WO1992017984A1

WO1992017984A1 - Tv-signal transmission pay-tv-system

Info

Publication number: WO1992017984A1
Application number: PCT/SE1992/000148
Authority: WO
Inventors: Björn PERSSON; Tomas Svensson; Arne Karlsson
Original assignee: Factum Elektronik Sweden Ab
Priority date: 1991-04-04
Filing date: 1992-03-10
Publication date: 1992-10-15
Also published as: SE9100986D0; SE466727B; AU1347792A; SE9100986A

Abstract

The present invention relates to a TV-signal transmission pay-TV-system which includes a transmitter, a number of system-subscribed receivers (13), a number of non-subscribed receivers (16), and a signal transmission medium (6, 7, 8) which connects the transmitter with respective receivers, wherein the transmitter is provided with, or coacts with a signal scrambling device and respective system-subscribed receivers are provided with or preceded by a signal-unscrambling device (14), wherein the signal-scrambling device and the signal-unscrambling device (14) are mutually so adapted as to unscramble a scrambled TV-signal transmitted from the transmitter and thereby regenerate a signal in its correct form, so as to form picture-correct lines and pictures and possibly also sound, while non-system subscribed receivers (16) receive distorted lines, pictures and possibly also distorted sound from the scrambled TV-signal, and wherein line signals according to a first system (MAC) are transmitted via the signal transmission medium. The system includes a first means (44) which functions to inhibit a first selected part ('a') of the line signals according to a second system (PAL) and a second means (44) functions to enable a second selected part to be applied to the line signals according to the PAL-system with a signal structure that conforms to the first system, (MAC).

Description

TITLE OF INVENTION. TV-signal transmission pay-TV-system

TECHNICAL FIELP The present invention relates to a TV-signal transmis¬ sion system, and more particularly, but not exclusively, to the use of a pay-TV-system of the kind which com¬ prises a transmitter, a number of receivers which belong to the system, called subscribed receivers, and a number of receivers which do not belong to said system, called non-subscribed receivers, and a signal transmission medium which connects the transmitter with respective receivers.

In the case of such pay-TV-systems, system subscribers which have a contract with the transmission station shall be able to receive on their respective receivers the correct sound and pictures of a selected transmitted program, whereas those receivers which belong to house- holds which do not have such a contract shall be unable to see the transmitted program.

Different methods have been proposed for processing TV- signals or video signals that are transmitted on so- called pay-TV-systems, with the intention of preventing non-subscribing receivers from receiving a clear or correct reception of such TV-programs, such that when the program is received by non-subscribing TV-apparatus or receivers, the pictures become distorted so as to prevent them from being seen clearly.

These methods are based on different kinds of signal encryption, or "signal scrambling", and several differ¬ ent encryption methods have been proposed to this end.

With the aim of achieving desired coaction or sympathy between a transmitter and a system-subscribed receiver, the invention is based on the known technique of provid¬ ing the transmitter with or causing the transmitter to coact with a signal scrambling device, whereas reεpec- tive system-subscribed receivers are provided with or preceded by a signal unscrambling circuit or device in which the signal scrambling device and the signal un¬ scrambling device are mutually adapted so that a scram¬ bled TV-signal transmitted from the transmitter is unscrambled to a corresponding degree, so as to restore the transmitted signal to its correct form, so that the correct lines and pictures and sound are received on the system-subscribed receiver, whereas non-subscribed receivers receive scrambled TV-signals with distorted lines and pictures, and possibly also distorted sound.

BACKGROUND ART

TV-signal transmission pay-TV-systemε of the aforesaid kind are known to the art in several different forms.

Present day systems are based on one of two fundamental requirements, these systems being designated a first system and a second system in the following.

One example of the first system is the present day MAC- system.

MAC stand for "Multiplexed Analogue Components".

By this is meant that the picture signal components, colour and luminance, are transmitted in time-multiplex in that time slot which is available for transmitting pixel related information (analogue signals).

An example of the second system is the commercially available PAL-system (alternatively the SECAM-system) . In the PAL-system, the picture signal components, colour and luminance, are transmitted simultaneously by means of a method which can be described as a frequency multi¬ plex system. (The luminance signal is transmitted on the baseband, whereas the colour information is^' transmitted on a carrier wave which, with respect to frequency, lies in the spectrum of the base band signal).

It is also known that TV-signal transmission pay-TV- systems which transmit in accordance with the MAC-system require each system-subscribed receiver to be connected to or to contain a signal-unscrambling device, or decod¬ er, which is adapted to the MAC-system.

It is also known that TV-signal transmission pay-TV- systems which transmit in accordance with the PAL-system require each system-subscribed receiver to be connected to or to include a signal-unscrambling device, or decod¬ er, which is adapted to the PAL-system.

It is also known that a large number of receivers sub¬ scribe to both pay-TV-systems which transmit in accor¬ dance with the MAC-system and pay-TV-systems which transmit in accordance with the PAL-system, and that each such receiver must then be provided with a first signal-unscrambling device which is adapted to the MAC- system and a second signal-unscrambling device which is adapted to the PAL-system.

It is also known that the MAC-system and the PAL-system described above by way of example use different methods for synchronizing transmitters and receivers in sympathy with one another.

This synchronization is necessary because all TV-systems (both MAC and PAL) utilize time multiplex transmission of information concerning the various pixels or picture elements involved.

Thus, the synchronization information shall inform the receiver as to when the signal for a given pixel can be expected.

Although no discrete division of the pixels is found horizontally, the principle reasoning is nevertheless correct.

In principle, the exact manner in which the synchroni¬ zing information is formed is unimportant. The only important criterium is that this information can be used to drive the clocks of the transmitter and the receiver at mutually the same speed and in time with one another.

In the case of the MAC-system, the synchronization information is integrated with components in the video signal which function to permit the transmission of data. Synchronization is effected because parts of the data signal always present a predetermined pattern in given time positions.

In the case of the PAL-system, the synchronizing infor¬ mation has the form of pulses which are clearly delimit¬ ed from other parts of the video signal in time. The information comprises pulses which define the beginning of a new line in the picture and pulses which define the start of a new picture (or more specifically a part image) .

In order to be able to control the availability of a program to a viewer, it must be possible to distort the picture signal in some way or another. This distortion

(scrambling) of the transmitted picture must be achieved in a manner which will ensure that only those receivers which are entitled to receive the program will receive the correct picture. Consequently, only the receiver which is entitled to receive the program shall be pro- vided with a facility for the type of distortion or scrambling selected at that instance.

DISCLOSURE OF THE PRESENT INVENTION

TECHNICAL PROBLEMS When considering the state of the known prior art and the aforesaid requirements and circumstances it will be seen that a qualified technical problem resides in the provision of conditions which will enable each system- subscribed receiver, both in the MAC-system and in the PAL-system, to be provided with a single signal- unscrambling device, or decoder, which is compatible to both systems.

It will also be seen that a technical problem resides in providing the possibility, with the aid of simple means, of transmitting several programs simultaneously with conditional receiving possibilities, for example a transmitted program which is coded in accordance with the MAC-system and a transmitted program which is coded in accordance with the PAL-system, with the provision that a receiver decoder which is common to both systems can be used and that the complexity in the decoder used is only marginally greater than the complexity of the individual decoder intended for a respectiove one of the aforesaid systems, and that the transmitting equipment used is only moderately complicated.

The transmission location, or the transmitter, is nor¬ mally a cable-TV-center (head-end), although it may also be an uplink station for programs transmitted via satel¬ lite, or a ground-based TV-transmitter for normal ether-transmitted TV-signals.

Another technical problem in this respect is one of realizing those measures and those changes required of transmitted, scrambled TV-signals in a system which will enable the signals to be readily transposed, so as to enable said signals to be unscrambled in a signal un¬ scrambling device adapted to another system.

Another technical problem is one of providing condi¬ tions, with the aid of simple means, whereby one and the same system can be used for scrambled transmission of tables in distorted PAL-signals and in distorted MAC- signals.

It will also be seen that a technical problem resides in realizing that one or more of the aforesaid technical problems can be solved by replacing those parts of the PAL-signal which do not constitute pixel information or information necessary for the PAL-signal in other respects with those parts of a MAC-signal which include the data signalling necessary for the transmission of the scrambled tables.

Another technical problem is one of realizing that when data signalling in accordance with the MAC-system is introduced and utilized in the unscrambling devices, it is necessary to utilize the synchronization principle for the MAC-system also for the PAL-signal.

It will also be seen that a technically qualified prob¬ lem is one of realizing that this simple adaptation can be made by transposing part of the scrambled TV-signals according to the PAL-system to signals according to the MAC-system, thereby enabling the use of a signal un¬ scrambling device which is adapted for scrambled TV- signals according to the MAC-system with a highly limit¬ ed and inexpensive complement, which has no great effect on the total price of the equipment, including the necessary signal-unscrambling device.

It will also be seen that a technical problem is one of realizing that this simplification can be achieved by selecting a minor proportion of the line signals accord¬ ing to the PAL-system and excluding or inhibiting this portion of the line signals and, instead, introducing a signal structure which is in sympathy with the MAC- system and which has an information content correspond¬ ing to, or at least essentially corresponding to the information content of the inhibited part of the line signals according to the PAL-system.

It will also be seen that another technical problem is one of realizing that this simplification afforded by inhibiting line signals in the synchronizing part of the PAL-system and instead introducing a data flow according to the MAC-system containing information which, among other things, includes the information required to reproduce the requisite synchronizing pulses.

Another technical problem in this respect is one of realizing the significance of inhibiting a first selec¬ ted part of the line signal according to the PAL-system in a first device and by including this device in con¬ trol logic, or controlling said device by control logic which, in turn, is controlled by a processor, and activating first connecting means, ia the control logic, which function to inhibit that time-section which con¬ tains the synchronizing part of the line signal accord¬ ing to the PAL-system, and by causing said control logic to activate a second connecting means for applying to a second, selected part with a signal structure according to the MAC-system, and to be controlled by said proces¬ sor which, as a result of activation of the second connecting means is able to supply to the second select¬ ed part the requisite information content in data form.

It will also be seen that another technical problem is one of realizing that scrambling of the aforesaid nature enables the use of a signal unscrambling or decoding device which is adapted to the MAC-system and which can thus receive the line-signal part transposed from the PAL-system, since the signal entering the unscrambling device is understood as a data flow and the unscrambling device will produce, in a known manner, the requisite synchronizing pulse, whereas the remainder of the line signal is allowed to pass to the receiver without being influenced by the unscrambling device.

It will also be seen that another technical problem is one of allowing a part of the line signal according to the PAL-system, or the whole of said line system, to be scrambled or encrypted in addition to the aforesaid scrambling of the synchronizing pulse of the MAC-system, and by unscrambling the scrambled system in an unscram¬ bling device or decoder adapted to the PAL-system, said unscrambling device or decoder being connected down¬ stream of the unscrambling device or decoder adapted to the MAC-system.

It will also be seen that a technical problem is one of providing constructively simple conditions for control¬ ling or selecting the receiver which is to receive programs available from the transmitter in the form of PAL-signals and to use a receiver decoder which is constructed essentially for conditional reception of D2- MAC-signals. A further technical problem is one of realizing the simplifications that are to be found by using the same technology for controlling the availability of a select¬ ed program to the viewer, irrespective of the transmiε- sion system used, and therewith to realize that the data signalling principles must be similar, although while taking into account that the data signal structures need not be precisely the same, but that the hardware used in a D2-MAC-decoder will suffice to interpret those signals which are included in the PAL-signal for data transmis¬ sion, synchronization and system identification.

SOLUTION The present invention affords a solution to one or more of the aforesaid technical problems on the basis of a TV-signal transmission pay-TV-εystem which includes a transmitter, a number of system-subscribed receivers, a number of non-subscribed receivers, and a signal trans¬ mission medium which connects the transmitter with respective receivers. The transmitter is provided with, or coacts with a signal scrambling device and respective system-subscribed receivers are provided with or preced¬ ed by a signal-unscrambling device, wherein the signal- scrambling device and the signal-unscrambling device are mutually so adapted as to unscramble an scrambled TV- signal transmitted from the transmitter and regenerate a signal in its correct form, so as to form picture- correct lines and pictures and possibly also sound, while those receivers which do not belong to the system receive distorted lines, pictures and possibly also distorted sound from the scrambled TV-signals. The invention is also based on the concept of transmitting over the signal transmitting medium not only scrambled TV-signals and line signals according to a first system, for instance according to a MAC-system, but also scram¬ bled TV-signals and line signals according to a second system, for instance according to a PAL-system.

The invention takes as its starting point the use of a signal-unscrambling device, or decoder, which is funda- mentally adapted to unscramble scrambled TV-signals transmitted in accordance with the first system, or in accordance with the MAC-system.

The present invention now enables signals belonging to the second system, the PAL-system, to be scrambled so that system-subscribed receivers for programs transmit¬ ted in accordance with the MAC-system can also receive programs that are transmitted in accordance with the PAL-system, with only small modifications to the εignal- unscrambling device adapted to the MAC-system.

To this end, it is proposed in accordance with the present invention that a first means is provided which will function to inhibit a first selected part of the line signals according to the second system, the PAL- system, and that a second means is provided which will enable a second selected part to be applied to the line signals according to the PAL-system with a signal struc¬ ture conforming to the first system, the MAC-system, and with an information content which corresponds to, or which substantially corresponds to the information content of the first selected and inhibited part accord¬ ing to the second system, the PAL-system, and wherein the same system is used for scrambled transmission of tables and keys for the second system as that used for scrambled TV-signal transmission of tables and keys of the first system.

By way of preferred embodiments which lie within the scope of the inventive concept it is proposed that the first selected and inhibited part of the line signals is comprised of a line-signal synchronizing part, and that the information content in the second selected part of the line signals includes, among other things, the information required to regenerate requisite synchro- nizing pulses.

It lies within the inventive scope of the invention for the fii.st system to comprise a MAC-system, particularly a so-called DMAC-system and D2 MAC-system, and the second system to comprise a PAL-system.

In order to enable signals transmitted in accordance with the second system, such as the PAL-system, to be encrypted and scrambled, there is provided a first means which is comprised of processor-controlled control logic which functions to activate first connecting means in a manner to inhibit the synchronizing part of a line signal; and by a second means which is comprised of said processor-controlled control logic and which functions to activate second connecting means in a manner to supply to said second selected part the requisite infor¬ mation content according to the first system, exempli¬ fied as the MAC-system.

It will be seen that each system-subscribed receiver equipped with a signal unscrambling or signal decoding device adapted to the first system is now able to re¬ ceive the line-signal part transposed according to the first system and to generate requisite synchronizing pulses via the decoder, among other things, while the remainder of the line signal is able to pass to the receiver without being influenced by said decoder.

It is also possible within the scope of the invention to allow part of the line signal according to the second system, or the whole of said line signal, to be coded and to effect decoding of this coded signal in a decoder which is adapted to the second system and which is connected downstream of the decoder adapted to the first system and intended to generate the synchronizing puls- es.

ADV NT ES Those advantages primarily afforded by the inventive pay-TV-syste reside in the provision of conditions which will enable a receiver adapted to the MAC-system, with signal-unscrambling device, to be modified at moderate costs on the transmitter-and-receiver side, to receive scrambled TV-programs transmitted in accordance with the PAL-system, with modifications to the decoder, so that scrambled tables transmitted by one and the same system and the handling of requisite keys, etc., are common to the two systems.

The primary characteristic features of the inventive TV- signal transmission pay-TV-system are set forth in the characterizing clause of the following Claim 1.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in more detail with reference to proposed embodiments thereof which include the significant characteristic features of the inven¬ tion, and with reference to the accompanying drawings, in which: Figure 1 is a greatly simplified illustration of trans- mitter equipment used to transmit, via satel¬ lite, scrambled MAC-signals with scrambled tables and the transmission of individual "keys"; Figure 2 is a greatly simplified illustration of a receiver station which includes a plurality of receivers;

Figure 3A illustrates the information content of a line signal according to the first system, which is constructed so that a part of its information content will be present in data form, and which is exemplified as a MAC- system; Figure 3B illustrates generally the signal structure of a line signal according to the second system, which is constructed so that its information content will be present in analogue form, and which is exemplified as a PAL-system; Figure 3C illustrates the form of the line signal for a modified PAL-signal according to the invention, in which the synchronizing part is present in data form in accordance with the first system shown in Figure 3A, whereas the remainder of the line information conforms to the second system shown in Figure 3B; Figure 4 is a block diagram illustrating the scra b- ling equipment significant to the invention and the transposition of the synchronizing part of the line signal; and Figure 5 is a block diagram for unscrambling signals according to the second system with the aid of a decoder adapted to the first system.

DESCRIPTION OF EMBODIMENTS AT PRESENT PREFERRED Figure 1 is a highly simplified illustration of a trans¬ mission station which includes a transmitting antenna 1 which is connected to two transmitters 2, 3 each of which is adapted to transmit scrambled signals to system subscribed receivers according to a first system, here¬ inafter referred to as the MAC-system by way of example, and which is able to transmit authorization messages and individual messages which serve as scrambling keys, via equipment 4.

The system also includes equipment 5 by means of which a subscription can be sold to and invoiced to those sub¬ scribers who belong to the system or those apparatus which belong to the system, and to operate the requisite customer services in other respects.

It will also be seen from Figure 1 that the transmitting antenna 1 transmits signals to a satellite 7, over a signal transmission medium 6, and that the satellite 7 transmits these signals to a receiver antenna 10, shown in Figure 2, over a second signal transmission medium 8.

The signals received by the receiver antenna 10, such as MAC-signals, are transmitted via a conductor 11 and a network 12 to an illustrated system-subscribed receiver 13, via a particularly adapted decoder 14 which is designed for MAC-signals and which is controlled with the aid of a so-called "smart card" 15.

Figure 2 also illustrates a non-system-subscribed re¬ ceiver 16, which although able to receive the coded MAC- signals is unable to comprehend these signals.

It is conceivable that the receiver antenna 10 illus¬ trated in Figure 2 will receive non-scrambled signals transmitted in accordance with another system, for instance the PAL-system, these signals passing through the conductor 11 and the cable network 12 to the non- subscribed receiver 16, which is able to comprehend these non-scrambled signals. It is also conceivable that the receiver antenna 10 will receive scrambled PAL-signals which can be comprehended solely by a system-subscribed receiver.

According to the present state of the art, it is neces¬ sary to connect the receiver 13 of the MAC-system to a decoder 14. When the receiver 13 belongs to the system for a program which has been transmitted in a form coded in accordance with the PAL-system, a separate decoder (not shown) is required, this separate decoder being constructed in essentially the same way as the decoder 14.

The invention is primarily intended to enable a receiver 13 which is system-subscribed not only for programs that are transmitted in a coded MAC-system but also for programs that are transmitted in a coded PAL-system, to comprehend, or receive, the programs of both systems with the aid of one and the same decoder 14.

The present invention thus relates to a TV-signal trans¬ mission pay-TV-system which comprises transmitters 1, 2, 3, a number of system-subscribed receivers 13 and a number of non-system-subscribed system receivers 16, and a signal transmission medium 6, 7, 8 which connects respective receivers, wherein the transmitters 2,3 are provided with or coact with signal-scrambling devices and respective non-subscribed system receivers 13 are provided with or preceded by signal-unscrambling devices 14, and wherein the signal-scrambling device and the signal-unscrambling device are mutually so adapted that a transmitted scrambled TV-signal is unscrambled in the device 14 so as to restore a signal to its correct form so as to construct straight lines, pictures and sound in the receiver 13, whereas the non-subscribed system receivers, such as the receiver 16, produces distorted lines, pictures and possibly sound from the scrambled TV-signals.

The reception of the signals in the receiver antenna 10 and the transmission of said signals to one and the same cable network 12 is based on the transmission of TV- signals over the signal transmitting medium 8 in accor¬ dance v;ith a first system, exemplified as a MAC-system, and TV-signals according to a second system, exemplified as a PAL-system, and where the signal-unscrambling device 14 is primarily adapted to unscramble the signals according to the first system, or the MAC-system.

In order to enable the features of the present invention to be more readily understood, the fundamental form of the line signals will now be described with reference to Figures 3A-3C. Figure 3A illustrates a line signal formed in accordance with the MAC-system. This line signal is comprised of a first part 20 which contains data in digital form and which, more particularly, includes information concerning the synchronizing sig¬ nal, and a second part 21 which includes analogue infor¬ mation which relates to the video signal, and in this case particularly to the chrominance of the video εig- nal, and a further part 22 which includes further ana¬ logue information and which relates to the video signal, and in this case to the requisite luminance. The infor¬ mation 20, 21 and 22 are mutually separate in time, as shown in Figure 3A.

Figure 3B is a simplified view of a line signal accor¬ ding to the PAL-system, said line signal including a line synchronizing pulse 30, a so-called burst 31, and a signal part 32 which relates to the picture information concerned (black-white-scale), intended to impart to the line different light shifts from left to right. The invention is based on the use of a system-subscribed receiver for programs transmitted in accordance with the MAC-system in a known manner, but with the decoder or the signal-unscrambling device required by the MAC- system modified so that one and the same receiver is able to decode the scrambled signals transmitted in accordance with the PAL-system with the aid of one and the sa>.\e decoder, when the receiver is a subscriber to the PAL-system.

As will be seen from Figure 3C, the fundamental concept of the present invention lies in the inhibition of the synchronizing pulse 30 shown in Figure 3B and the re¬ placement of this synchronizing pulse with data in digital form 25 corresponding to a part of the data information 20 present in the line signal shown in Figure 3A, with the remainder of the signal shown in Figure 3B intact with requisite burst 31 and requisite signal content 32.

The finesse with the invention is that the system for transmitting scrambled or coded tables and the handling of keys etc. is common to both MAC-signals and PAL- signals.

One conceivable system for key transmissions is the "Eurocrypt M" system, which utilizes a so-called smart card, i.e. a card of the size of a normal credit card and comprising a processor and a memory.

The data flow 25 in Figure 3C is supplied with the PAL- signal in a scrambling or encrypting equipment 40, the principle construction of which will be described below with reference to Figure 4.

The signal incoming from the receiver antenna 10 passes a satellite receiver 41 and is delivered, via a conduc¬ tor 42, to control logic 44, via a synchronizing separa¬ tor 43. The signal content in the signal section "a" in Figure 3B is inhibited in inhibiting equipment 45, at the same time as the data flow 25 which is to replace the signal part "a" is introduced into the control logic 44, via computer equipment 46. This data flow is added to the PAL-signal in addition equipment 47.

If further scrambling of the signal transmitted accord¬ ing to the PAL-system is required, this is achieved through equipment 48, wherein the PAL-signal, encrypted in one or more stages, is transmitted to the cable network 12 through a modulator 49.

The thus scrambled or encrypted PAL-signal reaches the signal-unscrambling or decoding device 14, which recog¬ nizes the structure of the data flow 25 and generates a synchronizing signal which is significant to the PAL- system, this synchronizing signal being added to the

PAL-signal in the unit 53. When the PAL-signal is fur¬ ther encrypted, the signal is decoded in equipment 52 with the aid of the table obtained from the decoder 14.

The first system may advantageously be a MAC-system, particularly a DMAC-system or a D2 MAC-system, and the second system may advantageously be a PAL-system, al¬ though it may also be a SECAM-systera and NTSC-syste .

It can also be established that the first device will comprise control logic 44 which is controlled by a processor 46 and which, through activation of the first connecting means 45, functions to inhibit the synchro¬ nizing part of a line signal, and that the second device is comprised of the aforesaid control logic 44, con¬ trolled by the aforesaid processor 46, and which, through activation of a second connecting means 47, functions to supply said second selected part with requisite information content, in data form.

It can also be established that a decoder 14 adapted to the first system, the MAC-system, is arranged to receive the line-signal part of the first system transposed in part i»ι accordance with the second system, the PAL- system, and, among other things, to generate the requi- site synchronizing pulse, while the remaining part of the line signal is able to pass without being influenced by said decoder.

It is also possible to allow a part or the whole of the line-signal and/or the sound-signal according to the PAL-system to be coded and to decode said signal in a decoder 52 adapted to the PAL-system and controlled by the decoder 14 adapted to the MAC-system.

It will be understood that the invention is not res¬ tricted to the aforedescribed exemplifying embodiments thereof and that modifications can be made within the scope of the inventive concept defined in the following claims.

Thus the first system can be other systems than the mentioned MAC-system and the second system can be other systems than PAL-system, SECAM-system or NTSC-system.

Claims

1. A TV-signal transmission pay-TV-system which in- eludes a transmitter, a number of system-subscribed receivers, a number of non-subscribed receivers, and a signal transmission medium which connects the trans¬ mitter with respective receivers, wherein the transmit¬ ter is provided with, or coacts with a signal scrambling device and respective system-subscribed receivers are provided with or preceded by a signal-unscrambling device, wherein the signal-scrambling device and the signal-unscrambling device are mutually so adapted as to unscramble a scrambled TV-signal transmitted from the transmitter and thereby regenerate a signal in its correct form, so as to form picture-correct lines and pictures and possibly also sound, while those receivers which have not subscribed to the system receive distort¬ ed lines, pictures and possibly also distorted sound from the scrambled TV-signal, and wherein line signals according to a first system (MAC) are transmitted via said signal transmission medium, c h a r a c t e r i z e d by a first means ( 44) which functions to inhibit a first selected part ("a")of the line signals according to a second system (PAL); a second means (44) which enables a second selected part to be applied to the line signals according to the PAL- system with a signal structure conforming to the first system, (MAC) , and with an information content which corresponds to, or which substantially corresponds to the information content of the first selected and inhib¬ ited part ("a") according to the second system; and in that the same system is used for the scrambled trans¬ mission of tables and keys for the second system as that used for scrambled TV-signal transmission of tables and keys of the first system.

2. A pay-TV-εystem according to Claim 1, c h a r a c¬ t e r i z e d in that the first selected and inhibited part ("a") is comprised of the synchronizing part of a line signal; and in that the information content of the second selected part includes, among other things, information necessary for reproducing requisite synchro¬ nizing pulses.

3. A pay-TV-system according to Claim 1, c h a r a c - t e r i z e d in that the first system is a MAC-system, particularly a DMAC or D2 MAC-system; and in that the second system is a PAL-system, SECAM-system or NTSC-system.

4. A pay-TV-system according to Claim 1, 2 or 3, c h a r a c t e r i z e d in that said first means is comprised of control logic which is controlled by a processor and which, when activated by a first switching device, functions to inhibit the synchronizing part of a line signal; and in that said second means is compriεed of said control logic, controlled by said processor, which through the activation of a second connecting meanse functions to deliver the requisite information content to said second selected part.

5. A pay-TV-εystem according to Claim 1, 2 or 3, c h a r a c t e r i z e d in that a decoder which adapted to the first system is intended to receive a line-signal part which is transposed to the first system and, among other things, to generate a requisite syn- chronizing pulse, whereas the remaining part of the line signal according to the εecond syεtem is able to pass without being influenced by said decoder.

6. A pay-TV-εyεte according to Claim 1 or 5, c h a r a c t e r i z e d in that a part of the line signal, or the whole of the line signal, and optionally the sound signal according to the second system is/are encrypted; and that decoding of said encryption is effected in a decoder which is adapted to the second system and which is controlled by the decoder that is adapted to the first system.