JPS6341254B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Although the invention has a wide range of applications, it is particularly suited for use in reducing the interference effects of adjacent channels from AM monophonic systems to AM stereo systems. I will explain about it.

Conventionally, there are many means to reduce 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. is used. for example,
John Wiley & Sons, Inc., New York City
See "Radio, Receivers, Design" by K. R. Sturley, published by Sons Inc., pp. 517, 518, 543.

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 on pages 543 and 544 of the Starley article cited above. Changes in selectivity are provided at intermediate frequencies as well as in the sensing system.

It is an object of the invention to provide an inexpensive and automatic device for reducing the interference effects of adjacent channels.

The present invention utilizes the so-called "cocktail party effect" to discriminate against the interference effects of adjacent channels. 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 one speaker. It is.

This refers to the ability of humans, who have both ears, to be able to hear 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 speeches within a room all originate from different points and therefore reach the listener from different directions.

In a type of AM stereo receiver designed to receive independent sidewave stereo signals, if the stereo decoder circuit is designed to have excellent stereo separation of approximately 5KHz or higher, Adjacent station interference caused by a broadcasting station that is +9KHz away from the broadcasting station will be heard mainly only on the right channel, and adjacent station interference caused by a broadcasting station that is -9KHz away will be heard mainly only on the left channel. So, if you try to listen to the desired station, you will hear that the broadcast from this station is mainly coming from the center of a stereo sound system, but adjacent channel interference causes the sound to come from either left or right. If we utilize this human characteristic called the cocktail party effect, we can obtain a receiver that can discriminate against adjacent channel interference.

The primary purpose of the present invention is to make the "cocktail party effect" available to listeners of AM monophonic and stereo signals.

The present invention can be used to receive amplitude modulated waves, and in particular,
Suitable for receiving certain types of AM stereo waves. The invention includes, for example: (a) means for receiving an RF/AM stereo signal of the type described above and converting the received RF/AM stereo signal into an intermediate frequency signal (IF); (b) means responsive to said intermediate frequency signal; means for demodulating the lever signal to produce a pair of stereo output signals in which adjacent channel interference components falling at 5 KHz or above are substantially separated; and (c) providing said stereo output signals to separate stereo low frequency output channels. The method can be used to reduce the effects of adjacent channel interference in the reception of dual independent sideband (ISB) AM stereo modulated waves.

The present invention can be used to improve the performance of monophonic reception systems by allowing listeners to take advantage of the "cocktail party effect". One method 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 then 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, that is, a speaker installed as speakers spaced apart on the order of 120 cm to 180 cm. The invention can also be implemented by using a stereo headphone as a transducer.

There are many ways to separate and demodulate the 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.

The present invention particularly applies to dual independent sidebands (ISB) where stereo-related information appears in the upper and lower sideband modulations of a carrier wave.
This is useful for receivers of type stereophonic signals. In one such type of signal, the carrier is amplitude modulated with stereo total (L+R) intelligibility and simultaneously phase modulated with stereo difference (L-R) intelligibility. Such stereo waves are described in detail in, for example, US Pat. No. 3,218,393 and US Pat. No. 3,908,090. Such stereo wave receivers usually operate at an intermediate frequency and provide special characteristics of an ISB stereo signal demodulator or phase-shifting sideband separator, such as that provided by a superheterodyne type circuit. Therefore, it can be configured to emphasize the cocktail party effect. The ISB stereo signal demodulator according to the present invention, unlike conventional stereo receivers, provides substantial separation of adjacent channel interfering signal components above 5KHz, which is typically an acceptable high frequency range for stereo separation components. Will.
By connecting the output of the demodulator to a device that amplifies the audio output of the demodulator separately, the interference component for one sideband can be attenuated by one stereo speaker and the interference component for the other sideband can be attenuated. The interference components of adjacent channels of the band will be reduced by the other stereo loudspeaker. The desired stereo component is approximately 2, as is usual for stereo illusions.
It will fall within range between two speakers.

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 embodying the invention. This type of receiver is used to receive a type of AM stereo signal, namely a dual independent sideband (ISB) stereo signal, in which essentially the left stereo channel information is transferred to one sideband. The right stereo channel information is transmitted via the other sidebands. The illustrated circuit can also be used to receive monophonic signals. When used to receive monophonic signals, it provides the additional advantage over conventional AM monophonic reception of spatially separating adjacent channel interference from the desired signal.

Most of the desired monophonic and stereo signals will sound like they are coming from a point midway between the left and right speakers. However, interference between adjacent channels above the desired channel will, for example, 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 due to the cocktail party effect. To understand how this system has been improved, it is necessary to examine Figure 1.

An antenna 102 is connected to an RF-IF superheterodyne circuit 104. The IF output of 104 is sent to amplifier 106. The output of 106 appears on line 107, which is sent to three separate circuits: upper sideband, lower sideband, and carrier channel circuits. The upper sideband is selected by filter 108 which is connected to amplifier 114 which in turn is connected to product demodulator 118. The reference signal input to product demodulator 118 is connected to carrier channel 110 by line 111. The carrier channel is used to select the carrier signal and provide a clean carrier reference signal. One circuit adapted for such an operation is described in US 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 sideband filter system shown in FIG.

The lower sideband is selected by filter 112;
This filter 112 is connected to an amplifier 116, which in turn is connected to a product demodulator 120. Product demodulator 120 is further connected to carrier channel 110 through line 111. In one form of this system, product demodulators 118, 12
An envelope demodulator may be used instead of 0. 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. Furthermore, if an envelope demodulator is used without a carrier channel circuit, the upper and lower sideband filters will be required to pass the carrier component, which will 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.

In current broadcasting services, the US (Japan)
The AM standard broadcast band is separated by 10KHz (9KHz).

In typical applications of this system, the transducers provided by amplifiers 130, 132 are typically loudspeakers, although stereo headphones are also often used.

Figure 2 shows a typical spectrum condition of a standard AM broadcast system, where the desired carrier frequency is
Denoted by F _c . The adjacent channel 10 KHz above the desired carrier frequency is designated F _c +1. Also, the adjacent channel on 20KHz is indicated by F _c +2. Similarly, the lower one is F _c
-1 and F _c -2.

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

Even the best AM broadcasting stations have sideband components of 5KHz or higher, so 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.

It is true that frequency allocation is 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, there is a high possibility that the listener will experience adjacent channel interference.

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

In order to realize the cocktail party effect, the apparent location of the desired sound source must be spatially separated from the apparent source of the interference waves. Therefore, the present invention
In both the AM stereo embodiment and the monophonic example, it is important that the sideband separation be effective for all components at the high effective frequency limit of the audio passband. However, for the lower frequency portion of the audio passband it is not important that this separation be large. 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 accurate phase correction in the lower frequency range and may have fewer components.

In the case of AM stereo, separation is required for both stereo effects and interference reduction effects. Therefore, the circuitry used for AM stereo requires 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, 10db separation is appropriate.

If the carrier frequency of the adjacent channel interference is known, ie, 10 KHz (9 KHz) from the desired carrier, only separation that is adequate at 10 KHz (9 KHz) is required. Therefore, it is unnecessary to apply a full cocktail party effect to these frequency components if they are strong enough to cause disturbances, and they may be removed by a low-pass filter such as that shown in Figure 1, or at least significantly reduced. It will be attenuated. Actually the circuit network is 10KHz (9KHz)
As long as it is appropriate, that is, 10 dB, it can be roughly configured to be several KHz or more. The simplicity of this specification allows for a substantial reduction in cost and complexity of the means for providing separation of upper and lower sideband components.

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, and FIG. 2 is a sketch illustrating severe interference that may appear on a spectral display. 102... Antenna, 104... RF-IF superheterodyne circuit, 106... Amplifier, 10
7... Line, 108... Filter, 110...
Carrier channel, 111... line, 112...
...filter, 114, 116...amplifier, 11
8,120... Product demodulator.

Claims (1)

[Claims] 1. A two-independent sideband RF system with stereo-related intelligibility that appears as sideband modulation above and below the carrier wave.
A receiver for receiving an AM stereo signal, the receiver configured such that interference from adjacent channels is heard from far left and far right on a composite stereo audio output created from the receiver output. (a) The above model due to the above adjacent channel interference.
a device that receives an RF/AM stereo signal and converts the received RF signal into a corresponding intermediate frequency (IF) signal; (b) responds to the IF signal and demodulates this signal to a frequency of 5KHz or higher This device generates a pair of stereo output signals that are substantially separated from each other with respect to interference signal components of adjacent channels, and this device comprises: (1) demodulating the amplitude modulation component of the IF signal to
(2) means for generating a signal representing +R stereo information and having a bandwidth sufficient to include the adjacent channel interference component; (2) demodulating the phase modulation component of the IF signal to generate the L signal;
- means for creating a signal representing R stereo information and having a bandwidth sufficient to include the adjacent channel interference component; (3) combining the L+R signal and the LR signal;
A receiver comprising means for producing a pair of L and R stereo output signals, and (c) a device for separately providing the stereo output signals to a stereo audio output system.