Pilot signal
A pilot signal is in the telecommunications signal (usually a single frequency ), which is transmitted from the outside and independently of the actual useful signal via a communication channel. It is for control, control, reference or monitoring purposes.
Stereo radio
If the FM stereo radio broadcasts a 19 kHz pilot tone is also sent to indicate that a stereo signal is present. This pilot signal is used to obtain the necessary information for demodulating the stereo sub-carrier at 38 kHz ( 19.2 kHz) of the frequency doubling, which is not sent. The stereo information itself is sent 23-53 kHz in the area. (see FM Stereo)
The pilot tone itself carries no information (except for the presence of the stereo signal as well as the key for the demodulation phase position of the carrier ), but a pilot tone can also be used for transmitting narrowband information such as by being slightly amplitude modulated.
If the receiver itself does not remove these pilot tone, some cassette recorder will provide a switch that allows to switch on a so-called MPX filter, which filters out these pilot tone.
Sound film
When sound film one by one in the film camera built-in or flanged to this pilot tone generator delivered the synchronization between separate image recordings and sound recordings used. Alternatively, one of a quartz Pilottongeber supplied pilot tone to be used if the camera is also controlled quartz. The sync cable between film camera and tape recorder this is not necessary.
Analog tape recorders as Nagra or Stellavox are still working with the pilot tone method.
With analog recording, the tape material is indeed transported with a fixed belt speed, but the tape material itself can stretch or shorten slightly.
However, to facilitate an absolute precision for playback at exactly the same speed as in the recording, the tape recorder, a pilot frequency of exactly 50 Hz is generated. This 50 - Hz tone is recorded along with the audio recording. This frequency is a kind of electronic perforation, about using a control playback regardless of belt slip (stretching / shrinking ) is possible.
In the classical pilot tone, however, the information recorded on a separate track 50 Hz signal with the help of a Pilottonverstärkers will be intensified so that the synchronous motor of Perfoläufers can be driven. This serves to dub the original sound recording from the " lace " (1/ 4 " tape) on Perfoband / magnetic film. In this method, the synchronization between movie recording and the sound recording without any control is automatically ensured., The recorded magnetic film can subsequently on a film cutting table synchronously created and edited the image.
Wireless Microphones
Wireless microphones transmit a pilot tone ( switchable pilot tone monitoring ), etc. following information to the recipient:
- Battery status control,
- MUTE switch on the transmitter,
These data, supplied by pilot tone data are evaluated in pilot tone decoder of the receiver and displayed on the screen of the receiver.
Baby Monitor
Baby monitors have a pilot tone to avoid interference from other radio- operated devices.
Some battery-powered receiver change into an energy saving mode if over a longer period at the transmitter noise is not included. The pilot tone of the transmitter signals the receiver further that the transmitting device is operational and is in range.