RF modulator
An HF modulator or TV modulator ( RF modulator ) is used in video technology to modulate a television signal onto a high- frequency carrier frequency (hence the letters HF for high frequency or RF for radio frequency ) .
A practical application is, for example, the connection of home computers or video devices (e.g. DVD players ) to older televisions without a SCART socket via the antenna input . As a rule, the frequency range between channel 30 and 40 is used for this.
In older video recorders or satellite receivers there are almost always simple modulators in order to receive the video signal in addition to the antenna signal that is looped through at the antenna output of the device. With the extinction of televisions without video inputs, these have often been saved since the 2000s. An external HF modulator is essential for connecting a television without composite connections ( Cinch or SCART socket) to a video source without a built-in HF modulator. Also for feeding in a video signal, e.g. B. from a surveillance camera , a modulator is required in the house distribution.
In the case of simple devices, the channel is usually set within a range of around ten channels using a trimming capacitor . With better devices, the channel is set using a phase-locked loop (PLL circuit) and can be shown on a display (with stand-alone devices; e.g. an LED display ) or an on-screen display (OSD menu) become. Simple devices often produce interference in adjacent channels, so that integration into an existing antenna or cable system is problematic. With correspondingly more complex devices, this is prevented by filter circuits .