What you’re doing in this process is exciting electrons on the transmitter side, the battery and coin, which excited electrons traveling through the air, which then is received as a signal on the receiving side and turned back into audio output. What you’re doing is completing a circuit between the battery terminals which creates an electromagnetic force which can be detected by the receiver in the AM radio.
In order to understand radios in more detail than what we’ve just discussed, we need to take a little trip through history.
Back in the early days of radio technology, in the whereabouts of the early 1900s, radio transmitters were referred to as spark coils. This was due to the fact that they created large high voltage sparks, upwards of 20KV, to send out a signal. The issue was, the message was sent out on all frequencies in the radio spectrum, meaning that there was essentially only one localized channel. This was all fine and dandy back in the days where no one was really using radio, but nowadays, do something like this and you’ll get fined or sent to prison.
These early spark coils were essentially doing the same thing as the coin and battery experiment except at a much larger scale, meaning that they had a lot higher range.
Riding the magic school bus back to the modern era, and today’s radios use sine waves to transmit all sorts of information, from audio to video to raw data. By utilizing sine waves for transmission, radios and devices can distinguish different channels based on frequency or the number of cycles per second. This allows tens to hundreds to thousands of channels on modern radios all in the same space without too much interference.
Every single radio has 2 parts: A transmitter and a receiver.
The transmitter is responsible for taking a string of data and encoding it into a sine wave. After that encoding happens, it can also be amplified, and then it is sent out across the air. The receiver, rather expectedly, receives the radio waves and decodes the message encoded into the sine wave. Each side of this system uses antennas to radiate and/or receive the signal.
Relating radios back to your life a little bit, chances are you’re reading this article as a result of a transmission of radio waves. Cell phones are radios in their most basic forms. They contain both transmitters and receivers and can run both at the same time. In general, phones use frequency modulation, or FM, in a frequency range of 800 MHz, in any one of over 1600 individual frequencies. All that data probably is meaningless to you right now, but hang onto it as we dive deeper.
The problem though, as you might have picked up, is that sine waves don’t natively carry any information. They provide a foundation for transmitting information. Like the oreo cookie is the transmitter for that delicious filling, or like crackers are the foundations to that dry aged gouda. You get the point.
In order to get sine waves to actually carry information, you need to modulate it to carry information. You can do this in 3 ways, pulse modulation, amplitude modulation, and frequency modulation.
Pulse modulation means that you turn the sine wave on and off, just like the IT guy suggested. Doing this allows you to easily send morse code, but that’s just about it. Pulse modulation is rarely used except to control clocks across the US. The simplicity of pulse modulation also allows one pulse modulator to cover massive areas, like the entire US.
Amplitude modulation, on the other hand, is what is utilized by AM radio stations and TV signals to encode data. In this format, the amplitude, or peak to peak voltage, of the wave is changed. You can imagine this as the wave from a person’s voice being combined with a sin wave to create a new rather complex sine wave with the same frequency, but with a lot more data inside.
Bringing all of these different techniques back into the real world, we can begin to understand them a little further. If you sit in your car and tune your radio to AM 680. That means that the transmitting station was operating at 680,000 Hz, meaning that the sine wave repeats 680K times per second. The voice of the speaker or the music is then modulated onto that wave through amplitude modulation. The signal is amplified up to 50,000 watts for larger AM stations and then sent into space utilizing the antenna.
Your car’s radio picks up that signal utilizing its own antenna. This can be as simple as a wire or metal stick. In conjunction with the tuner on your radio tuning to the specific frequency, the tuner starts resonating at the 680Khz signal. Called resonance, this principle allows the radio to essentially ignore any other signals in the air. The signal then passes to the detector or demodulator that takes the voice or music from the wave utilizing a device called a diode and translates it back into audio. The final step in the process is for the radio to amplify the signal so you can hear it and change the volume as needed.
FM Radios have different detector setups that translate frequency into sound rather than amplitude, but otherwise, operate in the same way.
Summarizing all of this theory, radios are simple devices that transmit data through exciting electrons that flow through the air. Data can be encoded onto a constantly changing signal utilizing different modulation techniques that have advantages and disadvantages to each method. Nearly everything that communicates wirelessly around us uses radio waves to do so, and creating your own simple radio is actually a very manageable task. Over the last century, radio has radically changed the course of humanity and rapidly accelerated the growth of the information age.