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These use even larger antennas called ground dipoles, consisting of two ground connections 23–60 km (14–37 mi) apart, linked by overhead transmission lines to a power plant transmitter. AM – in AM, the amplitude of the radio carrier wave is varied by the audio signal. AM broadcasting, the oldest broadcasting technology, is allowed in the AM broadcast bands, between 148–283 kHz in the low frequency band for longwave broadcasts and between 526–1706 kHz in the medium frequency band for medium-wave broadcasts. Because waves in these bands travel as ground waves following the terrain, AM radio stations can be received beyond the horizon at hundreds of miles distance, but AM has lower fidelity than FM. Radiated power of AM stations in the US is usually limited to a maximum of 10 kW, although a few (clear-channel stations) are allowed to transmit at 50 kW.

Due to the small bandwidth, these systems cannot transmit voice, only text messages at a slow data rate. The communication channel is one-way, since the long antennas needed to transmit VLF or ELF waves cannot fit on a submarine. VLF transmitters use miles long wire antennas like umbrella antennas. A few nations use ELF transmitters operating around 80 Hz, which can communicate with submarines at lower depths.

So there is an incentive to employ technology to minimize the bandwidth used by radio services. The existence of radio waves was first proven by German physicist Heinrich Hertz on November 11, 1886. The first commercial radio broadcast was transmitted on November 2, 1920 when the live returns of the Harding-Cox presidential election were broadcast by Westinghouse Electric and Manufacturing Company in Pittsburgh, under the call sign KDKA. Canada when station XWA in Montreal began transmitting experimentally in September 1919 and on a regular schedule the next year. (The first commercially sponsored stations in Canada appeared in 1922.) The first British station offered two daily half-hour programs of talk and music from Chelmsford in 1919–20.

Many of these devices use the ISM bands, a series of frequency bands throughout the Radio spectrum reserved for unlicensed use. Although they can be operated without a license, like all radio equipment these devices generally must be type-approved before the sale. Internet radio or web radio can be used to describe a station that broadcasts via streaming over the web instead of using the conventional FM frequencies.

The transmitter emits a narrow beam of radio waves which is swept around the surrounding space. When the beam strikes a target object, radio waves are reflected back to the receiver. Since radio waves travel at a constant speed close to the speed of light, by measuring the brief time delay between the outgoing pulse and the received "echo", the range to the target can be calculated. The targets are often displayed graphically on a map display called a radar screen. Doppler radar can measure a moving object's velocity, by measuring the change in frequency of the return radio waves due to the Doppler effect. Digital Radio Mondiale is a competing digital terrestrial radio standard developed mainly by broadcasters as a higher spectral efficiency replacement for legacy AM and FM broadcasting.

But the transmission areas are limited in the radius around the transmitter. The receiving devices do not communicate back to the transmitter. For internet radio, an internet connection between the transmitter and the receiver, is actually necessary.

It transmits audio as a digital signal rather than an analog signal as AM and FM do. DAB has the potential to provide higher quality sound than FM , has greater immunity to radio noise and interference, makes better use of scarce radio spectrum bandwidth and provides advanced user features such as electronic program guides. Its disadvantage is that it is incompatible with previous radios so that a new DAB receiver must be purchased.

Electronic countermeasures – Military defensive electronic systems designed to degrade enemy radar effectiveness, or deceive it with false information, to prevent enemies from locating local forces. It often consists of powerful microwave transmitters that can mimic enemy radar signals to create false target indications on the enemy radar screens. Radio broadcasting means transmission of audio to radio receivers belonging to a public audience. FM broadcasting was introduced in the late 1930s with improved fidelity. Most radios can receive both AM and FM and are called AM/FM receivers. Two radio transmitters in the same area that attempt to transmit on the same frequency will interfere with each other, causing garbled reception, so neither transmission may be received clearly.

In order to receive the weak signals from distant spacecraft, satellite ground stations use large parabolic "dish" antennas up to 25 metres in diameter and extremely sensitive receivers. Portions of the UHF, L, C, S, ku and ka band are allocated for space communication. A radio link that transmits data from the Earth's surface to a spacecraft is called an uplink, while a link that transmits data from the spacecraft to the ground is called a downlink. Bluetooth – a very short-range wireless interface on a portable wireless device used as a substitute for a wire or cable connection, mainly to exchange files between portable devices and connect cellphones and music players with wireless headphones.