Transmitters; What’s the Deal?

Everything from your cell phone to your internet-of-things toaster uses a transmitter in order to broadcast signals and information from one place to another using only the air. Although the uses for this technology have become increasingly new age, the technology itself is based in the fundamental, century-old development of the radio. Radios have been around for a long time, but few people understand exactly how transmitters actually work. Here’s an article to help you brush up on your tech knowledge:

Transmitters work by utilizing basic rules of electromagnetism. For example, if you use a piece of wire to connect the two terminals of a battery, electricity will begin to flow from one end to the other. This flow of electricity will in turn create a magnetic field that surrounds the wire.

transmitter2Now say you take another wire and position it so that it is parallel to the battery’s wire and about 5 cm away from it. If you take a sensitive voltmeter and connect it to this second wire, you’re going to get a reading every time you connect and disconnect the battery’s wire from one of the battery’s terminal. This is an example of what scientists have consistently found; any changing magnetic field can induce an electric field in a conductor. It’s worth noting that it’s the change in magnetic field that causes electrons to flow in the second wire; they only flow at the moment of change.

How does this relate to transmitters? Well, if you want to create a radio transistor, it can be as simple a process as creating a rapidly changing electric current in a wire. You could consistently connect and disconnect a battery, but a much easier way about it would be to create an alternating current (which would alternate sinusoidally between say, 10 volts and -10 volts) using a capacitor and an inductor. These electronic components work together to make an oscillator responsible for the alternating current, and then a few transistors can work to amplify that sinusoidal wave into a more powerful electromagnetic signal. That signal can then be transmitted into the air by use of an antenna.

But how does that actually convey information to anyone? Sine waves carry information by being modulated in some way that encodes data. This can be done through pulse modification, which simply entails turning the sine wave itself on and off. Pulse modification is good for Morse code and utilized to send signals to radio-controlled clocks in the United States, but otherwise it’s a little known and relatively uncommon method of sending information.

transmitter3Amplitude modification (more commonly referred to as AM) allows radio stations to encode information by changing the amplitude of the sine wave i.e. it’s peak-to-peak voltage. That means that the sine wave produced by a person’s voice might be overlaid onto the transmitter’s sine wave in order to vary its amplitude and carry the information of said person’s speech.

Finally, there’s frequency modification or FM. Fm radio stations and a huge variety of other wireless technologies including cell phones use frequency modification to broadcast information because it’s largely immune to static. FM uses very slight variations in a sine wave’s frequency to convey information.