Television tuner

A television tuner converts a radio frequency analog television or digital 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, DVB-T2, ISDB, T-DMB, open cable. An example frequency range is 48.25 MHz - 855.25 MHz (E2-E69), with a tuning frequency step size of 31.25, 50 or 62.5 kHz. Modern solid-state internal TV-tuner modules typically weigh around 45 g. Before the use of solid-state frequency synthesizers, covering the broad range of TV signal frequencies with a single tuned circuit and sufficient precision was uneconomic. Television channel frequencies were non-contiguous, with many non-broadcast services interleaved between VHF channels 6 and 7 in North America, for example. Instead, TV tuners of the era incorporated multiple sets of tuned circuits for the main signal path and local oscillator circuit. These "turret" tuners mechanically switched the receiving circuits by rotating a knob to select the desired channel. Channels were presented in fixed sequence, with no means to skip channels unused in a particular area. When UHF TV broadcasting was made available, often two complete separate tuner stages were used, with separate tuning knobs for selection of VHF band and UHF band channels. To allow for a small amount of drift or misalignment of the tuner with the actual transmitted frequency, tuners of that era included a "fine tuning" knob to allow minor adjustment for best reception. The combination of high frequencies, multiple electrical contacts, and frequent changing of channels in the tuner made it a high maintenance part of the television receiver, as relatively small electrical or mechanical problems with the tuner would make the set unusable. Analog tuners can tune only analog signals. An ATSC tuner is a digital tuner that tunes digital signals only. Some digital tuners provide an analog bypass. VHF/UHF TV tuners are rarely found as a separate component, but are incorporated into television sets. Cable boxes and other set top boxes contain tuners for digital TV services, and send their output via SCART or other connector, or using an RF modulator (typically on channel 36 in Europe and channel 3/4 in North America) to TV receivers that do not natively support the services. They provide outputs via composite, S-video, or component video. Many can be used with video monitors that do not have a TV tuner or direct video input. They are often part of a VCR or digital video recorder (DVR, PVR). Many home computers in the 1970s and 1980s used an RF modulator to connect to a TV set. Personal computers may be fitted with expansion cards (typically with PCI or USB interface) providing a TV tuner and digital signal processor (DSP). They may be dedicated TV tuner cards, or incorporated into a video card. These cards allow a computer to display and capture television programs. Many earlier models were stand-alone tuners, designed only to deliver TV pictures through a VGA connector; this allowed viewing television on a computer display, but did not support recording television programs. Smartphone and tablets can use a Micro USB DVB-T receiver to watch DVB-T TV.