SE420881B - SET AND RECEIVER TO REDUCE THE INTERFER BETWEEN ADDITIONAL CHANNELS WHEN RECEIVING AN AMPLIED MOLDED SIGNAL - Google Patents

Description

7801100--4- or automatically, and narrowband filters for tone or medium frequency, set by hand to sharply distinguish interference. Compare eg pp. 517, 518,543 and 544 in the publication Radio Receiver Design by K ~ R.Sturley, Second Edition 1953, John Wiley & Sons, Inc., New York.

Several system types have also been developed for automatic change in the selectivity of the receiver due to interference.

The selectivity can be changed symmetrically or asymmetrically. Dy- similar systems are discussed by Sturley on pages 543 and 544 of the above and publication. The variation in selectivity occurs at intermediate frequency in a sensing coupling.

The invention is based on the task of developing inexpensive automatic means of reducing interference while maintaining comparatively good frequency response. The invention is further based on the invention. poison to develop an interference reduction procedure in adjacent channels, which is particularly suitable for stereo reception of amplitude modulated signals. The invention is also based on the above said personal selectivity in order to further distinguish between interference and enables persons listening to amplitude modulators to monophonic signals and stereo signals, can benefit from its selectivity. _ g The invention can be applied in receiving amplitude modulation the waves and is especially suitable for receiving certain types of amplitude modulated stereo waves. The invention can, for example, be used to reduce interference in adjacent channels when receiving amplitude stereo modulated waves with independent sidebands by: (a) measuring the level of the received interference in the upper side ~ the band stereo channel, which is caused by the interfering channel closest to the upper sideband of the desired signal, (b) measuring the level of interference received in the lower side the band stereo channel, which is caused by the interfering channel adjacent to the lower sideband of the desired signal ochi (C) automatic reduction of the tone frequency band in the stereo channel, i which the greater level of interference occurs, depending on whether the measurement according to Ca) or (b) gives the greatest result when the level for the more powerful interference level exceeds a predetermined one level value. IN In the practice of the invention, it is in many cases desirable to attenuate both the adjacent channel above and below it desired channel with a larger factor than when the plant works without 7801100-4 noticeable interference point. However, it is desirable to use the attenuation of the adjacent channel, in which the larger interference the purification level occurs.

The invention can also be used to enhance a monophonic reception facility performance by enabling the listener uses its selectivity. For receivers with monophonic double-sided band signals are a procedure for improving them performance with respect to interference in adjacent channels through isolation and demodulation of both the upper and lower sidebands in the desired signal and feeding the resulting tone frequency signal the connection to couplings for driving separate converters. The converters can be speakers that can be positioned in the same way as stereo speakers. speakers, dwrs with a spacing of about 1.2-1.8 m. It is also possible to apply the invention by using stereo hearing aids phones such as converters.

There are several paths for isolating and demodulating them the upper and lower sideband channels, among other things through the use of phase shooting and filtering, which techniques are well known. You can do this use the whole carrier or reduced carrier with double sidebands or suppressed carriers, ie complete carriers or waves at which the carrier level is less than the combined peak amplitude of the sidebands.

When the invention is applied to monophonic systems, it is also possible to use means for measuring the level of interference in the channels adjacent to the upper and lower sideband components of the desired and the reduction of the tone frequency band in the channel where it greater level of interference occurs. A listener will therefore not only be able to enjoy the enhanced interference reduction effect due to the selection capacity, but will also be take away the improved selectivity of the plant.

The invention is particularly applicable to receivers for ste- rheophonic signals with independent sidebands, where the stereo-related the information appears in the form of modulation of the upper and lower sideband. In this case, the carrier can be amplitude modulated with information mation, which relates to the stereo sum (left + right), and simultaneously phase modulated with the information relating to stereo differences (left-right). Such a stereo scale is described in detail, e.g. in U.S. Patent Nos. 3,218,393 and 3,908,090. Recipients of such stereo signals may be designed to particularly emphasize the the choice by imparting the phase shifting and sideband separating the coupling special properties, this coupling 7801100-4 Normally would work at intermediate frequency and be fed from a clutch of superheterodyne type. The phase shift and separation coupling would, in contrast to a normal stereo receiver, achieve noticeable separation of interference signal components into adjacent channels, whose frequency exceeds 5 kHz which is normally the acceptable high frequency frequency range for stereo-separated components. By connecting the time on this connection to organs_for separate reinforcement of the frequency outputs from the sideband separation coupling is possible to cause the interference components of one sideband to caused to fall on one of the stereo speakers, while the interference in the channel adjacent to the second sideband would fall at it the second stereo speaker. The desired stereo components would generate spread between the two speakers, as is normal for stereo impression. 1 In both stereophonic and monophonic reception, the ringing of the tone frequency band only occurs when the worst interference in a sideband channel has sufficient amplitude to give rise to eavesdropping problems. If the energy level of the interference is less than one on the other hand, it is generally a percentage of the desired sideband energy level unnecessary to reduce the tone frequency band. The bandwidth of the channel, i which a stronger level of interference occurs, is reduced in a to about one third of the total bandwidth of the channel. At e.g. average stereo reception within a 6 kHz tone frequency band would this is reduced to 2 kHz. With regard to monophonic communication facilities, the band would be reduced from, for example, 3 kHz to 1 kHz.

The sideband channel, in which less interference occurs, would reduce race to a lesser extent and in some cases there would be no change of the frequency band take place.

The invention is described in more detail below in exemplary form with guidance of the accompanying drawing, in which Fig. 1 shows a block diagram of a typical one receiver plant according to the invention, Fig. 2 is a block diagram of a switching device for switching low-pass filters to upper and lower sideband channels for improved performance, and Fig. 3 is a diagram for illustrating troublesome interference which may observed using a spectrum reproducing apparatus.

Fig. 1 shows the block diagram of the receiver according to the invention.

This type of receiver can be used to receive certain forms of amplitude modulated stereo signals, dwrs stereo signals with independent sideband, with the information in the left stereo channel mainly transmitted via one sideband and the information in the right stereo channel 7801100-4 Ken via the other sideband. The connection shown can also be used for receiving monophonic signals, in which case, in addition to improved selectivity also brings the advantage compared to reception of amplitude modulated monophonic signals that interference is separated in the room from the desired signal. The desired monophonic signal and several of the components of a stereo signal will appear to come from a point midway between the left and right speakers.

But interference in an adjacent channel above the desired channel will appear to come from a point to the left of the desired signal, while interference below the desired signal occurs appear to come from a point to the right of the desired signal len. As already pointed out, the listener is thus given the opportunity to distinguish the interference and favor the desired signal. In order to the way in which the device leads to improved selectivity, in Fig. 1 is studied.

An antenna 102 is connected to a superheterodyne coupling 104, working with high and medium frequency and whose intermediate frequency amplifier is applied to an amplifier 106. The output of amplifier 106 appearing on a line 107 is supplied with three separate steps, viz one step for the upper sideband, one step for the lower sideband and one step for carrier channel. The upper sideband step is insulated by a filter 108, which in turn feeds an amplifier 114, which then feeds a pro- product demodulator 118. The injection input of demodulator 118 is pre- connected to the carrier channel 110 via a line 111. The carrier channel is was reversed to select the carrier signal and provide a clean carrier. One suitable coupling for this purpose is described in U.S. Pat. scripture 3973203.

A variety of methods can be used for isolation and demodulation. ringing the information in the upper and lower sidebands of a signal with double sidebands by using phase shift couplings except for the coupling shown in Fig. 1. A method of receiving amplitude emulated stereo signals with independent sidebands are described in detail in U.S. Patent 4,018,994.

The lower sideband is selected by means of a filter 112, the output of which signal is applied to an amplifier 116, which in turn supplies a product demodulator 120. The demodulator 120 is also applied to the output signal from the carrier. the wave channel 110 via a line 111. In a variant of the product demodulators 118 and 120 may be replaced by flea demodulators. Through this exchange it would also be possible to exclude the carrier channel 110, but with respect to minimal tube distortion 7801100-4 and best signal-to-noise operation in outer areas is that shown in Fig. 1 the coupling with product demodulators is superior. If the envelope module used without the carrier channel stage, the upper and lower side the belt filters are still required for transmission of the carrier component, which complicates their data.

The output of the demodulator 118 is applied to an amplifier 122 and the output of the demodulator 120 an amplifier_124. The output signal from the amplifier 122 a high pass filter 138 is applied, which in turn supplies a detector 140. In the same way, the output signal from the the amplifier 124 a high-pass filter 142, which in turn supplies a detector 144. The filters 138 and 142 and the detectors 140 and 144 were used to measure the level of interference next to the desired sidebands. At too close current radio transmission, the carrier frequencies are on the conventional broadcast band for amplitude modulation, for example in the USA 10 kHz apart. The task of filters 138 and 142 is to insulate the interference signals in adjacent channels and must therefore transmit signals with the frequency 10 kHz with comparatively small attenuation. IN for the purpose of conveniently sensing the level of the carrier 1 adjacent channels the filters in the high frequency and intermediate frequency stage 104 and the band filters 108 and 112 have such a large bandwidth that signals are transmitted which are offset from the center or desired carrier frequency at least i 10 ikHz. _ The outputs of the detectors 140 and 144 are via lines 141 and 145 connected to a comparator 146, which determines which of the detectors torors emitting a higher level signal. If the detector 140 emits one larger output signal than the detector 144 can therefore be assumed that the cleaning to the upper sideband is greater than interference to the lower the sideband. The comparator 146 would then, for example, set the switching only the low pass filter 126 to lower cutoff frequency. If the output signal from the detector 144, which appears on the line 145, has a higher value than voltage on line 141, would conversely assume that interference to the lower sideband channel is larger and it would switch The low-pass filter 128 is switched to a lower cut-off frequency than filter 126.

The cut-off frequencies for filters 126 and 128 could be made depending on the level of interference or could jump in discrete steps.

Thus, for example, the channel in which the greater level of interference would be occurs is set to a cutoff frequency that is one - third of its normal total bandpass, which would be used when the channel receives a signal that is comparatively free from interference. For communication 7801100-4 7 _ __ _ i For this purpose, the cut-off frequency may be 1 kHz. The broadband filter, which measures smaller amounts of interference, in an embodiment of the invention maintained at its full broadband characteristics, or may be reduced race to bandwidth but to a lesser extent than the sideband in which it stronger interference occurs. The reason why it would be advantageous to in some situations reduce the frequency band in both the sidebands are that, if interference occurs in either sideband, this generally indicates that the desired signal is weak. By reducing its bandwidth, it therefore becomes possible to combat poor noise conditions countries.

The output signals from the switchable or controllable low-pass filters 126 and 128 are each supplied with amplifiers 130 and 132, as in in turn feeds, for example, the left speaker, which is supplied to the upper the band, and the right speaker, which is fed to the lower sideband.

While according to Fig. 1 filters are used for insulation of sidebands the invention can also be applied to phase shift for selection of sidebands.

Phase shift type receivers are well known, and for example in the above U.S. Patent 4,018,994 proposes a technique which is based on reception of sidebands with phase shift. In this patent specification shows a coupling which is particularly suitable for compatible amplitude modes. duplicated stereo reception, whereby this coupling can be modified with taking into account the advantages of the present invention by taking the outputs of Fig. 1 of the patent specification before the stereo signals speakers 68 and 70 are applied, and feed them to the one shown in Fig. 1 horizontal case showed the connection at the outputs of the amplifiers 122 and 124. The 1 Fig. 1 in the present case showed the part of the coupling before this point is of course no longer required, ie the whole coupling is included. the amplifiers 122, 124 and the blocks for feeding these amplifiers. kare would be excluded, as shown in Fig. 1 of the patent specification the stereo separation coupling performs all required signal processing, carried out by the excluded blocks. It can be emphasized that the displacement nets 68 and 60 in Fig. 1 of the patent specification must be changed with account of its structure, so that at least a small degree of band suppression is achieved at 10 kHz. While separation at this high re frequency is generally unnecessary with respect to stereo reception, is necessary to detect interference in adjacent channels in the present case. Separation of higher frequencies is also required the ability to select shall be fully exercised.

If the sideband is isolated by the filter 108 and demodulated by block 118 represents the upper sideband and the interference a 7801100-4- above the desired channel is greater than the interference below, more filter 126 to be switched to lower cutoff frequency than filter 128 and the interference will be attenuated. It is also possible to significantly reduce the high cut-off frequency of the low-pass filter in depending on the interference in the rack to use a switchable filter according to Fig. 1.

In a further embodiment of the invention, both are controlled filters 126 and 128 by reducing their cutoff frequencies, but the channel that is exposed to the larger interference is coordinated with the lowest cut-off frequency.

Instead of using high-pass filters that are connected to the output of amplifiers 122 and 124, bandpass filters can be used, such as are connected to the output of amplifier 106, dwrs connected in conduction 107. But whether such filters should have the task of producing reasonable selectivity, they would be slightly more expensive than those in block form in Fig. 1 shows the filters, dwrs the high-pass filters 138 and 142.

The output signals from filters 126 and 128 are applied to the amplifiers 130 and 132, which feed converters in the form of speakers or stereo headphones. When properly placed speakers at a space e.g. in home installations of approx. 1.2_til1 1.8 m and in motor vehicles or other confined spaces at smaller intervals or when using headphones of stereotype was used in receiving monophonic signals with dual sidebands with identical information in the two sidebands, the selector's ability is used to distinguish interference in neighboring true channels. If, for example, interference in an adjacent channel below the desired channel, i.e. the channel next to the lower sideband in it desired signal, appears to the left of the listener, appears in- the reference in the adjacent channel above the desired channel, i.e. the channel next to the upper sideband of the desired signal, to the right about the listener. The desired upper and lower sideband information is entered in phase to the speakers, so that the listener gets the impression that it wanted the signal comes from the center, dwrs halfway between the speakers. To As a result, the listener has the opportunity to use his or her choice and distinguish the interfering signals, which will occur at side of the listener. The same effect exists to some extent in question about the above-described amplitude modulated stereo embodiment according to the invention except that the lower sideband interference would perform to the right of the listener and the upper left. But after- as the desired signal components do not all appear in the middle, but can appear in places closer to the speakers, the listener gets less selectivity. 7801100-4 9 _H _.... .i. ii, W, .i ii _ Fig. 3 illustrates a typical spectrum situation for a conventional amplitude modulated broadcast system, where the desired carrier the frequency is denoted by Fc. The adjacent channel 10 kHz above the desired carrier is denoted by Fc + 1. The carrier in the adjacent channel 20 kHz above occurs at Fc + 2. In the same way, they have The lower frequency Ierating signals in adjacent channels carry wave frequencies FC-1 and Fc-2. It can be emphasized here that considerable band overlap exists, as most broadcast stations for high quality amplitude modulation works with sideband components which is significantly higher than 5 kHz. The sideband components from adjacent channel stations can therefore be within the passband of the desired signal len. When this is the case, they give rise to an unusual type of interference which is sometimes called monkey nights and is incomprehensible and very unpleasant to intercept.

Even if a receiver completely eliminates carrier the component of the interference in the adjacent channel it thus comes to be subject to interference from the sidebands of the signals in the adjacent true channel. By considerable attenuation of signals closer than 10 kHz from the desired carrier, the invention not only causes the hovering with the frequency 10 kHz is removed, but also that the sideband interference or the monkey night is considerably dampened. In the example shown in Fig. 3 is the interference from the interfering signal in the adjacent channel above the carrier frequency considerably stronger than the interference from it interfering signal in the lower sideband. It is therefore essential that the frequency band of the receiver is significantly reduced with respect to its upper sideband components. If the receiver were placed on one place where its lower sideband would be exposed to the higher level of purity, it would be necessary to introduce additional white for the lower sideband. In general, frequency allocation takes place in such a way that very insignificant interference within a certain range from adjacent channel signals, which are down at a distance of 10 or 20 kHz from a particular assigned station. However, if a listener tunes to a remote station, there is a good chance that it will be exposed to ference 1 adjacent channels.

As already pointed out, according to the invention, listening selectivity of the recipient to improve the recipient's ability to eliminate interference from the adjacent channel. For the realization of the selectivity requires the apparent location of the desired sound. the source in the room is different from the apparent source of the interfering 7au11oo-4g 10 - Pray or disturb the signals. It is therefore essential that the the separation both with respect to the stereo embodiment according to the invention one and the monophonic embodiment is effective for all components that occur within the effective high-frequency limit for the frequency pass band. However, it is not as important that is large with respect to the low frequency portion of the audible pass. band, since interference components in adjacent channels in the will not appear close to the carrier of the desired signal. wave. In the monophonic version, therefore, they need circuits that separation of the sidebands does not make them particularly effective consideration for frequencies eg below 1 or 2 kHz. If the phase shift the principle was used for the separation of the upper and lower sidebands therefore, these circuits do not accurately accomplish phase correction at the low frequency range, so that fewer components are consequently required. In the case of amplitude modulated stereo reception, se- pairing for both stereo performance and interference reduction.

Should the circuits used for amplitude modulated stereo reception be reasonable separation is therefore required, eg down to at least 300 Hz.

In the development of it in U.S. patents 3218393, 3908090, 3947749 and 4018994 described stereo system for amplitude modulation further provides those included in the receiver phase shift networks reasonable separation, d'vs 20 dB or more from 200 Hz to 5000Hz. But the receiver's total monophonic frequency band is slightly larger, d'vs up to 10 kHz. The reason for not using circuits for separation at the higher frequencies is that the high frequency the sounds only give rise to insignificant stereo information, if sufficient information is available in the low range and mid range for to enable someone to identify the place. As a result of eco- economic and other reasons, the separation has therefore been limited to approx 200 to 5,000Hz as above, which is mainly suitable for stereo transmitter separation properties.

In the present case, it is desirable to use comparatively good separation for the entire high-frequency band of the plant, so that the conference can be isolated and the listener's selectivity can be fully utilized.

But the separation does not have to be very large to achieve that the listener can distinguish the interference and is generally a ring of 10 dB sufficient. If the embodiment of the invention is used in which further filtration of the interference occurs, furthermore, the separation only needs to be so large that the plant can measure the level of the interfering signal. When the equipment was used 7801100-4 11 E facilities where the carrier frequency of the interference is known, such as is the case with conventional amplitude modulated rotating, ie 10 kHz from the desired carrier, eg the separation only needs be reasonable at 10 kHz. It is therefore not necessary to make use of the full selection capacity of the trader, taking into account the frequency components if they are strong enough to be disturbing, eli- minimized or at least significantly attenuated due to low-pass filtering. ring at the coupling shown in Fig. 1. In fact, the net can designed in such a way that the separation is poor, eg above some kilohertz, as long as it is maintained at 10 kHz. As a result of compos- simpler data, costs and complexity can be reduced. considerably with regard to the means for effecting separation of the upper and lower sideband components.

Taking into account information on the construction of phase shift reference is made to the article Normalized Design of 900 Phase-Differential ence Networks by S.D.Bedrosian in IRE Transactions of the Professional Group on Circuit Theory, Volume CP-7, No. 2, pp 128-136 (June 1960) and the literature references cited here.

Fig. 2 shows a switching device which can be used for achieving the desired improved selectivity. An electronic current switch 200, which is composed of sections 202, 206, 208 and 212, was used to change the frequency band of the system from the maximum frequency frequency band (position 2) for reducing the upper sideband width to 2kHz (mode 1) and reduction from the maximum bandwidth (mode 2) of it lower sideband to 2kHz (mode 3). If the switching device is inserted In rig 1, it would be controlled by the comparator 146 and would be used 1 instead of filters 126 and 128. Switch section 208 and sec ~ 212 was used to change the frequency band of the plant to it lower sideband information. All switch sections are mechanical interconnected, so that they change positions in synchronism. In that in Fig. 2 shown setting mode, the upper sideband is limited with regard to to the limit range to 2 kHz by means of the low-pass filter 204 and the lower one the sideband to 3 kHz by means of the low-pass filter 210. If the contacts are controlled to position 3, as would be the case in case of troublesome interference with the lower sideband, the lower sideband is limited to an area of 2 kHz and the upper sideband to 3 kHz. When interference is missing or has a low level, the contacts would be set to position 2, so that the clean is disconnected and maximum frequency width is obtained. In some cases, it may be desirable to connect only one filter and allow the other sldband work with maximum bandwidth. Such a switch can be easy Q 7801100-4 is achieved by changing the coupling shown in Fig. 2 by remove the filter 210 and connect the lead, which previously leads to the input of the filter 210, to the line which previously leads to the time on filter 210.

The tone frequency filters 204 and 210 can of course be placed on one number of other places or of course a combination of filters can be used to achieve the desired selectivity. Filter characteristics can be changed in discrete steps or can be continuous. Furthermore, can the filters be of the passive type, as described in, among other things, the publication Filter Design Data for Communication Engineers by J.H.Mole, John Wiley & Sons, Inc., New York, 1952. Active tone frequency filters can also be used. das, and such filters are described, inter alia, in the publication Raoid Practical Designs of Active Filters by D.E.Johnson and J.L.Hilburn, published by John Wiley & Sons, Inc., New York, 1975.

Claims (14)

7801100-4 F Claim 7, _ du A method of reducing interference between adjacent channels when receiving an amplitude modulated signal, which is reproduced in the form of a binaural two-channel signal, characterized in that the upper and lower sidebands of the amplitude modulated signal are demodulated and the demodulated slides are supplied to each binaural channel, that the level of the received interference with the adjacent channel in the demodulated upper and the demodulated lower sideband is measured and that the tone frequency band is reduced in the channel of the binaural channels which has the larger level of interference, when this level exceeds a predetermined value. A method according to claim 1 to reduce interference between adjacent channels in an amplitude modulated stereo signal with independent sidebands, characterized in that during the measurement the received interference in the demodulated upper and the demodulated lower sideband in the stereo signal is measured and that the reduction of the tone frequency band is applied to the channel of the stereo channels that has the greater level of interference. 3. A method according to claim 1 or 2, characterized in that the tone frequency band is further reduced in the binaural channel or stereo channel with the lower interference level but by an amount less than the reduction to which the other channel is exposed. 4. A method according to claim 1, 2 or 3, characterized in that the predetermined level value is selected equal to about 0.1% of the energy level of the amplitude modulated signal sideband. 5. A method according to any one of claims 1-4, characterized in that the tone frequency band in the binaural channel or stereo channel, in which the higher interference level occurs, is reduced to about one third of the entire bandwidth of the channel. 7 6. A method according to any one of claims 1-5, characterized in that the tone frequency band in the binaural channel or stereo channel, in which the higher interference level occurs, is reduced to about 2 kHz. 7. A method according to any one of claims 1-6, characterized in that the tone frequency band in the binaural channel or stereo channel, in which the higher interference level occurs, is reduced to about 2 kHz and in the other channel to about 3 kHz. Receivers for performing the method according to one or more of claims 1-7 and reproducing an amplitude modulated signal in two uv 7801100-4 14 see f »- 2 .... ha binaural channels, wherein the received signal is converted into a flour lane frequency signal which is then demodulated, characterized by a device for modifying the bandwidth of one channel relative to the other and achieving better suppression of interference with adjacent channels, comprising on the one hand a demodulator (108, 114, 118 and 112, 116, 120) for each of the upper and lower sidebands of the amplitude modulated signal, which demodulators emit demodulated sideband signals, and a pair of binaural output channels (L, 130, 134 and R, 132, 136) for reproducing each demodulated sideband signal. an interference level detector (138, 140 and 142, 144) for reacting for each of the demodulated sideband signals and detecting the level of interference with the adjacent channel in the respective demodulators. ad signal and a signal modification step (126, 128) in each binaural channel, which are connected to and controlled by their respective detectors (138, 140 and 142, 144) and modify the tone frequency band in the channel of the binaural channels with the larger interference level by reducing the bandwidth of the channel, when the interference level exceeds a predetermined value. 1 Receiver according to claim 8, further characterized by a comparator (146), which is connected to and controlled by the level detectors (138, 140 and 142, 144) in both channels and compares the interference level in these channels, wherein the comparator is connected to and controls the two modification steps (126, 128) by reducing the tone frequency band in the channel with the larger interference level. Receiver according to claim 8 or 9, characterized in that the modification steps are controlled low-pass filters (126, 128). A receiver according to claim 8, 9 or 10, wherein the receiver is a stereo receiver operating with amplitude modulated signals and the binaural channels are stereo channels, characterized in that the demodulators (108, 114, 118 and 112, 116, 120) demodulate between the frequency signal and generates a pair of stereo outputs, which are substantially separated from interference signal components over 5 kHz, and that the modification steps (126, 128) reduce to about 2 kHz the tone frequency band of the stereo channel in which the higher interference level occurs. 12. A receiver according to claim 11, characterized in that the stereo output signals from the demodulators are substantially separated from the interference signal components having a frequency up to at least 10 kHz and that the modifying steps reduce the tone frequency band in the stereo channel by about one third of the total bandwidth of this channel. 7801100-4 Receiver according to one of Claims 8 to 12, characterized in that the detectors (138, 140 and 142, 144) react for an interference level of sideband energy, when a predetermined value of approx. 0.1% of this energy level is sensed. A receiver according to any one of claims 8-13, wherein the receiver is a stereo receiver and the binaural channels are stereo channels, characterized in that the detectors (138, 140 and 142, 144) respond to an interference level of sideband energy, when a predetermined value of about 0.1% of the sideband energy level is sensed. PROMISED PUBLICATIONS: