- Welcome
- What is radio?
- How radio works
- Frequencies and Bands
- Common types of radio today
Welcome
The purpose of this guide is to provide a convenient, plain language starting point for those who are brand new to radio activities.
This content is scoped to typical radio hobbyists located in the United States. A number of these topics could apply to other locations as well. After all, the laws of physics are universal. However, man-made constructs, geography, and the atmospheric conditions of the moment, can significantly impact radio activities. And, countries have their own regulations governing radio use within their jurisdiction.
Throughout the text, key terms are rendered in italics, and linked to their corresponding definitions in the Glossary. Audio and video media is clearly marked, and opens in a new pop-up window. And most images can be enlarged to full resolution, simply by clicking on them.
This information is shared for educational purposes, as a service to the radio community and the general public.
What is radio?
Radio is a technology that allows the transmission and reception of audio signals (like music, speech, news, or data) wirelessly over long distances using electromagnetic waves called radio waves.
The word "radio" comes from radiation (of electromagnetic waves). However, its practical application is built on predecessor discoveries and innovations from the realms of electricity, electronics, material science, wired communications, and many others.
How Radio Works
At its most basic, successful radio activity consists of three events:
- The transmission of the radio signal,
- its travel from the point of origin to a point of reception, and
- its receipt.
A radio signal consists of an audio signal that rides on a carrier wave. We will examine this relationship in detail a bit later, but for now, envision a Pony Express rider (the audio signal) riding on a horse (the carrier wave). The rider is carrying the information, and the horse transports the information from the point of origin to the destination. This is a useful analogy to help visualize how a radio signal functions.
Electrical power is used to transmit the signal. It usually becomes weaker as it travels due to interference, scattering, and other considerations. By the time it reaches the receiver, it typically has weakened enough that electrical power must again be utilized to amplify the incoming signal enough to be heard.
(Electricity applied at the source, electricity traveling through the air, and electricity utilized at the receiving end. Keep this foundation concept in mind as we proceed.)
1. At the point of transmission:
- Sound is converted into an electrical signal using a microphone.
- This signal modulates (rides on) a high-frequency carrier wave (the radio wave).
- The modulated wave is amplified and sent out through an antenna.
2. Travel:
- In its purest theoretical (and physically impossible to achieve) state, radio waves are emitted from a single perfect point and travel equally in all directions at the speed of light.
- However, in the real world, radio waves are affected by tangible things and electrical phenomena that cannot be avoided. Antennas are imperfect; even the most finely-crafted antennas impart a heightened focus in some directions, while inhibiting effectiveness in others. Radio waves must pass through, or are partially reflected or blocked by, walls and buildings. They can even reflect off certain levels of the atmosphere and carom around the Earth bouncing from sky to ground and back, with the distance reached being dependent on a host of variables such as atmospheric conditions, the frequency of the radio wave, and the amount of power used to transmit it.
3. At the receiving end:
- The antenna of the receiving radio picks up the now-weakened radio waves.
- The receiving radio is tuned to the same frequency that the radio signal was transmitted on.
- The receiving radio demodulates (separates) the audio signal from the carrier wave.
- The weak incoming audio signal is amplified and sent to speakers, and you hear the sound.
Frequencies and Bands
- Frequency refers to the number of times a repeating event, such as a wave or cycle, occurs within a given unit of time.
- The electromagnetic spectrum is the full range of electromagnetic waves, ordered by frequency or wavelength, encompassing everything from radio waves and microwaves to infrared, visible light, ultraviolet, X-rays, and gamma rays. These waves are measured in Hertz (Hz).
- Hertz (Hz) is the standard unit of measurement for frequency, indicating how many cycles or repetitions of a wave or event occur per second. These numbers are used to organize the electromagnetic spectrum into segments with similar characteristics.
- Radio waves are one segment of the electromagnetic spectrum, with frequencies typically from 3 kHz to 300 GHz. This segment is further divided and organized into Bands.
- Bands are specific ranges of frequencies within the radio wave segment of the electromagnetic spectrum that are grouped and allocated for particular purposes, such as radio broadcasting, television, or wireless communication.
- Different frequency bands are used for different purposes:
- AM (Amplitude Modulation): 530–1700 kHz – longer range, lower audio quality.
- FM (Frequency Modulation): 88–108 MHz – shorter range, better sound quality, less static.
- Shortwave (HF): 3–30 MHz – can bounce off the ionosphere for global reach.
- Higher frequencies (VHF, UHF, microwave) are used for TV, mobile phones, Wi-Fi, satellite radio, etc.
Common Types of Radio Today
- Traditional broadcast radio (AM/FM)
- Digital radio (DAB, HD Radio)
- Internet radio (streaming)
- Satellite radio (SiriusXM)
- Amateur (ham) radio
- Two-way radio (walkie-talkies, police radios, CB radio)