AM radios, the simplest version of modern radio transmission, is based on concepts from the 1890s which have seen more fine tuning than actual change. Here is a brief rundown of the parts of an AM radio, and how they make it function.
Here is your AM radio receiver shopping list: a two-terminal diode, two lengths of wire (both about ten meters long), a metal pole or stake, a crystal earphone, and a tuner. To make all these parts work together to receive AM radio signals, you need to get up close to a transmission tower, secure the stake or rod in the ground, run one of the lines of wire to another metal object, attach one end of the diode to the end of this wire, and attach the other wire to the other end of the diode and to the tuner. Then, simply tune the radio transmission to receive the radio signal and pop the crystal ear piece in. You should hear everything just fine!
So, now you know how to create your own makeshift AM radio transmitter, which might just save you during a zombie apocalypse. However, it doesn’t do much to explain how the science behind it works. Here is the brief rundown of those details.
When a radio tower transmits radio waves, they are sent out at various electromagnetic frequencies. By either being close to a major signal or using a tuner you can determine which frequency you’re receiving. The diode you’re using detects the AM signals being shot out over the airwaves, and the electrical current being sent out is channeled through the antenna. The channeled signal sends reverberations which are being picked up by your crystal ear piece.
In the case of actual radios, we have two major additional pieces: the amplifier and improved antennas. The amplifier will take these sonic reverberations and magnify them dramatically in order to create the level of sound that we are used to in our modern systems. The improved antenna picks up signals more clearly and from further away. Otherwise, the concept is identical!