WO2009101357A1

WO2009101357A1 - Method for receiving wireless telecommunication using the single sideband amplitude modulation technique

Info

Publication number: WO2009101357A1
Application number: PCT/FR2009/050215
Authority: WO
Inventors: Albert Bertrana; José Maria GOMEZ CAMA; Santiago Marco Colas; Aitor Osorio Marti
Original assignee: Albert Bertrana; Gomez Cama Jose Maria; Santiago Marco Colas; Aitor Osorio Marti
Priority date: 2008-02-15
Filing date: 2009-02-11
Publication date: 2009-08-20
Also published as: FR2927746B1; EP2253068A1; FR2927746A1

Abstract

The invention relates to a method whereby an intermediate frequency signal (PIA) is triggered by heterodyning with a local mixing signal, the intermediate frequency signal is filtered through a bandwidth corresponding to the side band containing the useful information, and the signal obtained in this way is subjected to an envelope detection for SSB by means of a locally generated carrier for SSB for extracting the useful information. According to the invention, the signal produced by the heterodyning is subjected to a frequency discrimination in order to extract a signal for restituting the highly attenuated carrier in the telecommunication received. The frequency of the restitution signal is identical to that of the residue following the heterodyning of the highly attenuated carrier. The restitution signal of the carrier is then used to reduce the deformations that can affect the reception of the useful information band.

Description

Method of receiving a wireless telecommunication using single-sideband amplitude modulation technique

The present invention relates to the field of wireless telecommunications using the technique of amplitude modulation "single sideband" (abbreviation in French "BLU" and English "SSB").

Figure 1A of the accompanying drawings shows, as a reminder, the frequency spectrum of a normal double-sideband normal amplitude modulation (AM) transmission with respect to a PHF carrier.

Referring to FIGS. 1 B to 1 D, it can be seen that the AM and SSB modulation technique essentially consists, on transmission, in amplitude modulating (AM) a high frequency carrier wave PHFA which is suppressed on transmission or strongly attenuated (here, for example, that at 27.185 MHz of channel 19 of the "citizens" radio frequency

"Citizen Band" or CB) that can be modulated by useful information (human voice or other information) that can be contained in one of the two sidebands, respectively a lower sideband (BLI or LSB in English) and a upper sideband (BLS or USB in English).

According to the standards defining the CB with a channel spacing of 10 kHz, these bands shall have a width of 2.7 kHz each (0.3 to 3 kHz, equal to the transmitted voice band) and a bandwidth requirement total BT of 8.5 kHz to which may be added margins of 1, 5 kHz it has in common with adjacent channels. Harmonics and other modulation products may spread over BH bands with a width of 2.75 kHz at the end of each sideband. The standards also tolerate a frequency error of the PHFA carrier (and consequently also the sideband) in each channel which for the CB is +/- 0.6 kHz.

As can be seen in FIGS. 1B to 1D, during a BLU transmission, only one of the BLI or BLS sidebands is sent to the transmitting antenna, having taken care in the transmitter of " delete "the carrier itself or at least considerably attenuate it by up to 30 dB or more (attenuated carrier PHFA). In this way, in the same transmission channel, one may be in the presence of a single sideband (BLS for Figure 1 B and BLI for Figure 1 C) or two sidebands at a time (the BLI and BLS bands of Figure 1 D). In the latter case, the attenuated carrier PHFA is double coming from two transmitters, one working in BLS and the other in BLI whose carrier waves may have identical or slightly different frequencies.

In known manner, this mode of emission has considerable advantages residing in particular in a saving of energy ("absence" of carrier) and a greater scope of telecommunication. It will be noted that in FIGS. 1A to 1D and also in FIGS.

4B analyzed below, it is assumed that the modulation in each sideband is at maximum, which is symbolized by vertical hatching. As a widespread application of this technique, mention may in particular be made of the CB telecommunication already mentioned. It should be noted, however, that the invention can be applied to all radiocommunication services in which the single sideband technique with high carrier attenuation is used, such as professional maritime, aeronautical or other telecommunications, or telecommunications radio amateurs, for example. The invention therefore applies to all radio telecommunications using AM with SSB.

Referring to FIG. 2 of the accompanying drawings, it will be seen that a conventional receiver capable of receiving a single side-band and carrier-canceling transmission includes an antenna 1 picking up the signal transmitted from a transmitter (not shown ). The signal of this antenna 1 is injected into a frequency converter mixer 2 where it is combined with a heterodyning signal generated in a local oscillator 3. The latter is adjustable not only to tune the receiver to the desired telecommunication channel by a adjustment device 4, but also to be able to select the desired sideband by means of a selector 5. Moreover, the oscillator 3 has a fine adjustment of its frequency called

"Clarifier" symbolized by the arrow 6. The output signal of the mixer 2 is applied to an intermediate frequency pass filter 7 having a center frequency F 1 and a bandwidth corresponding to a sideband. For CB for example, this bandwidth, with its margins, can be equal to 4.4 kHz. The known receiver also comprises an intermediate frequency amplifier 8 and an envelope detection circuit for SSB 9 whose output produces on a terminal 10 the signal corresponding to the useful audio information which is contained in the signal arriving on the antenna 1. This useful information can then be processed in conventional low frequency circuits (not shown) to be audible.

To enable detection, there is provided a local oscillator 11 for substitution of the intermediate carrier whose output signal is used in the envelope detection circuit for SSB 9 receiving the amplified output of the amplifier 8. The operation of this conventional receiver can be adversely affected by several types of errors or drifts relating in particular to the frequency. First of all, the standards generally admit a frequency error on the carrier of the transmitter which for the CB for example is +/- 0.6 kHz. Moreover, there may be an error or frequency drift of the received transmission due, for example, to an instability of the carrier oscillator of the transmitter. Moreover, the local heterodyning oscillator 3 of the receiver may also have a frequency error and a drift due, for example, to temperature variations. The resultant of these errors and frequency drifts is present in the intermediate frequency signal F1 at the output of the mixer 2. As a result, the sideband of audio information may be off-center in the bandwidth of the filter 7 (it is possible to lose part of the components of the received audio information). But the difference in frequency between this sideband and the attenuated carrier that accompanies it is not changed compared to the signal received by the antenna (the frequencies of the received audio information will be respected and maintained).

This deformation caused by these errors and drifts in frequency will be called later "type A deformation". Similarly, the oscillator 11 of substitution of the intermediate frequency carrier can have its own errors and drifts in frequency. In any case, if the frequency of this substitute carrier is not identical to that of the attenuated carrier delivered by the mixer 2, a significant change in the frequencies of the received audio information occurs on detection. which can make the voice unintelligible. This deformation caused by the difference in frequency between the original intermediate carrier and this substitution carrier generated by the oscillator 11 (modification of the frequency difference between the substitute carrier and the sideband), will be called thereafter " type B deformation ". For the understanding of the vocal information, it is more important than the type A deformation.

As is well known, heterodyning consists in summing the frequency range received with a local frequency originating from oscillator 3 in order to obtain a frequency sideband composing the information received centered on the fixed bandpass filter 7 This is why the oscillator 3 heterodyning frequency has a fine manual setting (the clarifier 6) so that the operator can adjust it, while listening to the received audio information. This makes it possible to avoid type A deformations. However, this also makes it possible, and above all, to obtain, in order to avoid type B deformations, that the difference in frequency between this lateral band and the substitution carrier generated in the oscillator. 11 the same as that existing between this sideband and the attenuated carrier of origin.

FIGS. 3A and 3B illustrate the case of an almost perfect reception of a telecommunication in which the frequency band containing the useful audio information is correctly centered on the bandwidth of the filter 7. In FIG. 3A, the bandwidth BP thus coincides with the lower lateral band BLI, whereas in FIG. 3B, it is the upper lateral band BLS of the received channel which coincides with the bandwidth BP of the filter.

Taking again the example above concerning the channel 19 of the CB, we see that the bandwidth BP of the filter 7 is 4.4 kHz at 0 dB and 5 kHz at - 40 dB, centered on a center frequency FC of 10.695 MHz, for example. Under these conditions, to receive without any type A deformation, the lower sideband BLI of the channel 19, the local oscillator 3 must be set to a frequency of 16.4875 MHz so that the attenuated "carrier" intermediate frequency F1 is located at 10.6975 MHz. Thus, the band of useful audio information will coincide best with the bandwidth BP.

Conversely, if the user wishes to receive the upper sideband BLS (Figure 3B), it must adjust the local oscillator 3 on a frequency of 16.4925 MHz for this sideband is again in coincidence with the bandwidth This result is obtained by inverting the switch 5 which makes it possible to obtain a frequency offset of 5 kHz from the oscillator 3. This same switch also controls a 5 kHz offset of the surrogate carrier oscillator 11. .

The two examples which have just been studied correspond in fact to ideal cases in which the oscillators produce frequencies at nominal values. These are cases that are rarely encountered in practice.

Thus, disturbances can affect the telecommunication between transmitter and receiver. For example, according to the standards in force, the oscillator of the transmitter and the local oscillator 3 can produce a carrier frequency with a certain tolerance which for the band CB is +/- 0.6 kHz. FIGS. 4A and 4B illustrate the deformation which can thus affect the reception of the useful audio information, if the transmitter comprises oscillators which produce a carrier frequency located respectively at one or the other end of the tolerance range of the transmitted frequency, the sum of these deviations can therefore be at most 1, 2 kHz.

In FIG. 4A, it is assumed that the upper sideband BLI must be received, again in the context of the example discussed above. If the oscillator frequency deviations accumulate, in the positive direction, the intermediate "carrier" frequency on which the receiver will be tuned, will then be shifted by 1.2 kHz relative to the frequency of the ideal case of FIG. 3A and the useful information tape will fall too far to the right of the tape In this case, there will be a considerable type A deformation of the reception of the useful audio information. In addition, if the frequency of the substitute carrier of oscillator 11 is at its nominal nominal value of 10.6975 MHz, it will not correspond to the intermediate frequency of the original attenuated carrier and its difference in frequency relative to the components of the information sideband will be greatly altered and the frequencies of the voice information detected in the detector 9 will undergo a strong type B deformation which will make them unintelligible. Conversely, in the case of FIG. 4B, it is assumed that the frequency deviations of the oscillators accumulate in the negative direction. If in this case we want to receive the upper sideband BLS, the carrier frequency F1 will be shifted "to the left" of 1.2 kHz with also strong deformations of types A and B in the reception of the useful audio information band .

This shift will introduce a disturbance in the detection of useful audio information performed in the detector 9 which is conventionally connected to the oscillator 11, the latter having, for each received sideband, a fixed frequency. In the example studied, the frequencies are respectively 10.6975 MHz for the BLI and 10.6925 MHz for the BLS. Deformations of the same order may appear due to drifts, for example in temperature of the oscillators 3 and 11.

To remedy this, the conventional single-side and carrier-canceling receivers of the clarifier 6 have been endowed for a long time, which makes it possible manually to correct the various errors and drifts, and in particular to refocus the band of the signal applied to the filter 7 by a certain limit. report to the window defined by it. This manual clarifier also makes it possible to correct the defects due to deviations that the carrier frequency of substitution can undergo compared to the sidebands containing the useful information.

In practice, the clarifier is operated by means of a manual control button, which is necessary frequently during the listening and of course also whenever there is a change of transmitting station, even within the same frequency band, since each of these stations has, with a high probability, a distinct frequency drift. This need is particularly felt as the number of telecommunications between transmitters and receivers operating in the same frequency band is high.

In the field of CB used very often by truck drivers and motorists, the need for manual clarifier adjustment imposes the driver frequent handling that distracts from his main driving task thus impeding the safety of traffic. In other fields of use of single-sideband telecommunication and carrier suppression, the tedious handling of the manual clarifier, while it does not necessarily affect the security, nevertheless induces discomfort of use of the receiver. The object of the invention is therefore to create a method for receiving the single-sideband telecommunication with strong suppression or attenuation of the carrier wave which overcomes the type A and B strains analyzed above. It also aims to create a receiver for the implementation of this method. The invention therefore firstly relates to a method of receiving a telecommunication whose useful information is contained in a single sideband of a telecommunication channel whose carrier is greatly attenuated in the telecommunication transmitted, this method of generating from the received telecommunication signal an intermediate frequency signal by heterodyning with a local mixing signal, variable as a function of the frequency of the carrier of the telecommunication channel to be received, of filtering said intermediate frequency signal through a bandwidth corresponding to the sideband containing said information, - amplifying the signal from the filtration, locally generating a carrier and subjecting the signal from the amplification to an envelope detection for SSB using said carrier generated locally to extract said useful information from said signal from the amplification, characterized in that said signal from the heterodyning is subjected to a digital frequency discrimination to create a carrier restitution signal whose frequency will be identical to that of the residue after heterodyning the attenuated carrier of said transmitted telecommunication and using said carrier restitution signal to reduce the deformations that may affect the reception of the useful information band.

Thus, the invention is based on the consideration that the heavily attenuated carrier present in the telecommunication transmitted can be usefully exploited, because on reception this carrier, although weakened very strongly (of the order of 30 dB or more) remains present in the received signal and is found in the product of the heterodyning carried out in the receiver in the form of a highly attenuated intermediate frequency carrier. While in conventional BLU receivers with envelope detection, this intermediate carrier was neglected and rejected, the invention plans to use it effectively to ensure a better user comfort and in the field of CB in particular , to ensure improved safety for users of receivers in road vehicles. According to a first mode of implementation of this method, it consists in using said intermediate carrier restitution signal to perform said detection.

This characteristic of the method according to the invention makes it possible to avoid type B deformations, that is to say the most troublesome and common frequency drifts, such as in particular the variable frequency differences which may be manifest for a variety of reasons, between the single intermediate frequency sideband and the mixing carrier applied to the SSB detector. Indeed, thanks to the invention, the frequency of the restored carrier is identical to that of the intermediate frequency carrier which, according to the invention is copied.

According to an advantageous characteristic of the first embodiment which has just been defined, the method may further consist in generating a standard signal having a frequency equal to the nominal frequency of the carrier after heterodyning said intermediate frequency signal, comparing said intermediate carrier restitution signal with said locally generated standard signal to generate a comparison signal and adjusting the frequency of said local signal mixing according to said comparison signal.

This characteristic makes it possible, in addition to that defined above, to also compensate the type A deformations, in other words to avoid decentering of the useful audio signal with respect to the bandwidth of the intermediate frequency filtering.

However, according to a second embodiment of the method of the invention, the latter can also consist in generating a standard signal having a nominal frequency equal to the nominal frequency of the intermediate carrier after heterodyning said intermediate frequency signal to be used. said standard signal as carrier for the envelope detection, to compare said calibration signal with said carrier restitution signal and to adjust said local mixing signal according to the difference found in said comparison.

This second embodiment of the method also makes it possible to avoid both type A and type B deformations in the useful audio signal to be obtained.

In general, the method of the invention makes it possible to avoid any manual clarification operation during the listening of the audio signal.

According to a complementary advantageous characteristic of the invention that can be applied to the two embodiments that have just been defined, the frequency discrimination can be achieved by an algorithm that uses as data the module of a fast Fourier transformation. (FFT) on said intermediate frequency signal and the autocorrelation of this module with the digital form of this signal. Thus, thanks to the invention, the phase angle of the vector is not calculated because it has been found that it does not matter in the case of a SSB receiver by detection of envelope object of the invention. The invention also relates to a receiver for implementing the method as defined above, designed to receive a telecommunication whose useful information is contained in a single sideband of a telecommunication channel whose carrier is greatly attenuated in the transmitted telecommunication, this receiver being characterized in that it comprises: an antenna for sensing said telecommunication, an adjustable local oscillator for generating a local mixing signal, variable as a function of the frequency of the telecommunication channel to be received a mixer for generating an intermediate frequency signal by heterodyning with said local signal, an intermediate frequency filter having a bandwidth corresponding to the sideband of the telecommunication containing said information, an amplifier of the signal from said filter to provide an amplified signal , means to generate local a carrier, and envelope detection means for BLU to extract said useful information from said amplified signal using said locally generated carrier, characterized in that it further comprises a connected function block of a part for discriminating by digital processing in said signal from the heterodyning applied to said intermediate frequency filter, a restitution signal of the carrier whose frequency is identical to that of the residue after heterodyning the heavily attenuated carrier of said telecommunication transmitted and on the other hand to use said carrier restitution signal in order to reduce the deformations that may affect the reception of said useful information band. According to a first embodiment of this receiver, the output of said function block is connected to said envelope detection circuit for BLU for using said intermediate carrier restitution signal for detection.

In the case of this first embodiment of the receiver, the carrier restitution signal is thus used in place of the carrier generated locally in the conventional receiver by an oscillator.

According to another characteristic of this first embodiment, said local oscillator is advantageously an oscillator equipped with a frequency adjustment by a voltage and the receiver further comprises a standard oscillator intended to generate a standard signal having the nominal theoretical frequency of said intermediate carrier and an analog comparator of which one of the inputs is connected to said master oscillator and whose other input is connected to said function block and whose output is connected to the control input of said local oscillator in order to control it the frequency as a function of the result of the comparison made by said comparator between said standard signal and said carrier restitution signal.

According to a second embodiment of the receiver according to the invention, said local oscillator is an oscillator equipped with a regulation of its frequency by a voltage and said receiver further comprises a standard oscillator intended to generate a standard signal having the nominal theoretical frequency. said intermediate carrier, the output of said standard oscillator being connected on the one hand to said detection circuit for SSB and on the other hand to an input of said function block, said function block comprising means for comparing a digital value representing the frequency said standard signal to a digital value representing the frequency of the intermediate carrier and to apply the result of the comparison in analog form to the control input of said local oscillator.

In the case of these two embodiments of the receiver according to the invention, it can be provided in said function block calculating means which using an algorithm performs said frequency discrimination, said calculating means being connected means for performing fast Fourier transform (FFT) of said intermediate frequency signal, means for effecting the extraction of the module after this transformation and means for performing the autocorrelation of this module with the digital form of this intermediate frequency signal.

The invention is described in more detail with respect to exemplary embodiments and with reference to the accompanying drawings in which: FIG. 1A is a diagram illustrating the contents of a conventional dual sideband AM telecommunication; FIGS. 1B-1D are frequency diagrams illustrating the content of a typical single-side-band carrier attenuation telecommunication; FIG. 2 represents a simplified diagram of a conventional receiver for receiving telecommunications in SSB by envelope detection; FIGS. 3A and 3B show frequency diagrams illustrating the operation of a single sideband and carrier attenuation receiver in the case of a type-A-free reception of useful audio information contained in a telecommunication of a given channel of CB; FIGS. 4A and 4B show diagrams similar to those of FIGS. 3A and 3B in the case where certain organs of the transmitter and of a receiver operate at the limit of their cumulative frequency tolerances, also in the case of a channel given a telecommunication from the CB; Figure 5 is a schematic diagram of a single carrier-sideband attenuator receiver designed according to the invention; FIG. 6 is a simplified diagram of a function block ensuring the restitution of an intermediate carrier implemented in the receiver of FIG. 5; Figure 7 is a schematic diagram of a receiver according to the invention provided with another advantageous feature of the invention; FIG. 8 shows an advantageous variant of the receiver according to the invention; and Fig. 9 is a schematic diagram of a function block for the receiver of Fig. 8.

FIGS. 1A to 4B being already described above under the prior art, reference will be made immediately to FIG. 5 which represents a first exemplary embodiment of a receiver according to the invention.

This receiver comprises the elements 1, 2, 3, 7, 8 and 9 already described with reference to FIG. 2, the oscillator 3 being represented in a simplified manner, it being understood however that it comprises, like the conventional receiver, the setting 4 and 5 for the selection of the channel and the useful sideband in BLI or BLS. The clarifier 6 becomes optional in the context of the invention.

According to an essential characteristic of the invention, the receiver of FIG. 5 comprises means for restoring the intermediate frequency carrier F1 (FIGS. 3A to 4B) which is present in a strongly attenuated manner in the signal coming from the mixer 2. These means are symbolized by the function block 12 in FIG. 5. This unit receives the product of the mixture coming from the mixer 2 with an intermediate attenuated carrier PIA which is extracted from the signal by the function block 12 and once obtained and amplified, it is applied to the detector 9 in the form of a restored PIR intermediate carrier with respect to which the envelope detection of the wanted signal will be performed. Thus the detection will be made with respect to an intermediate carrier which will follow all the variations in frequency undergone by the attenuated carrier PHFA present in the signal coming from the transmitter and received on the antenna 1 (FIGS. 1B to 1D) and which will also follow the errors and frequency drifts of the local oscillator 3. This process makes it possible to avoid type B deformations that can affect the detection of useful audio information without any manual intervention of the user, distortions that were conventionally due firstly to shifts in frequency of the intermediate sideband and secondly to movements independent of the substitute carrier. FIG. 6 represents the function block 12 for restoring the attenuated intermediate carrier PIA. It can be designed by any suitable means (microprocessor, digital signal processor, DSP, or other) allowing in a given frequency spectrum to discriminate a particular unknown frequency from a substantially attenuated signal, but of a constant frequency in the short term, this spectrum also comprising the audio information sideband and its modulation products whose components change continuously of frequencies and amplitude according to the information. According to the embodiment shown in FIG. 6, it comprises a band-pass filter 13. The filtered product is applied to an analog / digital converter 14 having a sampling frequency of 100 kHz, for example. The signal from this converter 14 is converted into the frequency domain by means of a Fast Fourier Transform (FFT) circuit, the transformation module being obtained in an extraction circuit 16. It should be noted that the we can be content with module extraction, because to detect frequency peaks (attenuated carriers in the signal) it is not necessary to extract the phase. In the circuit 17, an autocorrelation (XCorr) is carried out on the module and on the signal coming from the analog / digital converter 14. Then, the frequency discrimination is performed by an algorithm which uses as data the modulus of a Fourier transformation. fast (FFT) on the intermediate frequency signal and autocorrelation of this module with the digital form of this signal.

Thus, the result of the autocorrelation operation is applied to a calculation unit 18 implementing the algorithm for extracting the x and x 'peaks of the desired frequency.

The calculation unit 18 produces a signal PIRN representing in numerical value the restored intermediate carrier PIR. In this regard, it should be noted that two x and x 'peaks may be present in the signal due to the fact that the received channel may contain two carriers associated with two BLI and BLS sidebands containing information (FIG. ). This unit 18 then retains the peak x 'at higher frequency or the peak x at lower frequency depending on whether this oscillator 3 is placed on the receiving position of BLI or BLS.

The calculation unit 18 is connected to a digitally controlled oscillator 19 which reproduces the digital value of the frequency of the carrier found, the signal being applied to a digital-to-analog converter 20 which generates the analog wave at the desired intermediate carrier frequency As already indicated, the phase angle is not important in the case of a receiver. of BLU by envelope detection object of the invention. A filter 21 is responsible for eliminating parasitic frequencies. The resulting signal is the restored PIR carrier with which the detection will be performed in the detection circuit 9.

The injection of the restored PIR carrier into the detection circuit 9 of the receiver shown in FIG. 5 makes it possible to avoid, above all, the modification of the frequency difference between the intermediate useful information sideband and the substitution carrier conventionally applied to the signal. detector 9, thereby avoiding type B deformations.

However, certain drifts or frequency errors at the level of remission and / or at the level of the local oscillator 3 may cause a major decentering of the intermediate intermediate band useful vis-à-vis the intermediate frequency filter 7, as has been illustrated by Figures 4A and 4B described above. This can also result in type A deformation of the useful audio signal after detection.

FIG. 7 represents the diagram of a receiver according to the invention equipped with an improvement which, in addition to that described with regard to FIG. 5, makes it possible to remedy these possible decentering defects resulting in type A deformation.

In this case, the receiver further comprises an automatic control loop of the CAF frequency of the attenuated carrier PIA (associated with the information sideband) present at the output of the mixer 2, the receiver being equipped with a local oscillator 3A of voltage controlled type (VCO). This control loop generates as an error signal the result of a comparison between the restored carrier PIR which for this purpose is applied to an analog comparator 22 and a standard signal produced in a standard oscillator 23 whose output is applied to the Another input of the comparator 22. This oscillator 23 produces as the case the theoretical nominal frequency of the intermediate carrier of the BLI or the BLS. The error voltage generated by the analog comparator 22 is applied to the input of VCO, Vx, the oscillator 3A whose frequency will be corrected accordingly to determine with the mixer 2 the intermediate frequencies at its output, which completes the CAF loop. Thus, the residual carrier PIA upstream of the filter 7 and the restored carrier PIR will be corrected at any time to take the frequency value of the oscillator 23, which compensates for the errors and frequency drifts of the received transmission and the transmission. local oscillator 3 of Figures 2 and 5. This results in a permanent automatic refocusing of the sideband signal useful vis-à-vis the bandwidth of the filter 7, and thus avoids as well the type A deformations as those of type B, these being corrected by the function block 12 as in the case of FIG.

FIG. 8 represents the diagram of a receiver designed according to another embodiment of the invention in which the digital processing of the heavily attenuated intermediate carrier PIA is also implemented, but without using it for the detection, in employing a different way from what has been described previously. This embodiment comprises a variant of the function block 12 of FIG. 6, referred to herein as 12A and shown in detail in FIG. 9.

In addition to extracting a signal representing the attenuated intermediate carrier developed from the PIA signal as does the function block 12 of FIGS. 5 and 7, the function block 12A also makes it possible to develop a VCO control signal VCO of the oscillator 3A.

The receiver of FIG. 8 comprises the components 1, 2, 3A, 7, 8, 9, and 23 already described with reference to FIG. 7. The block 12A comprises the function units 13 to 18 of the block 12 of FIG. .

The oscillator 23 serves here to provide a fixed PISubstit standard signal (except switching on the appropriate BLI or BLS band) which allows the detection circuit for SSB 9 to generate the useful audio signal on the terminal 10 by detecting the envelope. using this surrogate carrier. However, and moreover, the frequency of the signal of the oscillator 23 is measured by a counter 24 forming part of the function block 12A, and the resulting numerical value is applied to a digital comparator 25.

This comparator 25 also receives the digital values of the attenuated intermediate carrier PIRN appearing in digital form at the output of the calculation unit 18 and it determines the difference between the two digital values respectively corresponding to the frequency of the oscillator 23 and that of the intermediate attenuated carrier received PIA. A table 26 makes it possible to generate a numerical value corresponding to the result of the comparison made in the comparator 25. This digital value is converted into an analog value by a digital / analog converter 27 which supplies a DC voltage varying according to the difference between the frequency oscillator 23 and that of the intermediate attenuated carrier PIR. This DC voltage is preferably applied to a low pass filter 28 (which may however be optional) and then transmitted as a VCO control signal VCO to the oscillator 3A. Thus, the frequency of the latter will be corrected accordingly to determine with the mixer 2 the intermediate frequencies appearing at the output of the latter, which completes the CAF loop. The frequency of the residual carrier PIA upstream of the filter 7 will therefore be corrected at any moment to take the value of the frequency of the oscillator 23. Compensation is thus obtained for the errors and drifts in the frequency of the transmission received and the local oscillator 3A. This also results in a permanent automatic refocusing of the signal of the useful sideband vis-à-vis the bandwidth of the filter 7, which avoids the deformations of type A and B described. It should be noted that in all the embodiments described above, it is possible to envisage optionally providing a manual clarifier which the user of the receiver can make use of if he wishes, during the operation thereof. , possibly complementing the automatisms provided by the features of the invention.

Claims

A method of receiving a telecommunication whose useful information is contained in a single sideband (BLI, BLS) of a telecommunication channel whose carrier (PHFA) is heavily attenuated in the telecommunication transmitted, which method comprises: generating from the received telecommunication signal an intermediate frequency signal (PIA) by heterodyning with a local mixing signal, variable according to the frequency of the carrier (PHFA) of the telecommunication channel to be received, - filtering said signal intermediate frequency through a bandwidth (BP) corresponding to the sideband containing said information, amplifying the signal from the filtration, locally generating a carrier (PIR; PISubstit) and subjecting the signal from the amplification to an envelope detection for BLU using said locally generated carrier to extract said useful information from said signal from amplification, characterized in that said signal from the heterodyning is subjected to a frequency discrimination to extract a signal of restitution of the carrier (PIR; PIRN) whose frequency will be identical to that of the residue after heterodyning the heavily attenuated carrier of said transmitted telecommunication and using said carrier restitution signal to reduce the deformations that may affect the reception of the useful information band.

2. Method according to claim 1, characterized in that it consists in using said intermediate carrier restitution signal (PIR) to perform said detection.

3. Method according to claim 2, characterized in that it consists in generating a standard signal having a nominal frequency equal to the nominal frequency of the carrier after heterodyning said intermediate frequency signal, comparing said intermediate carrier restitution signal ( PIR) to said locally generated standard signal for generating a comparison signal (Vx) and adjusting the frequency of said local mixing signal according to said comparison signal (Vx).

4. Method according to claim 1, characterized in that it consists in generating a standard signal (PISubstit) having a frequency equal to the nominal frequency of the intermediate carrier (PIA) after heterodyning said intermediate frequency signal, to use said signal stallion like

Carrier for envelope detection, comparing said calibration signal with said carrier restitution signal (PIRN) and adjusting said local mixing signal according to the difference (Vx) found in said comparison.

5. Method according to any one of claims 1 to 4, characterized in that the frequency discrimination is performed by an algorithm which uses as data the module of a Fast Fourier Transform (FFT) on said intermediate frequency signal and autocorrelation of this module with the digital form of this signal.

Receiver for the implementation of the method as defined in any one of claims 1 to 5, adapted to receive a telecommunication whose useful information is contained in a single sideband (BLI, BLS) of a channel telecommunication carrier whose carrier (PHAF) is greatly attenuated in the telecommunication transmitted, this receiver comprising: - an antenna (1) intended to pick up said telecommunication, an adjustable local oscillator (3; 3A) for generating a local mixing signal, variable according to the frequency of the telecommunication channel to receive, a mixer (2) for generating an intermediate frequency signal by heterodyning with said local signal, an intermediate frequency filter (7) having a bandwidth corresponding to the sideband of the telecommunication containing said information, an amplifier (8) of the signal from said filter (7) to provide an amplified signal, means (12; 23) for locally generating a carrier, envelope detection means (9) for BLU for extracting said useful information from said amplified signal using the locally generated carrier, characterized in that it further comprises a function block (12; 12A) connected on the one hand to discriminate in said signal derived from the heterodynage (PIR) applied to said intermediate frequency filter (7), a carrier restitution signal (PIR) whose frequency is identical to that of the residue after heterodyning of the heavily attenuated carrier of said transmitted telecommunication and secondly to use said carrier restitution signal to reduce deformations that may affect the reception of said useful information band.

The receiver according to claim 6, characterized in that the output of said function block (12) is connected to said detection circuit for SSB (9) for using said intermediate carrier restitution signal as a local carrier for the detection.

8. Receiver according to claim 7, characterized in that said local oscillator (3A) is an oscillator equipped with a frequency adjustment by a voltage (VCO) and the receiver further comprises a standard oscillator (23) for generating a standard signal having the nominal theoretical frequency of said intermediate carrier and an analog comparator (22), one of whose inputs is connected to said standard oscillator (23) and whose other input is connected to said function block (12) and whose the output is connected to the control input (Vx) of said local oscillator (3A) in order to control the frequency as a function of the result of the comparison made by said comparator (22) between said standard signal and said feedback signal of the carrier (PIR).

9. Receiver according to claim 6, characterized in that said local oscillator (3A) is an oscillator equipped with a frequency adjustment by a voltage (VCO) and said receiver further comprises a standard oscillator (23) for generating a standard signal having the nominal theoretical frequency of said intermediate carrier, the output of said standard oscillator being connected on the one hand to said detection circuit for SSB and on the other hand to an input of said function block (12A), and in that said function block (12A) comprises means (25 to 28) for comparing a digital value representing the frequency of said standard signal with a digital value representing the frequency of said signal of intermediate carrier (PIRN) and to apply the result of the comparison in analog form to the control input (Vx) of said local oscillator (3A).

Receiver according to any one of claims 6 to 9, characterized in that said function block (12; 12A) of calculating means (18) which by means of an algorithm performs said frequency discrimination, said computing means being connected to means (15) for performing a fast Fourier transform (FFT) of said intermediate frequency signal, means (16) for performing the extraction of the module after this transformation and means (17) for performing the autocorrelation of this module with the digital form of this intermediate frequency signal.