Transmission system for the transmission of information in a prescribed frequency band

PATENTS AND REGISTRATION OFFICE

EXPLANATORY WRITING no. 356 863 intci H 04 b 3/04

P.ans. No. 1202/69 Received on 29 I 1969

Validity day 29 I 1969

Ans. publicly available on 2 VIII 1969

Ans. published and the publication published on 4 vi 1973 Priority requested, from 1 II 1968 (Netherlands, 68 01502)

NV PHILIPS 'BULLETIN FACTORIES, EINDHOVEN, NETHERLANDS

Inventors »LE Zegera, Vilt Snijders ooh J Kullman, Eindhoven

Agent: S Åkesson

Transmission system with pulse pattern generators as well as transmitters and receivers

The present invention relates to a transmission facility comprising a transmitter and a receiver for transmitting information within a prescribed frequency band, the total information to be transmitted originating from a main information source and an associated auxiliary information source with a smaller information content than the main information source. The transmission of the information signals can take place directly or after modulation, eg amplitude modulation or frequency modulation.

In this transmission system, the auxiliary information signal is formed by a periodic pulse pattern located within the frequency band of the main information signal, but unrelated to this main information signal, which pattern originates from the auxiliary information source constructed as said pulse pattern in the transmitter. while in the receiver the main information signal and the pulse pattern located within the frequency band thereof and combined linearly therewith are fed jointly to a modulation device to which also the locally obtained pulse pattern originating from a local pulse pattern generator corresponding to the pulse pattern generator in the transmitter is applied. which for automatic phase correction is connected to a frequency determining means in the local pulse pattern generator.

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The present invention aims to provide a transmission system of the above-mentioned type, in which the exact transmission of the auxiliary information signal is also made possible in the transmission of the information signals by transmission paths in which the information signals are subjected to irregularly varying frequency displacements.

According to the invention, the transmission system is characterized in that the pulse pattern generator in the transmitter is connected to the input of a frequency modulator. whose output is connected to the linear combination device, while in the receiver the received information signals are fed to the modulation device through a frequency modulator.

The invention is described in more detail in the following with reference to examples schematically shown in the accompanying drawing.

Fig. 1 shows a transmission system according to the invention, while Fig. 2 shows a time diagram for explaining the transmission system according to Fig. 1.

Fig. 1 shows a transmission system according to the invention with a transmitter and a receiver for transmitting a call signal which is assigned to a frequency band with a width of 3.5 kHz. This transmission is performed using single sideband amplitude modulation. For this purpose, the call signal originating from microphone 1 is fed to a transmission path 4 in the transmitter after amplification in an amplifier 2 and through a low-pass filter 3 with a cut-off frequency of 3.5 kHz. An amplitude modulator 5 which is fed by a carrier oscillator 6 of 64 kHz and is provided with a single sideband filter 7 with a passband of 64.0-67.5 kHz is connected to the input end of this transmission path 4, while a selection filter 8, also with a passband of 64.0 - 67.5 kHz are provided at the output end of this transmission path 4, said filter being connected to an amplitude demodulator 9 which is fed with a downwave oscillator 10 of 64 kHz and is provided with a single sideband filter 11 in the form of a low pass filter with a cut-off frequency of 3.5 kHz. The call signal transmitted through this transmission path 4 to the receiver is fed to a reproducing device 13 after amplification in an amplifier 12.

In this system, not only call signals but also an address signal are transmitted to establish a connection between the transmitter and the receiver, which is characterized by a certain address, which receiver connects the display device 13 to the amplifier 12 by means of a switch 14 only when it receives its own address. The total information to be transmitted is thus of the call signal originating from the main information source in the form of a microphone 1 and the address signal originating from an auxiliary information source in the form of an address generator, the information content of the address signal being much smaller than the call signal.

In order to achieve a special effect in the described plant:

transmission of information in accordance with the master patent, auxiliary information signal is formed which serves as an address signal of a periodic pulse pattern located within the frequency band of 3.5 kHz assigned to the call signal ofcb which is not related to the call signal, which pattern originates from the address generator constructed as a pulse pattern generator. and which pattern is combined in the transmitter with the call signal in a linear combining device 16 without frequency separation and without time separation.

In the embodiment shown in FIG. 1 the pulse pattern generator 15 is constructed as a feedback shift register 17 with a number of shift register elements 18, 19, 20, 21, 22, the contents of which are shifted by a shift pulse generator 23 with a constant shift period T and with a module 2 adder 24 incorporated between the shift register elements 20 and 21. , wherein the output of the shift register 17 is connected on the one hand to the other input of the module-2 adder 22 and on the other hand to the input of the shift register 17 to which also a starting pulse source 25 is connected. The shift pulse generator 23 is formed by a central clock pulse generator 26 of 1.2 kHz, to which a frequency divider 27 with a division factor 2 is connected, which thus generates shift pulses with a shift period D of 1.67 msec. If, when switching on the pulse pattern generator 15, the starting pulse source 25 generates a starting pulse, the shift register 17 will start the generation of a series of pulses due to the feedback of said pulse series with a repetition period T, as explained in the main patent, where the shift register 17 in Fig. 1 has a length of T = (2⁵ - l) D = 31D. In the described embodiment, the pulse pattern at the output of the shift register 17 has the shape shown in Fig. 2, which pulse pattern in the described system is added to the call signal in the linear combining device 16 without frequency separation and without time separation at a level of e.g. 20 dB below the call signal.

In the receiver, the call signal and the pulse pattern located within the frequency band are fed to it divided and linearly combined with it in common to a modulation device 28, to which also the locally obtained pulse pattern is fed, which originates from a local pulse pattern generator 15.^r corresponding to the pulse pattern generator 15 in the transmitter, the output of the modulating device 28 being connected to a smoothing filter 29, which for automatic phase correction is connected to a frequency determining means 30 of the local pulse pattern generator 15 '.

In the receiver shown in Fig. 1, the local pulse pattern generator 15 'is constructed in the same way as the pulse pattern generator 15 in the transmitter, the corresponding elements being provided with the same reference numerals but with an index regarding the receiver side. Furthermore, the modulation device 28 is formed by a module -2 adder 31 which is preceded by a limiter 32, which converts the received information signals into a divalent signal. The second input of the module-2 adder 31 is connected to the local pulse pattern generator Ιδ ”while the output is connected to a smoothing filter in the form of an integrating network 29, the output voltage of which controls a frequency correction device 30, constructed e.g. as a variable reactance, which is connected to an oscillator 26 'which is used as a local clock pulse generator. To the module 2 adder 31, on the one hand, the received information signal consisting of the call signal and the pulse pattern used as the address signal is supplied, and on the other hand the local pulse pattern which in shape but not in phase corresponds to the pulse pattern generated on the transmitter side.

As described in detail in the main patent, an integration voltage will be generated at the output of the integrating network 29, which voltage due to the lack of connection between the call signal and the pulse pattern, in case of coincidence between the locally obtained pulse pattern and the pulse pattern generated on a transmitter side, assumes and in the case of mutual time offsets between the pulse patterns smaller than D is proportional to said time offsets but has a constant minimum value for larger mutual time offsets. By supplying said integration voltage as control voltage to the frequency correction device 30, an exact phase stabilization of the local clock pulse generator 26 'to the phase position of the pulse pattern generated on the transmitter side is obtained.

The increase of the integration voltage which occurs in the integrating network 29 in the event of coincidence and which according to the foregoing forms an indication of the stabilization of the local clock pulse generator 26 'is used simultaneously for controlling the switch 14 preceding the display device 13. For this purpose, the integrating network 29 connected by a threshold device to the control circuit of the switch 14. In this way, the connection between the transmitter and the display device is obtained only when the reception address signal characterizes the receiver.

In the transmission system described so far, the address signal is thus transmitted in the call band without frequency separation and without time separation, the speech quality nevertheless being only slightly affected by the address signal which has a very low level, e.g. 20 dB below the level of the call signal.

Difficulties have been found in the practice of transmitting the information signals through transmission paths in which the information signals are subjected to irregularly varying frequency offsets, which e.g. in the case of the single sideband transmission system shown in Fig. 1 may be caused by irregular differences in the carrier frequencies of the waveform oscillators 6 and 10 at the input and output ends of the transmission path 4, which differences may amount to e.g. to 100 periods in lower quality transmission paths In particular, it has been found that the transmission of the pulse pattern acting as an address signal is adversely affected by these irregular frequency shifts.

In order to achieve a reliable transmission of the pulse pattern in the transmission system described, also by transmission paths in which irregular frequency shifts of the information signals occur, in the transmission system according to the invention the pulse generator 15 in the transmitter is connected to the input of a frequency generator. the linear combining device 16, while the received information signals in the receiver are fed through a frequency demodulator 34 to the modulation device 28.

In the embodiment shown, the frequency modulator 33 is formed by two AND gates 35,36, the outputs of which are connected through an OR gate 37 to the linear combining device 1 $, the pulse pattern originating from the pulse pattern generator 15 being fed to both AND gates 35,36 through supply lines, one of which is provided with an inverting device 38, wherein the first carrier oscillation derived from the central clock pulse generator 26 is fed to one of the AND gates 35,36 and a second carrier oscillation also derived from the central clock pulse generator 26 is fed to the second AND gate. In particular, the first carrier oscillation is fed with a frequency of e.g. 2.4 kHz, which is derived from the central clock pulse generator 26, by means of a frequency multiplier 39 to the AND gate 35, while the second carrier oscillation with a frequency of 4 · θ^χ· Equal to 1.2 kHz, is fed to the AND gate 36, for which purpose the series of clock pulses generated by the central clock pulse generator 26 is used directly in this case. The frequency demodulator 34 on the receiver side is formed e.g. by a Foster-Seely discriminator.

In the transmission system according to the invention, the pulse pattern which acts as an address signal is transmitted from the pulse generator 15 by means of frequency shifts. Depending on the presence or absence of a pulse in the divalent pulse pattern to be transmitted, a pulse series with a carrier frequency f gate 37, or through AND gate 36 and OR gate 37. The frequency modulated pulse pattern obtained at the output of the frequency modulator 33 is located within the frequency band of 3.5 kHz which is assigned to the call signal and is added at a level of e.g. 20 dB below the level of the call signal in the linear combining device 16 to the call signal without frequency separation and without time separation. In the receiver, the call signal and the frequency modulated pulse pattern located within the frequency band assigned to the call signal and linearly combined therewith are fed, common to the frequency demodulator 34. The pulse pattern originally generated on the transmitter side and the frequency demodulated call signal then appear at the output of said demodulator, which signal as well as the original call signal has nothing to do with the pulse pattern. the method described above.

If in the transmission system according to the invention irregularly varying frequency offsets occur in the transmission wall 4, the phase stabilization of the local clock pulse generator 6 'to the phase position of the pulse pattern generated on the transmitter side is generally not adversely affected by the irregularly varying frequency distortions. These irregular frequency shifts of the frequency modulated pulse pattern result in irregular amplitude variations of the demodulated pulse pattern at the output of the frequency demodulator 34, for which variations the described automatic phase correction coupling itself is already very insensitive. . Furthermore, a capacitor 40 located in front of the limiter 32 is incorporated to block the DC voltage generated by a constant frequency shift at the output of the frequency demodulator 34. If the measures according to the invention are not carried out, these frequency shifts would give rise to considerable and irregular pulse distortions in the received pulse pattern due to the mutual phase shifts in the components in the pulse spectrum, whereby on the one hand the reliability of the transmitted pulse pattern decreases. side margin for disturbances that are already small, when the transmission of information signals takes place through transmission paths with less satisfactory goodness, it is still reduced.

By applying the measures according to the invention it is achieved that even by transmission paths, in which irregularly varying frequency offsets occur, a reliable transmission of the address signal takes place without frequency separation and without time separation within the frequency band for the call signal, while also due to the completely digital structure. on call quality can be significantly reduced.

The influence on the call signal, which is already small due to the low level of the frequency modulated pulse pattern, can be further reduced by feeding the local pulse pattern in the receiver also to a frequency modulator 33 ', which is designed and controlled in the same way as the frequency modulator 33 in the transmitter, and in which the corresponding element in the figure has been denoted by the same reference numerals, but provided with an index on the receiver side, and by subtraction in a linear difference generator 41 of the locally obtained, frequency modulated pulse pattern from the received information signals. Due to the completely digital structure of the frequency modulators 33, 33 'and the exact phase stabilization of the local clock pulse generator 26' to the phase position of the pulse pattern generated on the transmitter side, the frequency modulated pulse patterns appearing on the outputs of the frequency modules 336, 33 'are always the same. and phase mode, whereby the effect of the address signal still remaining after the difference generation is greatly reduced. In addition, the offset of the effect of the remaining residual address signal towards higher frequencies in the frequency spectrum allows a further reduction with the use of a network cutting off the higher frequencies 42. A corresponding, the higher frequencies accentuating network 43 must then be used for the call signal on the transmitter side.

In the transmission system according to the invention, the address signal is thus transmitted in the call hand without frequency separation and without time separation, and a reliable transmission of the address signal also takes place for transmission paths which cause organically varying frequency shifts of the information signals. the remainder of the address signal at the input of the reproducing device 13 remains 50 to 60 dB below the level of the call signal.