JPS6121636A - Receiver reduced in interference of adjacent channel - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Although the present invention has a wide range of applications, it is particularly suited for use in reducing adjacent channel interference effects from AM monophonic systems to AM stereo systems, and is particularly described. do.

Conventionally, there are many methods for reducing the interference effects of adjacent channels, including manually or automatically operated variable selectivity filters and manually adjusted audio or IF notch filters to provide sharp discrimination against interference. means are used. For example, John Willey, New York City,
And, Sons, Inc. (John W.
Radio, Receivers, by R. Sturley, published by iley & 5ons Inc.
Please refer to pages 517, 518 and 543 of Design J'517.

Also, a number of systems have been developed that automatically change receiver selectivity as a function of interference. Selectivity may vary symmetrically or asymmetrically.

A description of such a system can be found in Starley's article 5 above.
Found on page 43.544. Changes in selectivity are provided at intermediate frequencies as well as in the sensing system.

It is an object of the present invention to provide an inexpensive automatic device for reducing interference while maintaining relatively good frequency response.

The present invention utilizes the so-called "cocktail party effect" to further discriminate against interference. The "cocktail party effect" is an effect that allows binaural listeners to separate speech arriving from two different speakers, allowing them to pay greater attention to the other speaker. It is.

This refers to the ability of humans, who have both ears, to be able to hear only one story while distinguishing it from the other, even when many people are speaking different stories at the same time in one room. This is because the different stories in the room originate from different points and therefore reach the listener from different directions.

In AM stereo receivers of the type designed to receive independent sidewave stereo signals, if the stereo decoder circuit is designed to have excellent stereo separation of approximately 5 KHz or better, listen now. +10 from the broadcast station
Adjacent station interference caused by a broadcast station 10 KHz away will be heard primarily only on the right channel, and adjacent station interference caused by a broadcast station 10 KHz away will be heard mainly only on the left channel. So, if you try to listen to the station you want now, the broadcast from this station will mainly sound like a recording of the sound coming from the center of a stereo sound system.1. Adjacent channel interference can be heard as if the sound is coming from either the far left or the far right, so if we take advantage of the cocktail party effect that humans have, we can create a receiver that can discriminate against adjacent channel interference. is obtained.

The primary objective of the present invention is to enable listeners of AM monophonic and stereo signals to take advantage of the "cocktail party effect".

The invention can be used for the reception of amplitude modulated waves, and is particularly suitable for the reception of AM stereo waves of the type consisting of: The invention may, for example, measure the level of received interference in the upper sideband stereo channel caused by the jamming channel adjacent to the upper sideband of the desired signal, Measure the level of received interference in the lower sideband stereo channel caused by the channel, and (C) measure whether (a) is greater when the stronger interference level exceeds a predetermined level. automatically reducing the audio frequency response of the stereo channel experiencing the greater interference level according to the magnitude of the interference of adjacent channels in the reception of AM stereo modulated waves of the ζ Two Independent Sideband (ISB) type; can be used to reduce

In many applications of the invention, it is desirable to attenuate both channels above and below a desired channel by a greater factor than when the system is operating substantially without interference. However, it is desirable to provide greater attenuation to adjacent channels that experience greater interference levels.

The invention can also be used to improve the performance of monophonic reception systems by allowing listeners to take advantage of the "cocktail party effect". One way to improve adjacent channel interference in a monophonic double sideband signal receiver is to separate and demodulate both the upper and lower sidebands of the desired signal and send the resulting audio waves to separate transducers. It includes each step of sending it to the appropriate circuit to drive it.

The transducer may be a stereo speaker, ie, a speaker mounted as a speaker spaced approximately 120 cm to 180 cm apart. The invention can also be implemented by using a stereophonon as a transducer.

There are many ways to separate and demodulate upper and lower sideband channels, including phase-shifting and filter-based systems. Such techniques are well known to those skilled in the art. Systems with full carriers or double sideband low band carriers or suppressed carriers can be used, ie systems with carrier levels lower than the peak coupling amplitude of the sidebands or full carriers are used.

A monophonic application of the present invention also provides an apparatus for measuring the interference level of channels adjacent to the "double sideband components" of a desired signal and reducing the audio frequency response of channels experiencing higher interference levels. can be used. Thus, the listener not only has an improved interference reduction effect based on the cocktail party effect, but also a sound system with improved selectivity.

The present invention is particularly useful in dual independent sideband (ISB) type stereo reception, Cock signal receivers, where stereo-related information appears in sideband modulation above and below the carrier wave.

In one such type of signal, the carrier wave is amplitude modulated with a stereo total (L-1-R) intelligibility and simultaneously phase modulated with a stereo difference' (L-R) intelligibility.

Such stereo waves are described, for example, in U.S. Patent No. 3.218,3.
No. 93 and No. 3,908,090. Such stereo wave receivers typically operate at intermediate frequencies and are designed to accentuate the cocktail party effect by providing special characteristics of phase-shifting sideband separators, such as those provided by superheterodyne type circuits. Can be configured. Phase-shifting separation devices, unlike conventional stereo receivers, will provide substantial separation of interfering signal components of adjacent channels, such that the frequency range is typically 5 KHz or higher, which is an acceptable high frequency range for stereo separation components. . By connecting the output of the phase-shifting sideband separator to a device that separately amplifies the audio output of the sideband separator, the interference component for one sideband can be reduced by one stereo speaker. The interference components of adjacent channels in other sidebands will be reduced by the other stereo loudspeaker.

The desired stereo component will fall approximately within the range between the two speakers, as is usual for stereo illusions.

In both stereophonic and monophonic reception, audio frequency response reduction should only be applied when the worst sideband channel interference is of sufficient amplitude to cause audibility problems. Typically,
If the power level of the interference is less than one-tenth of one percent of the desired sideband power level, there is no need to reduce the audio frequency response. Typically, the response of a channel experiencing stronger interference levels is reduced by a factor of 1/3 of the channel's total response. For example, a stereo reception of 6 K11z audio response with medium sound quality would be reduced to 2 KHz. In the case of monophonic, the response is, for example, 3KIlz
to I KHz. The side that experiences less interference will be reduced to a lesser extent, and in some applications of the invention, the side that experiences weaker interference will have no change in frequency response.

In order to better understand the invention and to appreciate other objects of the invention, reference will now be made to the drawings.

FIG. 1 is a block diagram of a receiver implementing the invention. This type of receiver is used to receive AM stereo signals of the type consisting of two independent sidebands (ISB) stereo signals, in which essentially the left stereo channel information is contained in one sideband. is transmitted via
The right stereo channel information is transmitted via the other sideband. The illustrated circuit can also be used to receive monophonic signals. When used to receive monophonic signals,
In addition to providing improved selectivity, this provides the additional advantage over conventional AM monophonic reception of spatially separating interference from the desired signal.

Many of the desired monophonic and stereo signals are
It sounds like it's coming from a point halfway between the left and right speakers. However, interference between adjacent channels above the desired channel will sound like it is coming from a point to the left of the desired signal, and interference below the desired signal will sound like coming from a point to the right of the desired signal. As mentioned above, this allows the listener to discriminate the interference and specifically select the desired signal. It is necessary to examine Figure 1 to understand how this system provides improved selectivity.

An antenna 102 is connected to an RF-TF superheterodyne circuit 104. The IF output of 104 is the amplifier 10
Sent to 6. The output of 106 is applied to line 107, which is connected to three separate circuits: upper sideband, lower sideband,
sent to the carrier channel circuit. The upper circuit is divided by a filter 108 which is connected to an amplifier 114 which in turn is connected to a product demodulator 118. The inlet of the product demodulator 118 (
The carrier channel 110 is connected to the carrier channel 110 by line 111. The carrier channel is used to select the carrier signal and provide a clean carrier wave. One circuit adapted for such an operation is described in U.S. Pat. No. 3,973,203.

There are many methods for improving intelligibility and demodulation in the upper and lower sidebands of both sidebands, including phase-shifting systems in addition to the system shown in FIG.

The lower sideband is selected by filter 112 which is connected to amplifier 116 which in turn is connected to product demodulator 120 . Product demodulator 120 is further connected to carrier channel 110 through line 111. In one form of this system, envelope demodulators may be used in place of product demodulators 118,120. Such a configuration would also allow carrier channel 110 to be eliminated. However, in order to minimize distortion and obtain the best signal-to-noise ratio at the fringe area locations, a circuit utilizing a product demodulator as shown in FIG. 1 is superior. Also, if an envelope demodulator is used without a carrier channel circuit, the upper and lower sideband filters would be required to pass the carrier component, which would complicate their specifications.

The output of the product demodulator 118 is supplied to an amplifier 122 and the output of the product demodulator 120 is supplied to an amplifier 124. Amplifier 12
The output of 2 is supplied to a bypass filter 138 and then to a detector 140. Similarly, the output of intensifier ij 124 is fed to bypass filter 142 and then to detector 14.
4. Filter 138, 142 and detector 1
40.144 is used to measure the level of interference adjacent to the desired sideband.

In current broadcasting services, the standard AM broadcast band in the United States is 1.
Separated by 0KIIz. Filter 138.142
is used to separate common channel interfering signals.

Therefore, filters 138, 142 pass 10 KHz waves with relatively little attenuation.

To conveniently sense the level of adjacent channel carriers, the filters of RF and IF circuit 104 and sideband filters 108 and 112 are wide enough to pass signals that are at least ±1QKIIz off center or desired carrier frequency. It is necessary.

The outputs of detectors 140 and 144 are connected to lines 141 and 145.
is connected to the comparison circuit 146 through.

Comparison circuit 146 evaluates which detector produces a large level wave. However, if the detector 140 is 144
If a larger power is generated, it can be assumed that the interference in the upper sideband is greater than the interference in the lower sideband. The comparison circuit 14'6 includes, for example, a switchable low-pass filter 126.
Toggles the downward cant-off frequency adjustment. On the contrary, detector 1
44 appears on line 145 and line 141
, the interference towards the lower sideband channel is greater and the switchable low-pass filter 128 will switch to a lower cutoff frequency than the filter 126.

The cutoff frequencies of filters 126 and 128 can be a function of the interference level and can be jumped in steps. For example, a channel experiencing significant levels of interference may be set to a cutoff frequency that is one third of the normal total bandpass used when this channel is receiving signals relatively free of interference. For communications services, this cutoff frequency is 11Hz. In the first embodiment of the present invention, the wideband filter for measuring the amount of lower interference is either left with the full wideband characteristic or reduced in band 11 by an amount slightly less than the sidebands that suffer from stronger interference. I'll keep it.

The reason it is advantageous to reduce the frequency response of both sidebands is that if either sideband is experiencing interference, the desired signal will generally be weakly indicated. This mid-band reduction therefore helps overcome bad noise conditions.

Switchable or controllable low-pass filter 126.12
The outputs of 8 are supplied to intensifiers 1301 and 132, respectively.
Then, for example, a left transducer is fed with the upper sideband and a right transducer is fed with the lower sideband.

In typical applications of such devices, the transducer is generally a loudspeaker, although a stereophone is often used.

FIG. 3 shows a typical spectral situation for a standard AM broadcast system, where the desired carrier frequency is designated Fr. The adjacent channel 10KH2 above the desired carrier frequency is designated FC+1. Further, the adjacent channel of 20Kllz I- is indicated by FC+2. Similarly, the lower ones are indicated by FC-1 and FC-2.

The aim of the invention is to improve the reception performance in this type of interference.

Since even the best AM broadcasting station has sideband components of 5 KHz or more, it should be considered that there is considerable sideband overlap. This sideband component from the common channel can therefore be included in the passband of the desired signal. In this case, a rare type of interference called "monkey chatter" occurs, which can be extremely audible and impair intelligibility.

Therefore, even if the receiver completely eliminates the carrier component of adjacent channel interference, it still suffers from interference from the sidebands of adjacent channel signals. The present invention significantly attenuates nearby signals within 10 KHz of the desired carrier, thereby reducing the frequency of 10 MHz.
Not only does it help eliminate heterodyne whistling, it also greatly attenuates sideband interference or monkey chatter. Third
In the illustrated example, the interference from adjacent channel interfering signals above the carrier frequency is considerably stronger than the interference from lower sideband interfering waves. Therefore, it is important that the sensitivity of the receiver is substantially reduced for upper sideband components.

If the receiver is located at a point where the lower sideband experiences a large amount of interference, an additional selection state for the lower sideband must be switched.

It is true that frequency assignments are such that in a given area there is little interference from adjacent channel signals 10 or 20 KHz away from the assigned station. However, if a listener tunes in to a distant station, the likelihood of experiencing adjacent channel interference is high.

As mentioned above, the present invention utilizes the so-called cocktail party effect to enhance the adjacent channel interference rejection characteristics of the receiver.

The realization of the cocktail party effect requires that the apparent location of the desired sound source be spatially separated from the apparent source of the interfering waves. Therefore, in both the AM stereo embodiment of the C1 invention and the monophonic example, it is important that the sideband separation be effective for all components within the 11 effective frequency limit of the audio bass hunt. However, for the low frequency part of the audio path hand, this separation is thick (Jl-, which is not important).

This is because the interfering components of adjacent channels are generally not close to the carrier of the desired signal. Thus, in the monophonic example, the circuitry providing sideband separation need not be particularly effective for frequencies below, for example, 1 or 2 KHz. Therefore, if a phase-shifted system is used for upper and lower sideband separation, the network need not provide precise phase correction in the lower frequency range and may have fewer components.

In the case of AM stereo, separation is required for both the stereo effect and the interference reduction effect. Therefore, frequencies fl used in AM stereo require adequate separation, eg, at least 300 KHz or less.

Further, in this example, it is desirable to provide relatively good isolation for all high frequency responses of the system so that interference is isolated and the cocktail party effect is fully exploited. However, this separation need not be so great that a listener can discern the interference. Generally, 10 db of separation is adequate.

Furthermore, if additional filtering of adjacent channel interference is applied in the implementation of the present invention, then measuring the level of the interfering waves alone is sufficient for isolation. For example, if the carrier frequency of adjacent channel interference is known, it is possible to immediately
If KHz is known, only separation that is adequate at 10X) is required. Therefore, if these frequency components are strong enough to cause disturbances, it is unnecessary to give them a full cocktail party effect using IL, and they can be removed by a low-pass filter as shown in Figures 1 or 3. It can be greatly attenuated to a lesser extent. In practice, as long as the network is restored to 10 Kllz, the separation can be roughly constructed, for example over several tens of KHz. The simplicity of this specification allows for substantial cost and multi-Gft savings for means of providing separation of upper and lower sideband components.

FIG. 2 shows the switch arrangement used to provide the desired improved selection effect. The electronic switch 200 consists of parts 202, 206, 208, and 212, and the upper sideband response is 2Kll from the total response (position 2).
It is used to change the frequency response of the system to reduce the lower sideband from the total response (position 2) to 2KII2 (position 3). This switching circuit, when applied to FIG. 1, is controlled by comparator circuit 146 and is used in place of filters 126 and 128. Switches 208 and 212 are used to change the frequency response of the system to lower sideband intelligibility. All switches are interlocked and change position together. In the position shown in FIG. 2, the upper sideband has a frequency response of 2KII by the low-pass filter 204.
z, and the lower sideband is limited to 3Kllz by the low pass filter 210. If severe interference is in the lower sideband, and the switch is in the third position, the lower sideband is limited to a 2 KHz response and the upper sideband is limited to a 3 KHz response.

When there is no interference or its level is low, the switch is operated to the second position, disabling the filter and providing maximum frequency response.

In some systems, it is desirable to include only one filter varnish and control the other sidebands to work over the entire response. Such a switch configuration is obtained by removing the 'ζ filter 210 and replacing this filter 21 with the circuit shown in FIG.
This can be easily obtained by modifying FIG. 2 by connecting the lead that is in the input of 0 and the lead that comes out from the output.

Audio filter 204 for the field of the path of jυ1
and 210 can be placed at many other points,
Combinations of these filters can also be used to achieve desired selectivity improvements. The characteristics of the filter may be discontinuously stepped or continuous. The filter may also be passive, using designs such as those found in many publications. You can also use active audio filters.

In all embodiments, the configurations described above are merely illustrative of possible specific embodiments. Of course, many variations can be made without departing from the spirit of the invention.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a typical receiving system constructed in accordance with the present invention; FIG. 2 is a schematic block diagram showing a switching arrangement for switching the low-pass filter to upper and lower sideband channels to improve coherence; l1, Figure 3 is a sketch showing the severe interference that may appear on a spectral display. 102... Antenna 104... RF-IF superhetero gain circuit 106... Multiplier 11 107...
Line 108...Filter

Claims (1)

[Claims] I A receiver for receiving dual independent sideband RF/AM stereo signals with stereo-related intelligibility manifested as upper and lower sideband modulation of a carrier, emphasizing the "cocktail party effect" A receiver configured to: (a) receive an RF/AM stereo signal of the above type and convert the received RF signal into an intermediate frequency (IF) signal; In response, this signal is demodulated and 5
(c) a device for producing a pair of stereo output signals with substantial isolation relative to interfering signal components of adjacent channels, such as those of KHz or higher; and (c) providing the stereo output signals of the sideband separation device to separate stereo audio output channels. equipment, and a receiver including. II. A receiver as claimed in claim I, wherein said demodulator provides substantial isolation for signal components with frequencies up to at least 10 KHz.