LTSpice For Radio Amateurs (and Others)

We don’t think [VK4FFAB] did himself a favor by calling his seven-part LTSpice tutorial LTSpice for Radio Amateurs. Sure, the posts do focus on radio frequency analysis, but these days lots of people are involved in radio work that aren’t necessarily hams.

Either way, if you are interested in simulating RF amplifiers and filters, you ought to check these posts out. Of course, the first few cover simple things like voltage dividers just to get your feet wet. The final part even covers a double-balanced mixer with some transformers, so there’s quite a range of material.

We like LTSpice. It is powerful, easy to use, runs with Linux (using WINE), and the price is right. Since it is popular, there are also plenty of examples and tutorials, including this one.

We were glad to see [VK4FFAB] tackle transformers as they aren’t very easy to work through without some examples. We also talked about the transformer problem in part three of our LTSpice tutorial. In fact, you might find our video helpful when working through the first two post from [VK4FFAB]. We’ve seen other radio projects use LTSpice, including a regenerative receiver. If installing LTSpice is too much of a commitment for you, you can also do simulations in your browser. The Falstad simulator isn’t as powerful, but it does have some pretty neat features of its own.

16 thoughts on “LTSpice For Radio Amateurs (and Others)

    1. I second QUCS it really is great for simple stuff like this. The only time it is worthwhile to use LTspice is when you are doing (as the name implies) you are using parts from linear to do switchmode power supply design, since they have specialized macromodels for their parts that reduce simulation time by orders of magnitude.

      1. LTSpice imports (unencrypted) SPICE models from other manufacturers fine. Plus Wurth, as well as others, supply LTSpice libraries for their parts. Wurth is especially handy as they supply ferrites, which often don’t actually have enough information in their datasheets to actually understand how the part will behave.

      1. LTspice’s spice engine is really very good (way better than the open source spice implementations out there) at simulating the transients that come up in switchmode power supply design. Even relatively simple designs (ex, simple integrator feedback onto a halfbridge feeding a buck converter) can have convergence issues with the classic spice algorithms. I don’t know what gEDA uses but the qucsator engine used in QUCS is terrible for transient simulations such as that, and while ngspice is better LTspice seems to be a good bit faster. But the real difference is in the macroblocks provided by linear, you can get a macroblock for most of their controller chips which implements the entire control circuit as a ‘black box’ that simulates very efficiently and lets you easily simulate even complicated circuit designs with a lot of parasitic components (ringing, etc) for thousands of cycles in seconds.

        But, for RF (and other small signal or simple linear circuits) QUCS really shines, since it was written from the ground up to be able to RF work. The only other tool I have used that I liked as much as QUCS was Agilent’s ADS (licenses starting at about $10k) in terms of ability to quickly do RF design work. The only thing I wish QUCS had was a better way to do optimizations. In ADS you could do multi-dimension sweeps in real time (drag sliders for component values, and see the result pane update immediately), and it had advanced algorithms for doing optimizations (click minimize S11 and NF, then it could tweak dozens of parameters and find a solution in seconds).

  1. I haven’t looked at Qucs in a long time. It wasn’t ready then. I find it interesting to see a bunch of comments about it, maybe it’s time to check it out again! I’m not sure what’s up with the all-caps. It’s Qucs on their website. It reminds me of when people write HAM radio! Oh well… not important.

    LTSpice awesome. Very easy to use. It reminds me of Electronics Workbench or Circuit Maker from the 90s. It really bugs me though that some tools are good for simulating and others are good for designing PCBs but there doesn’t seem to be much integration between them. I don’t want to make my schematics twice! I wonder if there is a good way to convert between LTSpice and KiCad yet. Or.. maybe Qucs and KiCad. That’s another thing I wanted for a long time but haven’t actually checked on for a while. I think I’m off to Google now!

    1. Altium Designer has a SPICE engine built in, and it’s pretty decent, but you miss all the LTspice black box components and efficiencies that jrfl mentioned above. I spent a while getting the models into most our library components in altium at work, and then barely used it.

    2. I will argue that it isn’t useful to convert schematics from a simulator to a schematic entry tool.

      They aren’t the same kind of schematics. A real schematic has connectors, LEDs, microcontrollers, decoupling caps, and most of all, part data like part numbers, etc. A simulation schematic generally has only one portion of a real PCB, but it also has sources, cables, external loads, and ideal function blocks. In a simulation, you often pull component values out of thin air, so you don’t bother with part numbers and footprints.

      In short, you don’t run a real PCB schematic on a simulator, and you don’t implement an LTSpice schematic in a PCB tool.

    1. You can also use jPCBSim for planar pcb filter simulation. It is a front-end for openEMS FDTD engine. Once you have the numerical simulation completed, you can import your the s-parameter files for your pcb/copper filter into your circuit simulator.

  2. I guess you have made it when your crap ends up on Hackaday HAHAHA. Anyway, do not know how you found my blog posts Al, but thanks for sharing, I hope some other noobs and electronics beginners find them useful. I am no expert, but I have lots of fun doing and learning along the way.


  3. What will happen to LTSpice now that Linear Technologies Corp. (LTC) has been swallowed-up by Analog Devices Incorporated (ADI)? In my many years as an EE, LTC,has been (reasonably) friendly to designer/developers at any level.

    Unfortunately that has NOT been the case with ADI in my experience (don’t get me started. Grrrr….).

    I thank LTC for making LTSpice freely available (albeit proprietary). As a result I use LTC components where it makes sense. Remember that risk has cost and modelling can reduce risk. (provided you are careful). Plus, there is a large community dedicated LTSpice users who support the product and enhance it in many ways.

    Please ADI – Respect what LTSpice is! You must understand that if you Harm LTSpice in any way, you will LOSE many EE’s as a preferred supplier. In-fact you should ENHANCE LTSpice to include the likes of ADI & Hittite product models (where it makes sense of-course).

    Keep LTSpice free ADI!

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