Flywheel synchronization
The flywheel synchronization is a process that in particular the middle of the 20th century to stabilize the horizontal position of the lines in television receivers will be used.
The flywheel synchronization is based on the filtering of the line frequency by an oscillating circuit (referred to as a flywheel). Because the resonant circuit, due to its inertia, detects errors that arise, for example, from a change in the mean brightness, the lines have a more stable position relative to one another. However, large errors lead to a transient process, which is manifested in older devices in particular by the fact that the position of the fields at the top of the image does not match. The cause is the half-line pulses (satellites and V-pulses) in the synchronous signal, which should be suppressed before the signal reaches the resonant circuit. For test purposes there is a test image in which the upper half of the image is white and the lower half is black.
The idea of flywheel synchronization is also the basis for generating the subcarrier for demodulating the quadrature-modulated color signal in the PAL and NTSC processes. The synchronization with regard to the phase position is also carried out here only by a burst pulse at the beginning of the line, that is to say at the line frequency.
A flywheel circuit, in this case with half the line frequency, is often used to maintain a stable switch from line to line in PAL.
Because the synchronism of the line switching with SECAM is only established at the beginning of the fields, a flywheel circuit is practically mandatory, which is either in the deflection circuit of the receiver or as an oscillating circuit with half the line frequency in the separate SECAM decoder (e.g. in studio systems).