METHOD FOR DETECTING AND ATTENUATING THE IMPACT OF INTERFERENCE IN A SIGNAL OF A RADIO RECEIVER WITH MULTIPLE TUNERS

Abstract

A method for detecting and attenuating the impact of interference in a signal of a radio receiver with multiple tuners. The method includes providing a first input signal RF.sub.1 to a first tuner T.sub.1; simultaneously providing a second input signal RF.sub.2 to a second tuner T.sub.2; simultaneously producing a first intermediate high injection signal IFH.sub.1, by the first tuner T.sub.1, using the first input signal RF.sub.1 filtered on a first frequency f.sub.E, and a first intermediate low injection signal IFB.sub.2, by the second tuner T.sub.2, using the second input signal RF.sub.2 filtered on the first frequency f.sub.E; comparing the first intermediate high injection signal IFH.sub.1 and the first intermediate low injection signal IFB.sub.2; selecting one out of the first intermediate high injection signal IFH.sub.1 and the first intermediate low injection signal IFB.sub.2 to be decoded by the radio receiver.

Claims

1. A method for detecting and attenuating the impact of interference in a signal of a radio receiver with multiple tuners, the method comprising: a. providing a first input signal RF.sub.1 to a first tuner T.sub.1, b. providing a second input signal RF.sub.2 to a second tuner T.sub.2, simultaneously with step a, c. simultaneously producing a first intermediate high injection signal IFH.sub.1, by the first tuner T.sub.1, using the first input signal RF.sub.1 filtered on a first frequency f.sub.E, and a first intermediate low injection signal IFB.sub.2, by the second tuner T.sub.2, using the second input signal RF.sub.2 filtered on the first frequency f.sub.E, d. comparing the first intermediate high injection signal IFH.sub.1 and the first intermediate low injection signal IFB.sub.2, and e. selected one out of the first intermediate high injection signal IFH.sub.1 and the first intermediate low injection signal IFB.sub.2 having the best quality for decoding by the radio receiver.

2. The method as claimed in claim 1, wherein the first input signal RF.sub.1 and the second input signal RF.sub.2 are acquired by a single antenna A.sub.1.

3. The method as claimed in claim 1, wherein the first input signal RF.sub.1 is acquired by a first antenna A.sub.1 and the second input signal RF.sub.2 are acquired by a second antenna A.sub.2, the method further comprising: f. simultaneously producing a second intermediate low injection signal IFB.sub.1, by the first tuner T.sub.1, using the first input signal RF.sub.1 filtered on the first frequency f.sub.E, and a second intermediate high injection signal IFH.sub.2, by the second tuner T.sub.2, using the second input signal RF.sub.2 filtered on the first frequency f.sub.E, g. comparing the second intermediate low injection signal IFB.sub.1 and the second intermediate high injection signal IFH.sub.2, steps f and g being executed between steps d and e, step e consisting in selecting one out of the first intermediate high injection signal IFH.sub.1, the first intermediate low injection signal IFB.sub.2, the second intermediate low injection signal IFB.sub.1 and the second intermediate high injection signal IFH.sub.2 having the best quality for decoding by the radio receiver (10).

4. The method as claimed in claim 3, wherein step c is executed at a first instant t1, step f is executed at a second instant t2, the first instant t1 and the second instant t2 being spaced apart by a time interval Δt during which the first input signal RF.sub.1 and the input signal RF.sub.2 are invariant, the time interval preferably being equal to 10 ms.

5. The method as claimed in claim 1, wherein step c comprises a subsidiary step consisting in digitizing the first intermediate high injection signal IFH.sub.1 and the first intermediate low injection signal IFB.sub.2, and if necessary step f comprising a subsidiary step consisting in digitizing the second intermediate low injection signal IFB.sub.1 and the second intermediate high injection signal IFH.sub.2.

6. The method as claimed in claim 1, wherein step d comprises the following substeps: i. determining a first difference signal between a power spectral density of the first intermediate high injection signal IFH.sub.1 and a power spectral density of the first intermediate low injection signal IFB.sub.2, ii. analyzing the first difference signal, step g also comprising, if necessary, the following substeps: i. determining a second difference signal between a power spectral density of the second intermediate low injection signal IFB.sub.1 and a power spectral density of the second intermediate high injection signal IFH.sub.2, ii. analyzing the second difference signal.

7. The method as claimed in claim 6, wherein each substep ii comprises evaluating the first difference signal, and if necessary the second difference signal, with respect to an interference threshold.

8. The method as claimed in claim 6, wherein each substep ii comprises evaluating the sign of the first difference signal, and if necessary that of the second difference signal.

9. A motor vehicle radio receiver for implementing the method as claimed in claim 1, the radio receiver having multiple tuners T.sub.1, T.sub.2, the radio receiver comprising at least a first antenna A.sub.1 and a second antenna A.sub.2 and a digital central part for signal processing.

10. The method as claimed in claim 7, wherein each substep ii comprises evaluating the sign of the first difference signal, and if necessary that of the second difference signal.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Other features, details and advantages will become apparent from reading the following detailed description and from analyzing the appended drawings, in which:

[0034] FIG. 1 shows schematically a radio receiver for a vehicle,

[0035] FIG. 2 shows schematically and in greater detail the radio receiver of FIG. 1,

[0036] FIG. 3 shows a flow chart of a first example of a method for detecting and attenuating interference in the signal to be decoded by the radio receiver of FIGS. 1 and 2,

[0037] FIG. 4 shows schematically the first example of a method of FIG. 3 in a first case,

[0038] FIG. 5 shows schematically the first example of a method of FIG. 3 in a second case,

[0039] FIG. 6 shows a flow chart of a second example of a method for detecting and attenuating interference in the signal to be decoded by the radio receiver of FIGS. 1 and 2,

[0040] FIG. 7 shows schematically the second example of a method of FIG. 6 in a first case,

[0041] FIG. 8 shows schematically the second example of a method of FIG. 6 in a second case,

[0042] FIG. 9A shows the operation of a mixer in the case of a high injection,

[0043] FIG. 9B shows the operation of a mixer in the case of a low injection.

DESCRIPTION OF THE EMBODIMENTS

[0044] The drawings and descriptions below essentially contain elements of definite character. Consequently they can be used not only to clarify the understanding of the present disclosure, but also to contribute to its definition if necessary.

[0045] In the various figures, the same references denote identical or similar elements. In the interests of brevity, only those elements that are useful for the understanding of the embodiment described are shown in the figures and described in detail below. Only the differences between the examples presented are described in detail.

[0046] FIG. 1 shows schematically a radio receiver 10 for a vehicle notably a motor vehicle. The radio receiver 10 has multiple tuners, in the sense that it comprises at least two tuners. According to the example of FIG. 1, the radio receiver 10 comprises a first tuner T.sub.1 connected to a first antenna A.sub.1. Similarly, the radio receiver 10 comprises a second tuner T.sub.2 connected to a second antenna A.sub.2. According to another example described below, the first tuner T.sub.1 and the second tuner T.sub.2 may be connected to the same antenna. Optionally, a third tuner T.sub.3 and a fourth tuner T.sub.4 may be connected, respectively, to a third antenna A.sub.3 and a fourth antenna A.sub.4.

[0047] A tuner T is described below, this description being applicable to each tuner T.sub.1, T.sub.2 of the radio receiver 10 of the description. The tuner T is connected to an antenna A. The tuner T receives an input signal RF captured by the antenna A. The input signal RF comprises a large number of frequencies, each carrying information to be decoded. The tuner T may be used, in the first place, to filter the input signal RF at a selected input frequency f.sub.E, the input frequency f.sub.E of the input signal RF notably carrying information to be decoded. In the rest of the description, the input frequency f.sub.E is taken to mean the frequency at which a user of the radio receiver 10 wishes to decode the information carried by the input frequency f.sub.E of the input signal. The input frequency f.sub.E may, notably, be between 88 MHz and 108 MHz, for example.

[0048] The tuner T also comprises a mixer. The mixer combines the filtered input signal RF with a local oscillator signal LO, to produce an intermediate signal IF, an intermediate frequency f.sub.IF of which is shifted with respect to the input frequency f.sub.E. In particular, the intermediate frequency f.sub.IF of the intermediate signal IF is equal to the absolute value of the difference between the input frequency f.sub.E of the input signal RF and a frequency f.sub.LO of the local oscillator signal LO.

[0049] The frequency f.sub.LO of the local oscillator signal LO of the mixer is variable. The frequency f.sub.LO of the local oscillator signal LO may thus be controlled so as to obtain the desired intermediate frequency f.sub.IF of the intermediate signal IF. There are two distinct frequencies f.sub.LO that may be used to obtain the same desired intermediate frequency f.sub.IF of the intermediate signal IF.

[0050] In a first case, shown in FIG. 9A, the frequency f.sub.LO of the local oscillator signal LO is higher than the input frequency f.sub.E of the input signal RF. In the first case, the intermediate signal IF that is obtained is called the intermediate high injection signal IFH. In particular, the intermediate frequency f.sub.IFH of the intermediate high injection signal IFH is equal to the difference between the frequency f.sub.LO of the local oscillator signal LO and the input frequency f.sub.E of the input signal RF.

[0051] In a second case, shown in FIG. 9B, the frequency f.sub.LO of the local oscillator signal LO is lower than the input frequency f.sub.E of the input signal RF. In the second case, the intermediate signal IF that is obtained is called the intermediate low injection signal IFB. The intermediate frequency f.sub.IFB of the intermediate signal IF is equal to the difference between the input frequency f.sub.E of the input signal RF and the frequency f.sub.LO of the local oscillator signal LO.

[0052] In the following text, unless specified otherwise, “intermediate signal IF” is taken to mean an intermediate injection signal that may equally well be high or low.

[0053] Additionally, unless indicated otherwise, the tuners T.sub.1, T.sub.2 are in this case parameterized so as to produce, respectively, first and second intermediate signals IF.sub.1 and IF.sub.2, each having an intermediate frequency f.sub.IF that is close to, or even identical with, the other. It is also possible to fix the intermediate frequency f.sub.IF of each intermediate signal IF.sub.1, IF.sub.2 at a standard value, for example 10.7 MHz. The processing and/or comparison of the intermediate signals IF.sub.1, IF.sub.2 may, notably, be facilitated by this arrangement.

[0054] With reference to FIG. 1, the radio receiver 10 further comprises a digital central part 12 with a logic control unit (digital core), and an analog downstream part with an amplifier and loudspeakers 16. An analog to digital converter 14 separates the digital central part from the tuners T.sub.1, T.sub.2. Similarly, a digital to analog converter 15 separates the digital central part 12 from the analog downstream part. Additionally, the audio system comprises a user interface with a display screen 18 (‘Display’) and a touch-sensitive surface and/or physical buttons (not shown), enabling the user to choose the input frequency f.sub.E.

[0055] FIG. 2 shows schematically, in greater detail, the digital central part 12 of the radio receiver 10 for implementing a method for detecting and attenuating interference, as described in detail below.

[0056] As shown in FIG. 2, the digital central part 12 comprises, notably, a first block 19 for transposing the first and second intermediate signals IF.sub.1, IF.sub.2, obtained from the first and second tuners T.sub.1, T.sub.2 respectively, to baseband. Each intermediate signal IF.sub.1, IF.sub.2 in baseband may then be stored in a data buffer of the first block 19. Using these stored data, a Fourier transform analysis is then performed, to produce at the output of the first block 19 a power spectral density curve representative of the first intermediate signal IF.sub.1 and a power spectral density curve representative of the second intermediate signal IF.sub.2.

[0057] The digital central part 12 comprises at least a first comparator block C.sub.1. The digital central part 12 may also comprise a second comparator block C.sub.2. Each comparator block C.sub.1, C.sub.2 determines a first difference signal and a second difference signal respectively. Each difference signal corresponds to a difference between the power spectral density curve representative of the first intermediate signal IF.sub.1 and the power spectral density curve representative of the second intermediate signal IF.sub.2.

[0058] The digital central part 12 comprises a selection block S, enabling the difference signals calculated by the comparator blocks C.sub.1, C.sub.2 to be analyzed subsequently. Notably, the selection block S may be used to evaluate each difference signal with respect to a predefined threshold. The selection block S may also be used to evaluate the sign of each difference signal. According to the results of the analysis of a difference signal between the intermediate signal IF.sub.1 and the intermediate signal IF.sub.2, the selection block S can then select one out of the intermediate signal IF.sub.1 and the intermediate signal IF.sub.2 to be demodulated by a demodulation block D. It is known to obtain a demodulated audio signal using such a demodulation block D. Accordingly, the demodulation block D will not be described in greater detail here.

[0059] Some or all of the operations of transposition, storage, Fourier transform, comparison, analysis, selection and demodulation may be carried out by a dedicated circuit of the DSP (“digital signal processor”) type.

[0060] FIG. 3 shows a flow chart of a first example of a method for detecting and attenuating interference in the signal to be decoded by the radio receiver 10 as described above. The first example of a method in a first case is described below in greater detail with reference to FIG. 4.

[0061] A first step 110 of the first example of a method consists in acquiring electromagnetic radio communication waves using an antenna A.sub.1. A first input signal RF.sub.1 is thus transmitted to the first tuner T.sub.1. Similarly, a second input signal RF.sub.2 is transmitted to the second tuner T.sub.2. For this purpose, the first tuner T.sub.1 and the second tuner T.sub.2 are each connected to the antenna A.sub.1. The first signal RF.sub.1 is therefore identical to the second signal RF.sub.2. Here and in the following text, “identical” is taken to mean that the first signal RF.sub.1 and the second signal RF.sub.2 have the same frequency spectrum, and differ only in a residual noise intrinsic to the components of the radio receiver 10.

[0062] In a second step 120, each input signal RF.sub.1, RF.sub.2 is initially filtered by the tuners T.sub.1, T.sub.2 at the same input frequency f.sub.E. The tuner T.sub.1 then produces a first intermediate high injection signal IFH.sub.1 from the first filtered input signal RF.sub.1. Simultaneously, the tuner T.sub.2 produces a first intermediate low injection signal IFB.sub.2 from the second filtered input signal RF.sub.2. The first intermediate high injection signal IFH.sub.1 and the first intermediate low injection signal IFB.sub.2 here have the same intermediate frequency f.sub.IF. It should also be noted that the input frequency f.sub.E of the first input signal RF.sub.1 carries the same information as the input frequency f.sub.E of the second input signal RF.sub.2. The first intermediate high injection signal IFH.sub.1 and the first intermediate low injection signal IFB.sub.2 therefore each carry the same information obtained from the input signals RF.sub.1 and RF.sub.2.

[0063] As shown in FIG. 4, the tuner T.sub.1 receives internal electromagnetic transmissions 20. The internal electromagnetic transmissions 20 are transmitted by components inside the radio receiver 10. The internal electromagnetic transmissions 20 may, for example, be harmonics originating from a mixer of the second tuner T.sub.2. The internal electromagnetic transmissions 20 interfere with the production of the first intermediate high injection signal IFH.sub.1 by the first tuner T.sub.1. For example, the internal electromagnetic transmissions 20 have a frequency close to the frequency f.sub.IF of the first intermediate high injection signal IFH.sub.1. Interference is therefore superimposed on the first intermediate high injection signal IFH.sub.1. In another case, the internal electromagnetic transmissions 20 may have a frequency close to the frequency f.sub.LO of the local oscillator signal LO of the first tuner T.sub.1. The input signal RF.sub.1 is then combined with the local oscillator signal LO that contains interference, resulting in a first intermediate high injection signal IFH.sub.1 that also contains interference. The interference has a parasitic effect on the information carried by the first intermediate high injection signal IFH.sub.1.

[0064] However, the first intermediate low injection signal IFB.sub.2 is free of any interference in this case. The information carried by the first intermediate low injection signal IFB.sub.2 is therefore unaffected.

[0065] The first intermediate high injection signal IFH.sub.1 and the first intermediate low injection signal IFB.sub.2 are then converted to digital signals in a third step 130.

[0066] A fourth step 140, executed by the first block 19 of the digital central part 12, then consists in transposing the first intermediate high injection signal IFH.sub.1 and the first intermediate low injection signal IFB.sub.2 to baseband. A first power spectral density curve 22 representative of the first intermediate high injection signal IFH.sub.1 and a second power spectral density curve 24 representative of the first intermediate low injection signal IFB.sub.2 are then formed.

[0067] The first curve 22 differs from the second curve 24 in that the interference creates a power excess 26 in a portion of the spectrum associated with the first intermediate high injection signal IFH.sub.1. Evidently, the first curve 22 representative of the first intermediate high injection signal IFH.sub.1 may have a plurality of power excesses 26, each caused by interference superimposed on the first intermediate high injection signal IFH.sub.1. On the other hand, the first curve 22 and the second curve 24 are identical over the frequency ranges that are not affected by interference. It should be noted that, in the absence of interference, the first curve 22 and the second curve 24 are identical over the whole frequency domain. Here again, “identical” means that the first and second curves 22, 24 differ from each other only in the residual noise affecting the first intermediate high injection signal IFH.sub.1 and/or the first intermediate low injection signal IFB.sub.2.

[0068] The first intermediate high injection signal IFH.sub.1 and the first intermediate low injection signal IFB.sub.2 are then compared, using the first comparator block C.sub.1, in a fifth step 150. Notably, the first comparator block C.sub.1, establishes a first difference signal 28. The first difference signal 28 is due to the difference between the first curve 22 and the second curve 24.

[0069] The first difference signal 28 obtained by the first comparator block C.sub.1 watch thus exhibits a signal that is close to, or even equal to, zero over the frequency ranges in which the first intermediate high injection signal IFH.sub.1 is not affected by the interference. On the other hand, the first difference signal 28 comprises a power peak 30 corresponding to the power excess 26 associated with the interference affecting the first intermediate high injection signal IFH.sub.1. Here, the power peak 30 is positive. As explained below, the power peak 30 may also be negative in other cases.

[0070] In a sixth step 160, the selection block S determines the presence of the power peak 30 by comparing the difference signal 28 with a predefined threshold. The threshold may be used, notably, to differentiate the power peak 30 from the frequency ranges in which the first difference signal 28 is close to zero but is not zero, this being due to a residual noise affecting the first intermediate high injection signal IFH.sub.1 and/or the first intermediate low injection signal IFB.sub.2.

[0071] The selection block S also evaluates the sign of the power peak 30 in the sixth step 160. The interference is superimposed on the first intermediate high injection signal IFH.sub.1. The interference causes only a power excess 26 at its transmission frequency on the first power spectral density curve 22 of the first intermediate high injection signal IFH.sub.1. Thus the interference superimposed on the first intermediate high injection signal IFH.sub.1 here causes only a positive power peak 30 in the first difference signal 28. Similarly, as described below, interference superimposed on the first intermediate low injection signal IFB.sub.2, conversely, causes only a negative power peak 30 in the first difference signal 28. However, this depends on the order in which the difference between the first intermediate high injection signal IFH.sub.1 and the first intermediate low injection signal IFB.sub.2 is established.

[0072] Consequently, the evaluation of the sign of the power peak 30 enables the selection block S to determine which of the first intermediate high injection signal IFH.sub.1 and the first intermediate low injection signal IFB.sub.2 is affected by interference. In the case of FIG. 4, the selection block S determines that the first intermediate high injection signal IFH.sub.1 is affected by interference.

[0073] Using this information, the selection block S advantageously selects the one out of the first intermediate high injection signal IFH.sub.1 and the first intermediate low injection signal IFB.sub.2 that has less interference before being decoded. Thus the audio signal obtained from the selected intermediate signal is not subjected to parasitic interference. In the case of FIG. 4, the selection block S selects the first intermediate low injection signal IFB.sub.2 for decoding. The first intermediate high injection signal IFH.sub.1 may, however, still be used for functions of lower priority, such as an alternative frequency quality test, for example.

[0074] The first intermediate low injection signal IFB.sub.2 is thus demodulated by the demodulation block D in a seventh step 170. The demodulated signal is converted to an analog signal in an eighth step 180, so that it can be sent to the amplifier and the loudspeakers 16.

[0075] FIG. 5 shows schematically the first example of a method in a second case. The second case differs from the first case essentially in that it is the second tuner T.sub.2 that receives internal electromagnetic transmissions 20. Interference is then superimposed on the first intermediate low injection signal IFB.sub.2 obtained in the second step 120.

[0076] The second power spectral density curve 24 representative of the first intermediate low injection signal IFB.sub.2, plotted in the fourth step 140, thus shows a power excess 26 in a portion of the spectrum associated with the first intermediate low injection signal IFB.sub.2. Here, the first curve 22 is free of any interference.

[0077] The first difference signal 28 obtained in the fifth step 150 thus has a negative power peak 30. In the sixth step 160, the selection block S determines that the first intermediate low injection signal IFB.sub.2 is affected by interference, and therefore selects the first intermediate high injection signal IFH.sub.1 to be demodulated in the seventh step 170.

[0078] FIGS. 6 to 8 relate to a second example of a method for detecting and attenuating interference affecting the signal to be decoded by the radio receiver 10 as described above. FIG. 6 shows a flow chart of the second example of a method. Firstly, with reference to FIG. 7, a first case of the second example of a method is described below.

[0079] As shown in FIG. 7, the first tuner T.sub.1 is connected to a first antenna A.sub.1. Similarly, the second tuner T.sub.2 is connected to a second antenna A.sub.2.

[0080] The second example of a method comprises a variant first step 110′. The variant first step 110′ consists in the simultaneous acquisition of a first input signal RF.sub.1 via a first antenna A.sub.1 and a second input signal RF.sub.2 via a second antenna A.sub.2. The first input signal RF.sub.1 is transmitted to the first tuner T.sub.1. Similarly, the second input signal RF.sub.2 is transmitted to the second tuner T.sub.2. The first input signal RF.sub.1 and the second input signal RF.sub.2 are acquired simultaneously, and therefore each carry the same information.

[0081] In the first case shown in FIG. 7, the second antenna A.sub.2 receives external electromagnetic transmissions 31 transmitted by other components of the vehicle. Here, the external electromagnetic transmissions 31 have a frequency close to the input frequency f.sub.E. The acquisition of the second input signal RF.sub.2 by the second antenna A.sub.2 is then affected by interference. Interference is superimposed on the second input signal RF.sub.2, notably in the vicinity of the input frequency f.sub.E. Interference then has a parasitic effect on the information carried by the input frequency f.sub.E of the second input signal RF.sub.2.

[0082] On the other hand, the first antenna A.sub.1 does not receive any external electromagnetic transmissions. This may be due, notably, to the fact that the first antenna A.sub.1 and the second antenna A.sub.2 are located in different positions on the vehicle. The signal RF.sub.1 is therefore free of any interference. The information carried by the input frequency f.sub.E of the first input signal RF.sub.1 is therefore unaffected.

[0083] The second example of a method comprises the second to the fifth steps 120, 130, 140, 150 as described above for the first example of a method. Here, the second step 120 is executed at a first instant t1.

[0084] As shown in FIG. 7, the second curve 24 has a power excess 26 in a portion of the spectrum associated with the first intermediate low injection signal IFB.sub.2. This power excess 26 corresponds to the interference superimposed on the second input signal RF.sub.2 when it is acquired by the second antenna A.sub.2. The first difference signal 28 thus exhibits a negative power peak 30.

[0085] The second example of a method further comprises a variant second step 120′. The second step 120′ is executed at a second instant t2. The first instant t1 and the second instant t2 are separated by a time interval Δt. In the variant second step 120′, each tuner T.sub.1, T.sub.2 equally receives the first and second input signals RF.sub.1, RF.sub.2 respectively. Thus the time interval Δt is such that each input signal RF.sub.1, RF.sub.2 is invariant over the time interval Δt. In other words, the frequency spectrum of each signal RF.sub.1, RF.sub.2 does not vary between the first instant t1 and the second instant t2. For this purpose, the time interval Δt is less than 20 ms, preferably being equal to 10 ms.

[0086] In the variant second step 120′, each input signal RF.sub.1, RF.sub.2 is then filtered by the respective tuners T.sub.1, T.sub.2 at the same input frequency f.sub.E as in the second step 120. The variant second step 120′ is distinguished from the second step 120 in that a second intermediate low injection signal IFB.sub.1 is obtained from the first input signal RF.sub.1, and in that a second intermediate high injection signal IFH.sub.2 is obtained from the second input signal RF.sub.2.

[0087] The second example of a method then comprises successive variant third, fourth and fifth steps, 130′, 140′ and 150′, following the variant second step 120′. The variant third, fourth and fifth steps 130′, 140′ and 150′ respectively include all the operations of the third, fourth and fifth steps 130, 140 and 150 as described above, but applied to the second intermediate low injection signal IFB.sub.1 and to the second intermediate high injection signal IFH.sub.2.

[0088] FIG. 7 shows a third power spectral density curve 32 representative of the second intermediate low injection signal IFB.sub.1 and a fourth power spectral density curve 34 representative of the first intermediate high injection signal IFH.sub.2, each being produced in the variant fourth step 140′.

[0089] The fourth curve 34 exhibits a power excess 26 on a portion of the spectrum associated with the second intermediate high injection signal IFH.sub.2, this power excess 26 corresponding to the interference superimposed on the second input signal RF.sub.2 when it is acquired by the second antenna A.sub.2.

[0090] However, the third curve 32, representative of the second intermediate low injection signal IFB.sub.1, is free of any interference in this case.

[0091] The second intermediate low injection signal IFB.sub.1 and the second intermediate high injection signal IFH.sub.2 are then compared, using a second comparator block C.sub.2, in the variant fifth step 150′. In an alternative, the second intermediate low injection signal IFB.sub.1 and the second intermediate high injection signal IFH.sub.2 may be compared using the first comparator block C.sub.1. In this alternative, the digital central part 12 may comprise only the first comparator block C.sub.1.

[0092] A second difference signal 36 obtained in the variant fifth step 150′, using the second intermediate low injection signal IFB.sub.1 and the second intermediate high injection signal IFH.sub.2, therefore exhibits a negative power peak 30 corresponding to the power excess 26 present in the fourth curve 34.

[0093] In a variant sixth step 160′, the selection block S determines that interference is superimposed on the first intermediate low injection signal IFB.sub.2 and on the second intermediate high injection signal IFH.sub.2. Here, the selection block S is also capable of recognizing that the first intermediate low injection signal IFB.sub.2 and the second intermediate high injection signal IFH.sub.2 are affected in the same way by the interference. This is because the negative power peak 30 of the first difference signal 28 is located at the same frequency as the negative power peak 30 of the second difference signal 36. Thus it may be deduced from this that the interference is due to external electromagnetic transmissions 20 affecting the acquisition of the input signal RF.sub.2.

[0094] Using this information, the selection block S selects one of the first intermediate high injection signal IFH.sub.1 and the second intermediate low injection signal IFB.sub.1, both obtained from the first tuner T.sub.1, to be demodulated.

[0095] The second example of a method then comprises the seventh and eighth steps 170 and 180 as described above for the first example of a method.

[0096] FIG. 8 shows a second case of the second example of a method. The second case of the second example of a method is distinguished from the first case of the second example of a method in that the first tuner T.sub.1 and the second tuner T.sub.2 are also each affected by internal electromagnetic transmissions 20.

[0097] In particular, the internal electromagnetic transmissions 20 interfere with the production of the first intermediate high injection signal IFH.sub.1 by the first tuner T.sub.1, in such a way that the interference is superimposed on the first intermediate high injection signal IFH.sub.1. The first power spectral density curve 22 representative of the first intermediate high injection signal IFH.sub.1 therefore exhibits a power excess 26 due to the internal electromagnetic transmissions 20 affecting the first tuner T.sub.1. However, the third curve 32, representative of the second intermediate low injection signal IFB.sub.1, also obtained from the first tuner T.sub.1, is free of any interference.

[0098] Similarly, the internal electromagnetic transmissions 20 interfere with the production of the second intermediate high injection signal IFH.sub.2 by the second tuner T.sub.2, in such a way that the interference is superimposed on the second intermediate high injection signal IFH.sub.2. The fourth power spectral density curve 34 representative of the second intermediate high injection signal IFH.sub.2 therefore exhibits a first power excess 26a due to the internal electromagnetic transmissions 20 affecting the second tuner T.sub.2.

[0099] The fourth curve 34 also exhibits a second power excess 26b associated with interference due to external electromagnetic transmissions 31 affecting the second input signal RF.sub.2. Similarly, the second curve 24 also exhibits a power excess 26b associated with interference due to the external electromagnetic transmissions 31.

[0100] Therefore, the first difference signal 28 comprises a positive power peak 30 associated with the power excess 26 of the first curve 22 and a negative power peak 30 associated with the power excess 26b of the second curve 24. Similarly, the second difference signal 36 comprises two negative power peaks 30 associated with the first and second power excesses 26a, 26b of the fourth curve 34.

[0101] The selection block S determines, using the first difference signal 28, that interference is superimposed on the first intermediate high injection signal IFH.sub.1. The selection block S also determines that the second intermediate low injection signal IFB.sub.1 is free of any interference, since the second difference signal 36 does not comprise a positive power peak 30. Therefore, it may be deduced from the above that the tuner T.sub.1 is affected by internal electromagnetic transmissions 20.

[0102] The first difference signal 28 and the second difference signal 36 then each have a negative power peak 30 at the same frequency. The selection block S therefore determines that the first intermediate low injection signal IFB.sub.2 and the second intermediate high injection signal IFH.sub.2 comprise interference originating from external electromagnetic transmissions 31 affecting the second input signal RF.sub.2. The selection block S also determines that the second tuner T.sub.2 is receiving internal electromagnetic transmissions 20, since the second difference signal 36 comprises a negative power peak 30 that has no equivalent in the first difference signal 28.

[0103] According to these results, the selection block S selects the second intermediate low injection signal IFB.sub.1 for demodulation.

[0104] The first and second methods are not limited to the cases described above, and may be applied in numerous cases.

[0105] Furthermore, the first example of a method and/or the second example of a method may each be implemented during the use of the radio receiver 10 by a user. Notably, the audio stream emitted by the radio receiver is not affected by the implementation of any one of the first and the second examples of a method.

[0106] the first example of a method and/or the second example of a method may each be implemented repeatedly during the use of the radio receiver 10. For example, the first example of a method and/or the second example of a method may be implemented with a test recurrence of 1 s. Preferably, the first example of a method and/or the second example of a method are implemented when a user selects a new input frequency f.sub.E. This limits the computation load on the digital central part 12.