SU605343A1 - Method of transmission of two black-and-white tv programs - Google Patents

Description

one

The invention relates to television.

A device for generating a color synchronization signal in a SECAM system decoder is known, which contains a control unit, to the counting input of which line-down reverse pulses are delivered, a frequency detector, to the second input — which is a chrominance signal, and to the control input — C-typing horizontal clock pulses, integ | rator 1.

However, in the known device low noise immunity.

The purpose of the invention is to improve noise immunity.

To do this, a color synchronization device in the SECAM decoder, containing a control unit, on the counting input of which a pulse sweep is applied, a frequency detector, on the second input of which a chrominance signal is fed, and on the control input - a gate horizontal sync pulse, the integrator, between the output of the frequency detector and the input of the integrator, the entered normally closed key is switched on, and between the output of the integrator and the input of the control unit, the entered normally open key is switched on h, and to the control inputs of the key-boih filed retrace pulses frame scanning.

The drawing shows the structural scheme of the proposed device.

Color synchronization signal shaping device In the SECAM decoder, it contains a control block 1, the counting input of which is fed backward pulses, a frequency detector 2, the second input of which has a chrominance signal, and the control input is a strobing horizontal sync pulse, integrator 3, between the output of the frequency detector 2 and the input of the integrator 3, the entered normally closed key 4 is switched on, and between the output of the integrator 3 and the input of the control unit 1, the entered normally open key 5 is switched on, with than the control inputs of both keys 4 and 5 are fed by reverse frame pulse. The device works as follows.

At the start of the forward stroke across the field, the normally closed key 4 closes. When receiving a color program from the output of frequency detector 2, the integrator 3 receives impulses formed by packet detection

unmodulated subcarriers are reversed in rows. Since the frequencies of these packets are different in the adjacent rows, the pulses contain a component of a half-line frequency. Integrator 3 will highlight this component.

The higher the quality factor of the integrator 3, the

the greater its noise immunity, but the longer the oscillations increase at its output. With the Q of the Integrator, the process of establishing the oscillations will end approximately

zo

through periods, i.e. 200 lines.

7G

At the end of the forward stroke across the field, the normally closed key 4 is opened, and the normally open key 5 is closed. After that, the integrator 3 is disconnected from the frequency detector 2 and connected to the control unit 1. Due to this, the interference present in the signal on the return path across the field (as there are no subcarrier packets in the signal, the noise on the return paths through the lines freely penetrate the frequency detector 2) does not affect the integrator 3, which continues to maintain oscillations at its output with a phase determined by the switching phase on the transmission side. These slowly damped oscillations come through a normally open key 5 to the correction input of the control unit 1. With the correct phase of this device, the signal from integrator 3 does not affect it, and if it is incorrect, it makes corrections. At the beginning of the next forward stroke, the normally closed key 4 is closed, and the normally open key 5 is opened. A new energy storage cycle in the integrator 3 begins. For the time of this cycle, the control unit 1 is driven by pulses from a horizontal scanning unit. Therefore, the disappearance of individual pulses and even

The range of identification pulse does not affect the operation of the proposed device.

In the proposed device, the violation of color synchronization is excluded, since the integrator 3 is disconnected from the frequency detector for the time of the return stroke across the field.

Thus, in the inventive device, the color burst noise immunity is significantly increased.

Claims (1)

1. USSR author's certificate No. 279496, cl. P 04N 9/46, 1970.