Tuner (radio)

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A tuner is an adjustable device which passes one radio frequency, or band of frequencies, and excludes others, by using electrical resonance. A tuner performs the process of selecting the desired signal but its output is not directly usable and must be sent to another device. Typically tuners are sold with built-in audio amplifiers, loudspeakers, and/or a video display to form a radio receiver or television set. Tuners can be either stereo or mono, and are available for TV, FM, AM, and other types of radio signals.

A radio tuner receives radio broadcasts and converts them into audio-frequency signals which can be fed into an amplifier driving a loudspeaker. FM tuner, AM tuner, DAB tuner, etc. are types of radio tuner dealing with transmissions using different methods of modulation. The term tuner is used both for part 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 simplest tuner consists of an inductor and capacitor 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. Combined with a detector, also known as a demodulator, it becomes the simplest radio receiver, often called a crystal set.

Standalone audio stereo FM tuners are sought after for audiophile and TV/FM DX applications, especially those produced in the 1970s and early 1980s, when performance and manufacturing standards were among the highest. In many instances the tuner may be modified to improve performance. A growing hobby trend is the electronics specialists that buy, collect and restore these vintage FM or AM/FM audio tuners. The restoration usually begins with replacing the electrolytics (capacitors) that age over time. The tuner is outfitted with improved tolerance and better sounding upgraded parts. Prices have increased relative to the increasing demand for the older audio tuners. Those with the most value are the best sounding, most rare (collectible), the best DX capable(Distance Reception)and the known build quality of the component, as it left the factory.^[1]

Most of the top end audio tuner models were designed and manufactured to receive only the FM broadcast band. As FM became more popular, the limitations of AM became more apparent, and the primary listening focus, especially for stereo and music broadcasting. The bulk of tuners made for the market, however, were AM/FM design, especially in the 1980's and 1990's. Few companies even manufacture dedicated FM or AM/FM tuners now, as these bands are most often included in a low cost chip for A/V systems, more as an afterthought, rather than designed for the critical FM listener. The FM aficionado must really look to the classic tuner models and either rebuild or upgrade the unit to satisfy demanding FM listeners. A few 1970s tuners feature now-deprecated Dolby noise reduction for FM broadcasts.

A television tuner converts an RF television transmission into audio and video signals which can be further processed to produce sound and a picture. Different tuners are used for different television standards such as PAL, NTSC, ATSC, SECAM, DVB-C, DVB-T, T-DMB, open cable. For example, as the United States switches off its NTSC analog television services in 2009, ATSC tuners will be used to convert existing analog receivers for over-the-air reception.

VHF/UHF TV tuners are rarely found as a separate component; however cable boxes serve as a separate tuner, and have channel 3/4 outputs so they can serve as a cable-ready emulator for TVs that aren't cable-ready, and often feature composite, S-video, or component video outputs so they can be used on video monitors that do not have a TV tuner, or ones whose tuner is not working. They are usually bundled with a monitor, VCR, and/or PVR. However, they do exist for use by members of the television industry, and may be purchased on Internet Auction Sites, such as eBay.

TV tuners are also installed on PCI computer expansion cards (or in USB device, or even as a part of video card), together with a DSP, allowing a personal computer to display and/or capture television channels. A number of earlier models were stand-alone tuners, designed to deliver TV picture through a VGA connector. This allowed viewing television on a computer display, but, of course, did not allow recording programs by the PC.

Audio Broadcasting Terminology AM is Amplitude Modulation FM is Frequency Modulation SW is Short Wave (modulation) MW is Medium Wave (modulation) Obsolete Television Broadcasting Terminology" VHF is Very High Frequencies (defunct February 17, 2009) UHF is Ultra High Frequencies (defunct February 17, 2009).

[edit] Transmitting tuner

Another type of radio tuner sometimes known as an antenna tuner allows a transmitter to be efficiently operated with antennas and transmission lines that are not matched in impedance. Such a tuner is useful when operating an antenna system over a wide range of frequencies.