The
time varying electrical signal voltage obtained from the TV camera tube circuit
representing the special distribution of brightness information in the image is
called the picture signal or the video signal. The signal contains frequencies
that depend on the scanning speed and the variation in the brightness of the
image over the scanning lines. Because of the fast scanning rate used in
television systems, the signal changes very rapidly with respect to time and
hence contains a wide range of frequencies with bandwidth typically in the
range of 25Hz to 5MHz. The weak signal obtained from the camera pick-up tube is
amplified in video amplifiers which are RC-coupled amplifiers with extended
frequency response.
time varying electrical signal voltage obtained from the TV camera tube circuit
representing the special distribution of brightness information in the image is
called the picture signal or the video signal. The signal contains frequencies
that depend on the scanning speed and the variation in the brightness of the
image over the scanning lines. Because of the fast scanning rate used in
television systems, the signal changes very rapidly with respect to time and
hence contains a wide range of frequencies with bandwidth typically in the
range of 25Hz to 5MHz. The weak signal obtained from the camera pick-up tube is
amplified in video amplifiers which are RC-coupled amplifiers with extended
frequency response.
The
video signal must, in addition, contain synchronising pulses as signals that
identify the retrace or flyback of the scanning beam and can be used to control
the scanning rate at the receiver so that the scanning at the receiver and the
transmitter takes place in synchronism. The retrace should not be visible on
the receiver screen and is hence blanked by pulses that cut off the electron
beam in the picture tubes as well as the camera pick-up tube. The blanking and
sync pulses are thus inserted during the retrace period of the scanning to form
a composite video signal.
video signal must, in addition, contain synchronising pulses as signals that
identify the retrace or flyback of the scanning beam and can be used to control
the scanning rate at the receiver so that the scanning at the receiver and the
transmitter takes place in synchronism. The retrace should not be visible on
the receiver screen and is hence blanked by pulses that cut off the electron
beam in the picture tubes as well as the camera pick-up tube. The blanking and
sync pulses are thus inserted during the retrace period of the scanning to form
a composite video signal.
