SHTFPreparedness may collect a share of sales or other compensation from the links on this page.
Please be sure to like SHTF AND PREPPING CENTRAL on Facebook; this means you won’t miss any of our posts that can help you prepare you and your family for survival in an emergency or SHTF situation.
The earliest type of radio transmitter that humans have created are spark-gap transmitters. They were first used around 1888 and remained legal until the 1920s, when their use became greatly restricted.
World War II delayed their complete ban outside of emergency communications for a few years. Now the only way to use them legally is inside a faraday cage. They operate as jammers for the same reason they were banned: they take up a lot of the radio spectrum.
A spark gap transmitter is fairly simple. Send a high-voltage current through an air gap; when the resistance of the air breaks down, a spark will cross the gap.
When this happens, electromagnetic radiation is emitted. You can test this in your house fairly easily. Turn on some speakers so they are powered, but nothing is coming out of them.
Computer speakers that are on will work, as will a stereo set to CD or tape with no CD or tape playing. Flip your room lights on and off in rapid succession; you should hear a clicking from the speakers. The clicking is RF energy that is being picked up from the light switch.
