSpice from Analog Devices (and its subsidiary Linear Technology) is probably the most popular free implementation.

SPICE is essentially a “virtual” breadboard. You enter an electronic circuit as a schematic, which then gets converted to a network list of devices and performance equations. These equations get solved during the simulation. You are presented with the results, typically as a graphic.

LTSpice comes with a library of many popular electronic components. You drop the symbols into a schematic and wire the devices together. Each symbol, say a capacitor or transistor, has an associated model which describes how it works.

In the picture above, you can see the results of my small signal equation of a magnetic loop attached to an amplifier. More on this project later. The graphic shows output voltage and phase while simulating the circuit with three different load impedance values.

LTSpice Ham Radio Simulation – The Learning Curve

You will find lots of information about SPICE modeling on the web. The documentation for LTSpice is okay, enough to get you going. I would say if you understand some electronics basics, the learning curve is not too steep, probably shallower than GNURadio, for example.

For me, it started with an equivalent circuit for a magnetic loop antenna. Elapsed time between installing LTSpice and producing a working simulation of an active loop antenna was about 60 hours. And a lot of this time went into understanding how to do behavioral modeling using Laplace transfer functions to create frequency dependent resistance for loop radiation resistance and skin effect loss. That was hard, but the basics were straightforward.

So far, my efforts have focused on ac small signal simulation, but LTSpice does all sorts of analysis and works really fast.