(Please go ahead and move this if it's in the wrong section.) I'm a science fiction writer doing research for my latest book and hoping someone can help. A technically competent character (far more competent than me with my long-ago high school physics) - let's call him Jake - needs to build a device that generates several EM pulses at a fairly specific frequency. I believe he needs to build a spark-gap transmitter, something I'd never heard of until I started googling today, but he's stuck on a low-tech world with renaissance-era technology. The materials available to Jake are metal, wires, magnets, tools, etc. but no electricity or batteries. I'm happy for him to make a battery (from a lemon, perhaps?). If this no doubt odd-looking device creates dramatic sparks and smoke, all the better. I'm not worried about the receiver end of things, as that's taken care of. Is this possible? Could you describe how to make it, what materials are needed, and what it would look like? The online instructions I've so far discovered either use materials Jake doesn't have, or create too complicated a device for Jake's purpose. Thanks in advance.