Transmitter

For broader coverage of this topic, see Signal transmission. For the band, see The Transmitters.

In electronics and telecommunications, a radio transmitter or just transmitter is an electronic device that creates radio waves using an antenna to send a signal transmission to a radio receiver. The transmitter makes a special kind of electric current called radio frequency alternating current, which is sent to the antenna. This makes the antenna send out radio waves.

Transmitters are important parts of many things we use every day that talk to each other without wires, like radio and television broadcasting stations, cell phones, walkie-talkies, wireless computer networks, Bluetooth-enabled devices, garage door openers, and two-way radios in airplanes, ships, and space crafts. They are also used in radar and navigation helpers. We usually call them transmitters when they are used for talking or finding things, not for things like microwave ovens.

People often use the word “transmitter” to mean a broadcast transmitter, like one used for FM radio or television transmitter. This can include the transmitter itself, the antenna, and sometimes even the building where it is kept.

Description

A transmitter is a device that sends messages through the air using invisible waves called radio waves. It can be a small part inside another device or a separate piece of equipment. When combined with a receiver in one unit, it is called a transceiver.

Transmitters are used for things like talking on the radio, watching TV, or connecting computers on a network. They take signals such as sound from a microphone or pictures from a camera and change them into radio waves. These waves travel through the air and can be picked up by a receiver far away. The radio waves from the transmitter go to an antenna, which sends the energy out as radio waves. The antenna can be inside the device, like in a cell phone, or placed on top of a building for stronger signals.

Operation

Main article: Radio transmitter design

Radio waves are made when electric charges move fast. These waves are created by changing electric currents in a metal part called an antenna. When an alternating current flows through the antenna, it makes changing magnetic and electric fields. If the frequency is high enough, these fields spread out as radio waves.

A radio transmitter is an electronic circuit that changes power from a battery or outlet into a radio frequency alternating current. This current goes to the antenna, which sends it out as radio waves. The transmitter also adds information, like sound or pictures, to these waves. When these waves reach a radio receiver, they make small currents that the receiver uses to get the information.

Components

A real radio transmitter has several important parts:

• In strong transmitters, a power supply circuit changes input power to higher voltages needed for a strong output.
• An electronic oscillator makes the radio frequency signal, usually a steady sine wave called the carrier wave. In modern transmitters, a crystal oscillator uses a quartz crystal to keep the frequency exact.
• A modulator adds information to the carrier wave by changing some part of it. The information can be sound, pictures, or digital data. Different types of transmitters use different ways to add this information.
• A radio frequency amplifier makes the signal stronger so it can travel farther.
• An impedance matching circuit makes sure the transmitter and antenna work well together, so power is sent efficiently to the antenna.

In higher frequency transmitters, special designs are used to keep the frequency stable. Modern designs often use a phase-locked oscillator to keep the frequency accurate.

Regulation

When two radio transmitters send signals on the same frequency close together, they can mix up each other’s signals. This is important for things like emergency calls or airplane talks.

Most countries have rules about who can use radio transmitters and how. Governments give out licenses for different uses, like broadcasting or marine radio. They decide which frequencies and power levels each transmitter can use. An international group, the International Telecommunication Union, helps decide which parts of the radio spectrum each user can use. Some transmitters need a special call sign to show who they are.

Some small, low-power devices like cell phones, cordless phones, walkie-talkies, Wi‑Fi, and baby monitors can be used without a special license. But they still need to meet safety and quality rules before they can be sold.

History

Main article: History of radio

The first simple radio senders were made by a scientist named Heinrich Hertz in 1887. He used a spark to create radio waves. Soon after, Guglielmo Marconi used these senders to send messages, starting around 1895. Early senders could only send dots and dashes, using a special code called Morse code.

Later, new kinds of senders were invented, and by the 1920s, they could send actual sound. This started radio broadcasting. Over time, smaller senders were made, like those in walkie-talkies and cell phones, using tiny parts called transistors. Today, senders are very small and help us connect through Wi-Fi and cell networks.