Radio Digital Tuner

A tuner is a circuit module or free-standing piece of equipment which locates radio frequency signals, even those of low amplitude and amplifies and converts them to a form suitable for further processing. A radio tuner receives radio broadcasts and converts them into audio-frequency signals which can then be fed into an amplifier driving a loudspeaker.
An audio frequency (abbreviation: AF), is periodic vibration whose frequency is able to be heard by the average human. While the range of frequencies that any individual can hear is largely related to environmental factors and differs greatly, the generally accepted standard range of audible frequencies is 20 to 20,000 hertz.
Frequencies below 20 Hz can usually be felt rather than heard and frequencies above 20,000 Hz can sometimes be sensed by young people, but high frequencies are the first to be affected by hearing loss due to age and/or prolonged exposure to very loud noises.

The word tuner is used both for parts of a radio receiver which also contains an amplifier section and for a boxed piece of equipment to be connected to a separate amplifier.
The simple tuner consists of a circuit in which an inductor and a capacitor are connected in parallel. The capacitor is usually made to be variable (although the inductor can made variable it requires a more complex mechanism and is rarely used). This creates a resonant circuit which responds to an alternating current of one frequency. In general, radio makers will use a rule of thumb of 1.5 picofarads per metre wavelength. Common inductance values are 4.1 milliHenries for long wave, 370 microHenries for medium, and 130 nanoHenries for VHF (FM) between 88 and 108 MHz. In a superheterodyne radio the capacitor that tunes the "tank" will be ganged with another; this alters the local oscillator to provide a constant intermediate frequency.

In the area of home audio systems, the term "receiver" often refers to a combination of a tuner, a preamplifier and a power amplifier, all on the same chassis. This is also referred to as an integrated receiver while a single chassis that implements only one of the three component functions is called a discrete component. Some audio purists still prefer three discreet units - tuner, preamplifier and power amplifier - but the integrated receiver has, for some years, been the mainstream choice for music listening.

Harman Kardon Company made the first integrated stereo receiver in 1958. It had undistinguished performance, but it represented a breakthrough to the "all in one" concept of a receiver, and rapidly improving designs gradually made the receiver the mainstay of the marketplace. Many radio receivers also include a loudspeaker.

AV receivers today are a common component in a high-fidelity or home-theatre system. The receiver is generally the nerve centre of a sophisticated home-theatre system providing selectable inputs for a number of different audio components that include: turntables, compact-disc players, recorders, tape decks and video components (DVD players, video-game systems and televisions).

As the appeal of vinyl discs lessened, most modern receivers do not include inputs for turntables, which have separate requirements of their own. All other common audio/visual components can use any of the identical line-level inputs on the receiver for playback, regardless of how they are marked (the "name" on each input is mostly for the convenience of the user.) For instance, a second CD player can be plugged into an "aux " input, and will work the same as it will in the "CD" input jacks.

Some receivers can also provide signal processors to give a more realistic illusion of listening in a concert hall. Digital audio S/PDIF and USB connections are also common today. The home theater receiver, in the vocabulary of consumer electronics, comprises both the 'radio receiver' and other functions, such as control, sound processing, and power amplification. The standalone radio receiver is usually known in consumer electronics as a tuner.