DE1013691B - Television system for the transmission of two different programs - Google Patents

Description

GERMAN

The invention relates to a television system in which always two different programs with the help of one single amplitude-modulated signal with constant frequency and with one positive and one negative different half-waves are transmitted and this signal is a carrier wave with a higher frequency modulated.

In such a system, one of the signals to be transmitted, which is given by the function f _x (t) , is converted by means of a subcarrier wave with a frequency f ₀ = cu _o / 2 π in a mixer, which has the product ΟΙ = Φ _χ ( t) delivers [1 + 2 cos ω _ο ί]; this stage is followed by a low-pass filter which _{limits the transmitted frequency band to eu o} / 2, while the other signal to be transmitted, which is given by f ₂ (t) , is converted by means of the same subcarrier wave in another mixer stage which has the product σ ₂ = Φ ₂ {ί) [1 - cos 2 co ₀ t] yields and a low pass filter follows the likewise / π limited the transmitted frequency band to co _0. 2 The signal Φ _χ (ί) is equal to the original signal f- ^ t) minus the crosstalk, which is essentially due to the second signal, possibly multiplied by a suitable factor; this crosstalk would interfere with the reception if no suitable correction were provided. The signal Φ ₂ (ή is equal to the original signal f ₂ (t) minus the crosstalk and, if necessary, multiplied by a suitable factor; this crosstalk would also interfere with the signal under the same reception conditions. In a known way, the sum Σ = Cr ₁ + (- σ ₂ ) = (T ₁ - σ _{2 formed} in a suitable stage, followed by a low-pass filter that limits the frequency of the components to be transmitted to ω _ο / 2 π . The signal Σ is taken from the output of this filter and used for amplitude modulation The system can also work with direct amplitude modulation of the positive half-waves of a subcarrier wave with a frequency ω _ο / 2 π by the signal Φ _χ (ί), which is based on the signal f _x [t ), as mentioned, is related, and the negative half-wave by the signal Φ ₂ {ή, which is related to the signal f _s {t), as mentioned above; this carrier wave is also generated by known means and serves to modulate, in a known manner, the carrier wave transmitted by a transmitting antenna.

This transmission system has the advantage that, during reception, a particularly sharp and simple separation of the two original signals f _x [t) and f _z (t) can be carried out in accordance with their opposite polarity. After the familiar. The demodulation of the carrier wave captured by a receiving antenna is carried out in a manner that separates the subcarrier wave with the frequency ω _ο / 2 π , and two elements with an unbalanced television system for transmission
two different programs

Applicant:

NV Philips' Gloeilampenfabrieken,
Eindhoven (Netherlands)

Representative: Dipl.-Ing. K. Lengner, patent attorney,
Hamburg 1, Mönckebergstr. 7th

Claimed priority:
France 5 November 1953

Louis Ie Blan, Paris,
has been named as the inventor

Conductivity in parallel with opposite direction of flow are sufficient to use this auxiliary wave separate positive half-cycles into one channel and the negative half-cycles into another channel.

After renewed demodulation, signals are obtained in this way in the two channels which, after the crosstalk correction at the transmitter has taken place, are proportional to the original signals f- ^ t) and f ₂ (t).

If the system is used for television purposes, it is preferably assumed that the original signals f ^ t) and f ₂ {t) correspond to the image signals of two transmissions of different black-and-white television programs or two monochromatic components of a single color or stereo television transmission. It is assumed that a reference level, for example the black level, or auxiliary signals, for example line or frame synchronizing pulses, is separated on the transmitter side and the separation on the receiving side, in accordance with the practice customary in this technology.

Although there are various ways of doing this, in practice the reference level generally used is Black level is used, which e.g. with positive modulation at a carrier amplitude of 25 to 30% and with negative modulation at an amplitude of this wave of 70%. In the former case (positive modulation) As is known, the brightness values of the successively generated image points correspond to the amplitudes between 25 or 30% and 100% of this carrier wave,

709 657/140

3 4

while the blanking signals correspond to the reference level of the carrier wave symmetrically on the side of the peaks, ie neither 25 nor 30 ° / ₀ ; finally, outwardly, modulated, while the complex signal σ ₂ , the sync pulses correspond to the amplitudes that are lower than the transmitted signal Φ ₂ derived from f _z , the same of the mentioned levels and up to the value zero of the carrier wave at their zero values, ie inward, the carrier wave mentioned can sink. 5 metrically modulated.

The television system according to the invention is thereby After the original image signals f _x (t) and f _z (t)

characterized in that a constant base level used on the transmitter side with regard to the crosstalk and on the transmitter side is maintained, has been corrected and the auxiliary signals of the blanking on which the carrier wave are both alternately positive level and the synchronization added, whereby and negative by means of the mentioned signal modulated io f _t in Φ _± and f ₂ in Φ ₂ , they will, and this level in absolute value at least punctured by the positive or negative half-wave of the maximum amplitude of the negative half-wave equal to a subcarrier wave with the frequency ω _ο / 2π ; or it is modulating the main carrier wave inward. modulate these two half-waves directly, whereby

The invention creates the means by which the final signals C ₁ and σ ₂ arise, the transmitter side of which fulfills the requirements set and, after passing through one of the receiving side, the various elementary signals low-pass filter to sum Σ = σ _χ + (- σ ₂₎ that the frequencies to co _0/2 π limited, are separated in accordance with their respective functions. Fig. 1 is shown. The signal Σ then modulates

Further details of the invention go from the symmetrical the two half-waves of the main carrier wave further description with reference to the drawings, corresponding to the schematic representation of FIG. 2a represent embodiments of the invention. 20 and 2b.

In the description it is initially assumed that the various signals

the various modulations are positive. regulated by known means in such a way that the change

Fig. 1 shows the different levels of the signals Φ _χ wrestling of the signal f _x (t) always within the interval and Φ ₂ with respect to the axis of the subcarrier shaft with (^ 1), (-4ο) ^{un (} l ^of fJt) always within the interval of the frequency ω _ο \ 2π, and 25 (- A ₁ ), (- ^ 4 ₀ ), these two intervals being

Fig. 2 shows the same level with respect to the axis of the (modulated) amplitude of the subcarrier wave be-main carrier wave (with a frequency of more than pull and also the vertices of the sync pulses ω _ο / 2 π) in such a way that both sides of the last mentioned practically in the case of positive modulation the axis of the mentioned subcarrier shaft lie on the zero level axis; correspond to this subcarrier wave.

Fig. 2 a relates to the special case in which the 30 According to the invention, the modulation depth of the two television signals to be transmitted is the same standard main carrier wave selected by the signal Σ , dard belong, and that the zero values (or the axes) of the subcarrier wave

Fig. 2b relates to the more general case in which, with the frequency ω _o / 2 π at a constant level Y, each of these two signals belongs to an individual standard on either side of the mentioned axis of the main carrier wave. In the former case the auxiliary signals and 35 are and this level is at least equal to the maximum, in particular the line and frame sync pulses have the same amplitude A ₁ (with the sync pulses) of the signal σ ₂ repetition frequencies, and they are in phase, which modulates the main carrier wave inside. For this purpose, various means are specified in the two signals to be transmitted (Φ _χ or Φ ₂ ), which are carried out on the transmission side, while in the second case the repetition side can be used.

frequency and the different phases of the in Φ ₁ and Φ ₂ 40 In a cathode ray oscilloscope one can completely independent of the auxiliary signals contained - eg the modulation of the main carrier wave by which are each other. Let signal σ ₂ appear alone. The picture is then that

The reference symbols denote the total duration T1 of a negative modulation, the zero values of which coincide with the scanning or the formation of an image line which coincide with the maximum amplitudes of the modulated wave. Duration t _b the blanking period corresponding to the return 45 It is easy for the observer to make the necessary corrections to the scanning beam at the end of each line, t _s the duration, if this maximum of a line sync pulse, T ₀ the repetition values deviate from a reference straight line, the necessary period the puncturing impulses of the same to be marked on the screen of the oscilloscope carrying signal (ie the so-called puncturing can. This method has the advantage of a large single frequency). A ₁ denotes the maximum amplitude of the image fold, but always requires the presence of a signal f _x it) and A ₁ that of the image signal _{f 2} (t) ; A ₀ operating person.

draws the black level according to the signal You can also e.g. the modulation of the main

/ Ί (ί) and A ₀ the black level corresponding to the signal carrier wave on the screen of the cathode ray oscilloscope- / " ₂ (i). It can be seen that analog figures can appear graphs and would appear in front of this screen if signals for the whole arranging such duration of a perpendicular 55 monitoring means that a right scanning were reproduced (with successive image photoelectric cell of the screen hit lines). Only time intervals, when the axis of the sub-carrier wave is not H, the Tl, and t _s were then magnified . is in the correct position. The one generated by this cell

In practice, one can simply assume that current then automatically activates the required control A ₁ = A ₁ and A ₀ = A ₀ , ie that the two are switched over. However, this procedure is complicated, carrying image signals treated in the same way not very sensitively and not very precisely,
will. In a preferred embodiment of the invention

In Figs. 2 a and 2 b is further provided with Y, the amplitude is a simple, operationally reliable, automatic Vera Optionally which applied the two auxiliary carrier wave driving, which consists in that on the end Eder frequency _ω ο / 2 π corresponding level of the zero side in the signal Σ for modulating the main carrier value of the main carrier wave with a frequency of more wave level pulses and at the same time line synchronism than ω _ο [2π (preferably at least 10 times higher than pulses and / or image synchronizing pulses are introduced, ω _ο / 2 π) . if the two signals to be transmitted are the same

Figs. 2 a and 2 b show that the complex signal O _1, Standard correspond, or both the Zeilendas that transmits by f _x derived signal _Φ χ, the main 70 sync pulses of the main carrier wave on the inside

5 6

modulating signal or that of the signal f ₂ that is chosen such that outside of the eye-Fig. 2 a and 2 b derived signal are introduced, look, in which the level pulses are supplied, which, if the two signals correspond to different standards, instantaneous value of the signal a ₂ equal to Y - Φ ₂ (and inspoken. These signals generated by known means, special equal to Y - A ₀ immediately before the occurrence, which is periodic, e.g. with the frequency of the line synchronous 5 synchronous pulses). In addition, the resistor 14 pulses are supplied, a slightly shorter one bridged by a diode 16 to have the same polarity duration as the sync pulses themselves, with which they are used for the voltage Y to be kept in phase with the level of the axis by known means , the subcarrier wave being constant with respect to the axis of the main, the amplitude Y , so that the level -j- Y determines the carrier wave. The voltage obtained is modulo zero values of the subcarrier wave periodically, for example with io, for example the grid of the output stage 17. Let it be the line frequency that is applied. This level can be used for noting that it is not necessary to maintain the level pulses at line duration when low-pass filters are transmitted, which would otherwise be used without any further essentials, which would have a sufficient pass-through advantage, the main carrier wave temporarily suppressed range for the lowest frequencies of the transmitted ; therefore, according to the invention, they will have ribbon. 15 by similar pulses with the same frequency and FIG. 3 shows schematically the introduction of the auxiliary phase, but compensated with reversed polarity; signals into the image signal before puncturing and this is carried out, for example, by means of an auxiliary stage 18, formation of one of the modulation signals, e.g. O ₁ (the formation that works parallel to stage 17 on the anode side, but one of a second signal a ₂ is identical with the exception of the significant has lower output power and ent polarity), ie the formation of the part of the signal of the 20 speaking biased by the reversed sign-Fig. 1 above the axis. returned impulses is controlled.

According to this figure, for example, the signal Φ ₁ (which is derived from the anodes of the two stages 17 and 18 with that of the original signal f _x (t) after correction of the operating voltage source via a common impedance crosstalk) in stage 1 is at the level Danz 19 connected, and this is regulated up at this impedance, so that, as mentioned above, the value always 25 occurring signal is preferably fed to the antenna 21 via a filter 20 between A ₀ , which corresponds to the black level of the image, which has only a single filter Sideband and A ₁ , which lets through the level of maximum brightness.

is equivalent to. The sync pulses 2 with an amplitude If the two image signals f ₁ and f ₂ , which are simultaneously equal to or approximately equal to A ₀ , must be transmitted in an additional, two different standards borrowed level 3 added; the output signal of this stage 30, it follows that the sync pulse has a form 4 and then passes through the amplifier two signals generally not temporally combined stage 5, in which, as is known, the signal 1 + 2 coscu ₀ i fall. This is shown schematically in FIG. 2b, which causes puncturing; at the output of this stage, and in particular can be seen that it is sufficient that Zusammennach passage through the low-pass filter 6, which over- come the level pulses of the sync pulses changed ragene frequency band _ω ο / 2π limited, one obtains 35 jenigen to secure the signals to be transmitted which finally modulate the main carrier wave inside _{for the signal already indicated with Cr 1.} The level shown at 7. Pulses with the amplitude Y are then positive in Fig. 4 shows the form of a level pulse reproduced according to the "valleys" which correspond to the sync pulses invention and this signal.

Fig. 5 shows schematically the introduction of such a 40. A transmission device according to the invention is an example

Pulse into the subcarrier wave, which is used for modulation as shown in FIG.

Main carrier shaft is used. According to this figure, the signal Σ " at 22 is over

From Fig. 4 it can be seen that the pulse 10 to the capacitor 23, the resistor 24 in series with

Tuning of the level Y in phase with the synchronous a bias voltage source - V ₁ supplied. The this

impulses of the two signals Φ _χ and Φ ₂ and that the voltage taken from the resistor is eg the grid

Duration t / is slightly shorter than t _{s of} these pulses. the output stage 25 (identical to the stage 17 of Fig. 6)

Fig. 5 relates to the special case in which the two are fed in this way by the grid voltage

image signals to be transmitted are demodulated using the same standard. In parallel with resistor 24 is one

speak so that the sync pulses are provided with the same diode 26 in series with a resistor 27,

Frequency and phase can be received. In 50 whose bias voltage is - · V ₀ . The level pulses

In this special case, the level pulses would be the main to the resistor 27 via a capacitor 28

Suppress carrier wave for its duration, but the fed. Finally, the resistor 27 is through a

The invention provides means by which diode 29 bridges this effect.

is prevented. This device operates as follows: the signal Σ " at According to Fig. 5, the signals a _x and σ _{2 obtained} in the manner described 55 22 is at the input of the capacitor 23 to its mean values are set with opposite phase; at the junction of this condensation of a stage 8 supplied in such a way that the signal Σ sators and the resistor 24 it remains at the mean = O ₁ + (- σ ₂ ) is generated, which is set to a second additional value, which is supplied to stage 9 borrowed with the bias voltage - V ₁ is where the level of pulses 10 covers, when the diodes 26 or 29 are not present, are added at the output of this stage, a 60 result arises the presence of the diode 29th, the signal Σ 'indicated at 11 form, from Σ Level pulses which are fed to the anode, set only by the pulses 10 with an amplitude - Y , that the positive peaks (which distinguishes the one whose base 10 'is based on the same even sync pulses of the signal ls Φ ₂ correspond) to the line 12, which preferably correspond to the axis of the potential - V ₀ , so that in the moments, the main carrier wave coincides. 65 in which these pulses are supplied, the potential This signal Σ ' is then the transmitter modulator to - the anode of the diode 26 is also equal - F ₀ . Out of the one shown in FIG. 6. Time intervals between two successive levels - According to this Fig. 6, Σ ' pulses through the capacitor 13, but the anode potential of the diode 26 is fed to the resistor 14, the other end of which is lower (in an absolute value higher) than - F ₀ - Y connected to the negative pole of a voltage source 15 70 If there is no diode 26, the synchronous level of the Si

Claims (7)

7 8 gnals Φ ₂ at the junction of the capacitor 23 and its sync pulses are directed positively, via a of the resistor 24 must always be lower than the capacitor 35 of the control electrode of a cathode y , γ _< γ amplifier stage 36 supplied. To reintroduce the ¹ ° "DC component is the When the diode is, however, 26 is provided in a known manner, it is 5 parallel circuit of a Gitterableitwiderstandes and conductive, respectively, when the device uses a-level pulse of a diode which receives a proper bias voltage and then the potential of the supplied at the input The bias voltage and the characteristic curve of the resistor 24 to the value -F ₀ during the eye tube are selected in such a way that the peaks of the synchronous gazes are reduced, which correspond to the duration of such a pulse pulses practically at one of the cathode potential of those, such as In other words, they correspond to the level corresponding to a synchronous tube 36 and the black pulse of the signal Φ _2. The most negative levels almost coincide with the cut-off point of the characteristic curve values of Σ " are therefore at the constant level. The signal occurring at the cathode resistor 37 of the tube 36 - F ₀ - Y, which is higher than the negative shoulder, in which the sync pulses that is level pulses, during which the diode 26 is also directed positively, the cathode of the diode 38 does not conduct . 15 supplied. Between the anode of this diode and earth, the invention can of course also be carried out with the series connection of an i? C network 39, negative modulation of the subcarrier wave. 40 and a positive bias source. The pre-fig. 8, which corresponds to FIG. 2, shows that the same voltage of this source is selected in such a way that the Di method and the same device as mentioned above can still be used when synchronous occurs. It is sufficient, for example, that 20 pulses are conductive, but are non-conductive when a trap, level pulses with an amplitude Y - A _1, too strong a positive signal occurs. As a result, the result is that periodically the lower shoulders of the synchronous impulses of the signal, apart from those already in the control grid circuit of the tube 36, are determined, which positively modulates the main limitation and an additional limitation for the carrier wave inside. In the case of negative the occurrence of interference signals. Modulation of the subcarrier wave and the main carrier 25 When a sync pulse occurs, the wave can according to the invention as above before diode 38, and the capacitor 39 charges in such a way that are gone, but at the beginning of the signals the anode potential of the diode drops. As a result, will 1 - Z ₁ (i) and 1 - f ₂ (t) instead of the signals f _x (t) and with a suitable choice of the time constant of the .RC network f _% {t) can be used. Factory 39, 40 the diode 38 for a certain time. required, not just the two original signals f ^ t) The parts of the occurring after this sync pulse and f ₂ {t), which are not used by the diode 38 during the transmission to form the more or signal voltage less complex modulation signals are used. In parallel with the network 39, 40 is one separate from each other, but also the special limiting circuit of a diode 41 and a pre-auxiliary signals, in particular the sync pulses, from 35 voltage source V _s attached to the level of the pre- isolate this. voltage across the network 39, 40 to limit. the The separation of the time constant of the network 39, 40 after the first demodulation is z. B. that held signals occurs according to their polarities versus twice the pulse repetition period. Between The voltage drops over the axis of the subcarrier shaft, which occurs when two successive pulses are switched off Transmission, as stated above, constant level 40 of the capacitor 39 then not in the absolute value is held and on the receiving side by a below 0.6 V _s . appropriate circuit is restored; a part of this is thus obtained at the terminal of the capacitor 39, the circuit holds the black level of the signal which is connected to the anode of the diode 38, modulates a main carrier wave inside, and another potential curve, which is shown in FIG is, the equal part of the corresponding sync level. The latter 45 is considered early with FIG. 10. Fig. 9 shows at a measure the axis of the subcarrier wave is periodically puncturing pulses of the video signal f ₂ , which are held by with the same repetition frequency as on the limitation to the level Vj ₃ from pulses with a larger transmitter side. Result in amplitude, and at b pulses which correspond to the blanking The device provided for this purpose is shown in FIG. 10; these have an even position. 50 plitude F _s = Vt, and are not limited; at c According to this figure, the antenna experiences the missing pulses. The period of the absence corresponds to the recorded signal a suitable gain in one of the duration of a sync pulse, e.g. B. a line high frequency stage 30 and then a first demodulation pulse, during which the signal Φ _{2 down} to zero. The signal 31, which decreases the resistor 32, whereby the puncturing pulses and thus also the modulator stage is fed, has, for example, the shape of 55 the subcarrier wave is suppressed. Signal according to FIGS. 2a or 2b. The separation of the signal shown in this figure has a signal according to their polarities is carried out, for example, by means of the uniform level during the duration of the synchronous two diodes 33 and 34, which have counter-impulses. It can then be connected directly in parallel for the set forward direction and synchronization of the deflection devices of the positive with the potential 4- V _{a can be} biased, which can be used 60 catcher. As indicated in the figure at 31, the axis of the auxiliary chronization remains fixed outside of the occurrence of the synchronous carrier shaft. The diode 33 transmits the main impulses to avoid the mentioned signal is again limited by a carrier wave outwardly symmetrically modulating signal. on one channel, and the diode 34 transmits to one. It can be seen that numerous variations of the circuitry other than the main carrier shaft inward 65, which are given to those skilled in the art, within the symmetrically modulating signal. (It will be possible within the scope of the invention assumed that the modulation is e.g. positive.) To get the sync pulses from the inner module claims: separation signal will continue to be the one on the 1st television system, in which there are always two different Anode of the diode 34 occurring demodulated signal, 70 programs with the help of a single amplitude modulated signal with constant frequency and with one positive and one negative from each other different half-wave are transmitted and this signal is a carrier wave with higher Frequency modulated, characterized in that a constant base level is used and on the transmitter side is maintained, with respect to which the carrier wave is alternately positive and on both sides is modulated negatively by means of the signal mentioned, and this level in absolute value is at least the Maximum amplitude of the negative half-wave is the same, which modulates the main carrier wave inward. 2. Television system according to claim 1, characterized in that a cathode ray oscillograph used at the transmitter to indicate the modulation of the carrier wave by the half-wave that the Carrier wave modulated inward only, and means are provided by which the modulation depth can be changed and adjusted manually if the The maximum amplitude of the modulated wave is no longer on a horizontal, straight line. 3. Television system according to claim 2, characterized in that the manual operation by a automatic operation by means of photo-electric cells is replaced by the one on the tube screen appearing image must be taken by suitable safety gears. 4. A television system according to claim 1, wherein said two programs are of the same standard correspond and have temporally coincident sync pulses, characterized in that the Carrier wave signal negative pulses are added, which hold the base level, which results from the Value of the horizontal sync pulses results, and that the carrier wave on it by the total signal is modulated, which is formed by the aforementioned carrier wave signal and the aforementioned pulses. 5. Television system according to claim 4, characterized in that to avoid suppression the carrier wave during the PegeHimpulse a continuous wave with sufficient amplitude generated during the same time. 6. The television system of claim 1, wherein the sync pulses of the two programs are not necessarily coincide in time, characterized in that the level of the multiplex signal on a suitable value during the occurrence of the sync pulses of one of the two programs by means of an electron tube system that is scanned by pulse voltages. 7. Television system according to claim 1, characterized in that the receiver after the demodulator stage contains a stage which, on the one hand, limits the signal to suppress the the Carrier wave outward modulating program brings about and on the other hand a voltage threshold value generated, which serves to separate the sync pulses from the image signals that the carrier wave modulate inwards. For this purpose 2 sheets of drawings © 709> 657 / 140- 8.