DK164623B - Reception apparatus for reception of television transmissions transmitted by cable with a gate circuit - Google Patents

Abstract

The purpose of the gate circuit is to prevent reception of outside wireless communication services. Behind the intermediate frequency amplifier (3) is a pulse clipper (17) which delivers the line sync pulses each time to an input of a coincidence circuit (19) at one time direct and at another time delayed by a line period. The coincidence circuit delivers a signal to a constant power source (20), which charges a condensor (21) which is continually discharged by means of a second constant power source (22). The voltage arising in the condensor delivers the switching signal for the gate circuit.

Description

DK 164623B

in

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a receiver apparatus for receiving television transmitted by cables with a multiple socket for input and output signals in the form of a SCART socket for connecting peripherals, with a gate circuit for avoiding reception of strangers. radio services, where the gate circuit is positioned before the audio output in the SCART socket, as well as with an impulse separation step for filtering out the horizontal frequency synchronous pulses.

As is well known, at the frequencies of cable television, there are also 10 channels which are assigned to foreign radio services by wireless broadcasting, such as TV channels. police radio, etc.

It is known to make such radio services inaudible by the silence of the sound channel upon receipt of a broadcast signal which does not conform to the television norm. This is done in a known manner in that the sound channel is only switched on by ascertaining the coincidence of the received line synchronization pulses and the line frequency pulses produced by the receiving device. This prevents the foreign radio services from being audible (DE patent 25 13 344). This circuit operates reliably when a receiving device is arranged only 20 for HF receiving signals. However, there are devices which do not exclusively serve to receive RF signals. With a special input (SCART socket) on the television receiver it is possible to connect e.g. games, computer, video tuner, VCR, if FBAS signal over a switch can be connected to the 25 video and synchronization steps with phase comparison and coincidence. These peripherals constitute pseudo-television transmitters to which the silent circuitry responds, ie. in the presence of a signal from the connected device, the audio channel is switched on, even when the television receiver is tuned 30 to the frequency of a foreign radio service. Thus, e.g. over an output switch for the sound in the SCART socket, e.g. over a headphone, make the foreign radio service audible. However, this does not correspond to the regulations which say that the sound of such a radio service must in each case remain inaudible.

The object of the present invention is also, in the case of connecting peripheral devices, in a simple manner to comply with the above mentioned requirements. According to the invention this is achieved by designing the receiving apparatus as set forth in the characterizing part of claim 1.

The invention will then be further explained with reference 2

DK 164623 B

to the drawing, in which fig. 1 is a block diagram of one embodiment of the apparatus according to the invention; and FIG. 2 shows the part of the block diagram of FIG. 1, which serves to produce the silence control signal.

An RF signal received by an antenna 1 is fed to a tuner 2 and thence to an MF stage 3 from which the audio channel and video channel are determined. Over an audio MF step 4, the audio signal is passed over a gate circuit 5 to an outside conductor 6 in a socket strip 7 for connection e.g. of a headphone as well as to a switch in a switch 8, the second switch of which is connected to an input terminal 9, from which the audio signals can be switched to the sound stage 10 in the receiver.

From the MF stage 3, the video signal is passed to an outside conductor 11 and to a switch in a further switch 12, the other 15 of which is connected to an input terminal 13. The input and output terminals 9, 13 and 6,11 serve to connect the receiving apparatus with the peripherals. The switch 12 is connected to the video signal stages 14 and to the deflection of the electron beams in the image reproducing tube 15. The control signal for effecting the gate circuit 5 is taken out of the MF signal and processed in a step 16 to be described in more detail with reference to FIG. 2nd

The FBAS signal is coupled to a pulse separator 17. The output of this pulse separator is partly over a delay circuit 18 and 25 and partly directly connected to a coincidence circuit 19. The output of this coincidence circuit 19 engages a constant current source 20 which charges a capacitor 21 as long as the pulse frequency. is routed to the circuit. Only by a television signal is the coincidence circuit 19 activated, whereby the capacitor 21 can be charged. There is another constant current source 22 which continuously discharges the capacitor 21. At a suitable ratio between the currents of the two current sources 20 and 21, it can be obtained that upon receiving television signals, the discharge current I ^ is greater than the discharge current I ^. A connected threshold value switch 23 provides 35 unambiguous switching and thus a unique generation of the Mute signal.

The circuit of FIG. 2 is particularly suitable for construction in integrated circuit technology.

For the delay circuit 18, e.g. a 5 3 is used

DK 164623 B

PAL delay line. The delay circuit 18 may also consist of a digitally working shift register where the delay time can be switched.

10 15 20 25 30 35

Claims (4)

4 DK 164623 B Patent claims. 1. Receiver apparatus for receiving television transmitted by cables with a multiple socket for input and 5 output signals in the form of a SCART socket (7) for connecting peripherals, with a gate circuit (5) to avoid receiving foreign radio services, wherein the gate circuit is arranged before the audio output in the SCART socket, and with a pulse separating step (17) for filtering out the horizontal frequency 10 synchronization pulses, characterized in that the horizontal pulses derived from the pulse ski 11 step (17) a delay means (18) is provided to a first input of a coincidence stage (19) to whose second input the non-delayed horizontal frequency pulses are applied and the output of the 15 coincidence stage (19) engages a first constant current source (20) for charging a capacitor (21) and another constant current source (22) continuously discharging this capacitor (21) and being charged the current is greater than the discharge current and that the voltage arising on the capacitor (21) over a threshold value switch 20 (23) serves as a signal for opening the gate circuit (5). Receiver apparatus according to claim 1, characterized in that the delay means (18) consists of a PAL delay line with modulator and demodulator. Receiver apparatus according to claim 1, characterized in that the delay circuit (18) consists of a digital shift register. Receiver apparatus according to claim 1, characterized in that the delay time of the delay means (18) is changeable. 30 35