JPS5850461B2 - Amplitude modulation stereo signal receiver - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of the Invention] The present invention relates to a receiver circuit capable of operating in both stereo signal reception mode and monophonic mode and automatically switching between these modes. It is.

[Description of prior art]

US Pat. No. 3,218,393 to the present inventor includes:
with a difference stereo signal (channel A signal minus channel B signal) that phase modulates the carrier wave and a sum stereo signal (channel A signal plus channel B signal) that envelope modulates the carrier wave. A receiver of the type comprising compatible stereo signal AM transmission and reception utilizing upper and lower sidebands associated with a stereo signal for stereoacoustic reception of a carrier wave thus modulated. is shown with.

A more detailed description of this compatible AM stereoacoustic modulation technique can be found in "IEEE Transaction on Broadcasting," published June 1971.
ng'' VOl, BCl2, /I6.2, pages 50-55, by the present inventor entitled ``Stereo Adapter System for Amplitude Modulated Broadcasting Station''.

The contents of US Pat. No. 3,218,393 will be explained below to the extent necessary as a basis for understanding the present invention with reference to FIGS. 4 to 9.

Figures 4 through 9 are each from U.S. Patent No. 321,839.
This corresponds to Figures 1 to 6 of No. 3.

In conclusion, if the configuration shown in Figures 4 and 5 is used and the modulation described below is performed, one of the two stereo signals can be distinguished in terms of stereo sound. substantially most of the stereophonically distinguishable components of the stereo signal appear in the primary sideband of one of the primary upper and lower sidebands of the carrier wave; This means that the carrier wave can be modulated by two audio signals that are stereoscopically related to each other such that the carrier wave appears in the other primary sideband.

In FIG. 4, two audio signals A and B (e.g. left signal and right signal) are stereo-related to each other.
is the stereo adapter S whose details are shown in Figure 5.
A, and the output signal P from this stereo adapter
The MS and AMS are fed into a standard AM transmitter SAMT.

The transmitter SAMT includes a low level class C amplifier LLAMP-1, a modulated amplifier MDAMP, connected as shown.
Low level audio amplifier LLAMP-2, modulator MD,
It has a linear amplifier LAMP and an antenna ANTN provided as necessary.

Stereo adapter SA has a configuration as shown in FIG.

The input signals A and B are supplied to the sum generating circuit SUM-1 and also to the difference generating circuit SUB, where the signal B
is passed through a phase inversion switch PR8W which may be provided as required.

The sum signal A+B from the sum generation circuit SUMI and the difference signal AB from the difference generation circuit SUB are supplied to the +45° phase shift circuit ps-i and the -45° phase shift circuit PS-2, respectively.
After all, the sum signal A+B and the difference signal A-B are in a perpendicular relationship.

This orthogonal relationship is important as will be understood from the explanation of FIGS. 6 to 9 later.

The output signal AMS from the phase shift circuit PS-2 is directly supplied to the transmitter SAMT as a signal used in the amplitude modulation system in the transmitter SAMT shown in FIG.

The output signal from the phase shift circuit PSI is sent to the balance modulator BM.
D, which modulator BMD also receives the output from oscillator O8C.

A part of the output from the oscillator O8C is sent to the phase shift circuit PS.
-3 to the linear summing circuit SUM-2, which receives the suppressed carrier output from the balance modulator BMD.

In the adder circuit SUM2, a quadrature modulated wave is obtained from the suppressed carrier wave output from the balance modulator BMD and the 90° phase-shifted carrier wave from the phase shift circuit PS-3, which is converted into signal radiation in the frequency multiplier FM. Multiplied to the desired frequency.

The output PMS from this frequency multiplier FM is supplied as a phase modulated carrier wave to the transmitter SAMT of FIG.

Components in Figure 5 BMD, 08Cj PS-3, SUM
-2, FM acts as a type of phase modulation carrier generator, but other known phase modulation carrier generators may be used in this part.

The transmitter SAMT in Fig. 4 is a phase modulated carrier wave PMS.
It acts to amplitude modulate the signal AMS (related to A-B) with the signal AMS (related to A+H).

Figures 6 to 8 show an extremely simplified analysis of the signal phase of the modulation technique used here. If A is eliminated and an input B of the same magnitude as the input A in the case of Figure 6 is added, Figure 8 has the same magnitude of input A as in the case of Figure 6 and the same as the case of Figure 7. The case is shown in which a magnitude input B (that is, A=B7''0 expressed in the formula) is added.

Also, 6-A in Figure 6, 7-A in Figure 7, 8- in Figure 8
A indicates the phase modulation component, 6-B, 7-B, 8
-B indicates the amplitude modulation component; 6-C, 7-C, and 8-C indicate the process of combining the phase modulation component and the amplitude modulation component;
-D.

γ-D, 8-D shows the results of such a synthesis.

Note that in obtaining Figures 6 to 8, it is assumed that the modulation in the transmitter is selected such that the secondary sideband component is much lower than the carrier wave and only the primary sideband needs to be considered. (For example, consider the case where inputs A and B are small.

Figure 6 shows a single tone (for example, 1000) without input B.
Hertz) is added as input A.

Under this condition it is ABA. Assuming that the phase modulated upper sideband component from input A is expressed as PMUSB/A, and the phase modulated lower sideband component from input A is expressed as PMLSB/A, 6-
In A, the relationship to these carrier waves C is shown by a solid line vector.

As a characteristic of phase modulation, the vectorial sum of the upper sideband component PMUSB/A and the lower sideband component PMLSB/A is perpendicular to the vector C of the carrier wave.

6-B is the amplitude modulated upper sideband component AMUS from input A.
Amplitude modulated lower sideband component AMLSB from B/A and input A
The relationship of /A to the carrier wave is shown by the dashed vector.

AMUSB/A and AMLSB/A as characteristics of amplitude modulation
The sum of the vectors added is in phase with the carrier wave vector C.

Namely, phase modulator BMD, O8C. PS-3,SU
The sum of the modulated waves in M-2, FM is the amplitude modulator MD, M
The phase is shifted by 90° with respect to the sum of modulated waves in the DAMP, in other words, the two are in a right-angled relationship.

, if the signal to the phase modulator and the signal to the amplitude modulator are in a quadrature relationship with each other as described above, when both modulations are combined, the signal will move counterclockwise as shown in 6-C. The rotating components PMUSB/A and AMUSB/A cancel each other out, and the clockwise rotating components PMLSB/A and AMLSB
The two developed a mutually reinforcing relationship, and in the end, PMLSB/A and A
Only the lower sideband signal component corresponding to the sum with MLSB/A will appear.

In the case of Fig. 7, the PML is
SB/B and AMLSB/B cancel each other out, and in the end, PM
Only the upper sideband signal valve corresponding to the sum of USB/B and AMUSB/B will appear.

Figure 8 corresponds to the combination of the cases in Figures 6 and 7, and the broken line vectors in 8-B, 8-C, and 8-D correspond to the corresponding parts in Figures 6 and 7. Part 2 of
It will be twice the size.

If the frequencies of inputs A and B are changed and Figures 6 and 7 are represented as a spectrum diagram, the result will be as shown in Figure 9, where the component of one stereo signal A is a single lower sideband. The component of the other stereo signal B appears only in a single upper sideband.

Considering inputs A and B at a selected moment,
The resulting modulated signal may be (1) composed of components that appear with the same magnitude in both the upper and lower sidebands (i.e., when A=B, "0"); (11) the upper and lower sidebands and Does it consist of sideband components of only one of the lower sidebands (i.e., B7'0 in A-0 or B=O?
A10), or if the component appearing in one of the upper and lower sidebands consists of a component whose magnitude is different from the magnitude of the component appearing in the other (i.e. A10,
B10 and A/B).

In the case of (1) above, when the obtained signal is received, it is not possible to obtain a signal component that can distinguish whether it is stereo sound or not.

On the other hand, in the case of (11), when the listener receives the obtained signal, it is possible to distinguish it as a stereo sound. "components that are stereophonically distinguishable."

In addition, the stereo information in the carrier wave has a hearing frequency of approximately 200Hz~
It exists in a frequency range of 5000 Hz, and since frequencies in this range transmit information that is "stereo-distinguishable", in this invention this is originally referred to as "stereo-distinguishable"; however, In particular, when the term "stereophonically distinguishable components" is used, it is used in the above-mentioned meaning.

Of course, a practical stereo input signal is spectrally extremely complex and complex, but the explanations given with respect to FIGS. 6-9 are helpful in understanding the basics.

Incidentally, when transmitting using the method shown in Figures 4 and 5, prepare two standard receivers and use one receiver as A in the spectrum diagram in Figure 9. You can enjoy stereo broadcasting by tuning to a frequency that is slightly detuned toward the part indicated by B, and tuning the other receiver to a frequency that is slightly detuned toward the part indicated by B. can.

As will become clear from the following description, the present invention relates to a stereo receiver equipped with a device that makes it possible to distinguish between the presence and absence of a stereo signal in the signal from the transmitter. On the receiver side, it is preferable to receive in stereo mode when a stereo signal is present, and receive in monophonic mode when a stereo signal is not present, and for this purpose the receiver state is automatically switched between both modes. It is.

To more fully understand the method of stereoacoustic modulation characteristics of the present invention, as will be explained in more detail below, reference is made to the inventors concerned with similar techniques for compatible single sideband modulation. Reference may be made to U.S. Pat. No. 3,350,645, which discloses a secondary sideband that allows a single sideband modulated signal to be compatibly received by a common envelope detection receiver. Signal splitting (sign
splitting), phase shifting, doubling the frequency of a split signal, and signal combining.

Reference is now made to FIGS. 10 and 11 to the extent necessary as a basis for an understanding of the present invention.
The contents of No. 0645 will be explained.

In conclusion, if a transmitter with the configuration shown in Figure 10 is used and the modulation described below is performed, the main component whose phase is shifted but whose frequency is the same as the fundamental wave A compatible single sideband (75%) and a compatible single sideband (75%) and the remaining part includes the second harmonic base.
SB) method can be obtained.

Compatible single sideband system means that it can be received by either a monophonic mode receiver or a stereo mode receiver; in the case of stereo, each of the two stereo signals can be received in the upper and lower sidebands. In other words, taking into consideration that the signal is transmitted using only one sideband of the waveband, reception can be performed with either a double sideband receiver or a single sideband receiver.

A wave that is compatible with a compatible single sideband scheme is one that consists of a somewhat reduced carrier wave, a primary sideband component, and a significantly smaller number of secondary sideband components.

FIG. 11 shows a signal waveform at a point with a corresponding symbol in FIG. 10.

In FIG. 10, a signal obtained from an appropriate audio frequency signal source AFS such as a microphone is passed through a low-pass filter LP that acts to limit the signal to signals in the frequency band assigned to the device.
F and its output (FIG. 11a) is passed to a wideband phase shift circuit WBPS, which converts the three audio frequency output components, namely the non-phase shifted component (( θ + 00) (see Figure 11), a component given a 45° phase shift (denoted as (θ + 45°)) (Fig. 11 2), -45°
component which is given a phase shift of (θ−45
) (shown in Figure 11) is produced.

The (θ+45°) component and the (θ−45°) component are in a right-angled relationship, which is important for producing a wave suitable for the single sideband system.

The component at (θ+0°) is passed to the full-wave rectifier circuit FWR in the wideband frequency doubler WBFD, and its output (FIG. 11E) is passed to the nonlinear circuit NLN in the frequency doubler WBFD.

The frequency doubler WBFD is designed such that its output (see FIG. 11) consists essentially only of the second harmonic of the (θ100) component.

The frequency doubled audio frequency output from the frequency doubler WBFD is supplied to the summing circuit SUM via a suitable potentiometer, while the summing circuit SUM is supplied with a signal from the phase shift circuit WBPS via a suitable potentiometer. The component at (θ+45°) is also supplied.

The output from the summing circuit SUM (FIG. 11G) is a complex audio frequency signal that approximately approximates the desired phase modulation characteristics required for compatible single sideband schemes.

This composite audio frequency is fed via a variable delay circuit TD to a phase modulator PMD and is used to phase modulate the carrier wave from oscillator O8C.

The output of this phase modulator PMD is amplified by a high frequency amplifier RFA and becomes a phase modulated high frequency signal (FIG. 11H).

On the other hand, the (θ-45°) component is transmitted to the amplitude modulator AMM via the audio amplifier AFA and a suitable potentiometer.
A power amplifier PAMP is used to amplitude-modulate the phase-modulated high-frequency signal, and the output of this power amplifier PAMP (11th diagram) is supplied to the antenna AN
TN is supplied.

It should be noted that, in order to make it easier to understand, the horizontal axis direction is greatly exaggerated in FIG. 11 E, especially in FIG.

The configuration shown in Figure 10 results in a signal whose frequency is doubled for the (θ + 0°) component and a signal (θ + 45°) whose frequency is doubled.
The signal whose carrier wave is phase-modulated by the sum of the components of (θ+45
), and the resulting signal is suitable for a single sideband (SSB) system and can be received compatiblely with an ordinary envelope detection receiver.

Note that the configuration shown in Fig. 10 is related to a single sideband communication method using the upper sideband, but changing to the single sideband method using the lower sideband simply requires the (θ+45°) component. By simply reversing the connections between the points where the and (θ-45°) components are output, in other words, the (θ-45°) component is used for phase modulation, and the (θ+45°) component is used for amplitude modulation. It will be understood that this can be achieved by using

In addition to the above, various stereophonic (stereo) transmission and reception methods have been proposed, and although they are not particularly necessary for understanding the present invention, they are useful for understanding the basics, so we will refer to them here. In other words, both stereo-related signals are the FM band carrier and the AM band carrier, respectively.
No. 3,009,151 to 5hoaf showing a two-channel FM-AM stereo system adapted to perform frequency and amplitude modulation on a band carrier, single-channel AM stereo using a synchronous detector in the receiver section of the system. U.S. Pat. US Patent No. 3
No. 068,475, U.S. Pat.
AM in which each of these carrier waves is amplitude modulated with both signals that are stereoscopically related to each other.
There is US Pat. No. 3,231,672 to Colins which shows a stereo system.

[Features and objects of the present invention]

An inherent advantage and feature of the stereo signal reception scheme according to the invention is that it uses modulation at a very low frequency to indicate to the receiver the presence of a stereo signal and that this signal and indication can It is intended to be used for automatic switching of reception modes from that point on, and/or for providing carrier tuning indication means.

Another feature of the invention is the use of a single fixedly tuned intermediate frequency channel in the receiver, increasing efficiency and accuracy.

Furthermore, an important feature of the present invention is the AM stereo signal reception system, which uses a common AM envelope detection type receiver to receive signals in a monophonic mode using one AM envelope detection type receiver. The reception can be performed without distortion, or in stereo according to the nature of the transmitted signal, using two common AM envelope detection receivers, tuned slightly above and below the carrier frequency, respectively. It is an object of the present invention to provide a fully compatible AM stereo signal reception scheme in the sense that it can be received either in signal reception mode or in monophonic mode.

[Description of embodiments with drawings]

The present invention will be described below with reference to the drawings.

FIG. 1 shows a transmitter used in conjunction with the receiver of the present invention.

In this transmitter, commonly available stereoscopically related input signals R and R are applied to a difference generating circuit 10 and a sum generating circuit 12.

The sum output 14 is provided to a phase shift circuit 16 from which the output 18 is utilized as the audio frequency input to the amplitude modulation section of the associated AM transmitter.

Up to this point, the evolution of the AM modulation of the transmitted signal is the same as the AM modulation provided by the transmitter exciter or adapter shown in FIG. handle).

The stereo difference signal output 20 from the difference generation circuit 10 is used to generate a phase modulation component (i.e. a signal corresponding to the output PMS in FIG. 5) which is supplied to the phase modulator section of the transmitter.
is preferably fed to a low pass filter 22.

This low pass filter 22 suitably has a cutoff frequency of about 5 kilocycles because there is little stereo information above about 5 kilocycles.

In accordance with one aspect of the present invention, the output 24 of the low pass filter 22 is applied to the phase shift circuit 26 to advance the phase by 45 degrees (providing a 900 degree relationship with the audio signal 18 produced as the output from the phase shift circuit 16). and the output 24 from the low pass filter 22 is connected to a phase shift circuit 28.
(giving a relative phase shift of 0°).

The output 30 of this circuit 28 is in turn a broadband frequency doubler 3
2.

The output of the frequency doubler 32 is adjusted in amplitude as shown diagrammatically by an attenuator 34 and output from the phase shift circuit 26 to a signal combination (summing) circuit 38 to adjust the amplitude of the fundamental component input 40. Generates a human power signal 36 that is approximately 13%.

The relative amplitude of this input signal 360 second harmonic is chosen to minimize unwanted sidebands at 50% modulation depth.

The combined signal output 42 is then connected to a variable time delay circuit 44.
and phase modulates the carrier wave input from the high frequency crystal oscillator 45 in a phase modulator 46 , and the phase modulated wave from the phase modulator 46 is passed through a frequency multiplier 48 .

The output 50 from the frequency multiplier 48 is transmitted to the associated A in a manner similar to the phase modulated high frequency output PMS in the stereo adapter shown in FIGS.
It is used as a phase modulated carrier wave in the M transmitter.

The addition of the slight second-order high frequency component described above improves the compatibility of the transmitted signal with respect to ordinary envelope detection type receivers (makes the reconstructed signal correct in monophonic mode), and
This provides good stereo reception using two receivers that are tuned to frequencies slightly apart above and below the carrier frequency of the station and are physically spaced apart from each other.

Compared to the method of generating phase-modulated high frequency components in the manner shown in FIGS. 4 and 5, the method of generating phase-modulated components shown in FIG. 1 of the present application is fundamentally Differently, in this case it is concerned with shifting the phase of the audio frequency components and multiplying the frequency by a factor of two.

Also, the PM in the stereo transmitter exciter shown in FIG.
The generation mode of the M frequency component is the single-audio mode shown in Figure 9, in which the phase of the audio frequency component is shifted and the frequency is doubled to synthesize the phase modulated wave. It is similar to the method of generating a phase modulated component of a compatible single sideband signal from a frequency source.

However, in the case of Figure 1, the signals are generated from a pair of stereo-related audio input signals, and the combined phase modulated wave is specifically optimized to match the 50% modulation depth. , in other words, the output of the frequency doubler is adjusted to have an amplitude of about 13% with respect to the amplitude of the fundamental wave component.

Additional circuit portions may vary based on the particular needs and objectives of the present invention, as shown in the transmitter exciter shown in FIG. It involves modulating the transmitted signal with a very low frequency signal that acts as shown.

The term “very low frequency” signal refers to a signal with a frequency below the audible frequency range;
The first edition was published in 1962 by Howard W., Sams.
Published by E Co, Inc.”Moder
n Dictionary of Electronici
cs”.

This extremely low frequency signal can be used as an amplitude modulation signal of the AMM component output 18 or as an amplitude modulation signal of the PM component output 50.
and 500 can be used as both modulation signals.

In the first case, as shown in solid lines in FIG. 1, a 15-cycle oscillator 52 produces an output 54 which is combined with a phase-shifted sum output 18 having a variable amplitude defined by an attenuator 56.

When phase or frequency modulation of the very low frequency stereo signal presence indication signal is to be used simultaneously or alone with the very low frequency signal modulation power 54, this can be done through the use of a 15 cycle oscillator 58, which oscillator 5
The output from 8 is fed to a phase modulator 46 so that a very low frequency phase or frequency modulated signal appears at the phase modulated component high frequency output 50 .

In a typical transmitter exciter involving frequency modulation with a very low frequency signal, the low frequency oscillator 58 signal is a simple narrowband FM signal which may take the form of a variable capacitance circuit connected in parallel across a crystal oscillator. frequency modulated by a modulator,
An output frequency is generated that provides the receiver with a desired stereo signal presence indication signal having a very low frequency.

In the typical case where an AM stereo wave is frequency modulated over a total of 15 cycles and the degree of frequency deviation is made positive or negative by 25 cycles, the narrowband frequency modulation of this signal is essentially There is no effect on the signal bandwidth, and there is no audible impact on the listener to the AM receiver.

The modulation depth is kept low, typically about 5 to 10% in the case of carrier amplitude modulation, and typically less than a modulation index of 1 in the case of FM or PM modulation; Therefore, even if the receiver were to receive a very low frequency modulated signal, the receiver's audio system would produce a significant attenuation at 15 Hz, making this very low frequency signal virtually inaudible and therefore ineffective in practice. There is no negative effect on the sound heard.

As will be appreciated, the oscillators 52 and 58 are controlled in a known manner and as shown diagrammatically here by respective switches 53 and 59 to be brought into circuit during stereo signal transmission.

As previously mentioned, the indication of the presence of a stereo signal to the various receivers receiving the transmitted signal is in the form of a very low frequency amplitude modulated signal and/or a very low frequency frequency or phase modulated signal. Possibly, and if both modulations are used, an infrasonic signal of the same frequency or two infrasonic signals of different frequencies can be used as desired.

FIG. 2 shows, as one embodiment of the invention, a receiver specifically designed to receive AM stereo signals of the type produced by the transmitter exciter and associated AM transmitter shown in FIG. This shows one form of .

As shown in FIG.
Typical superhetero gain device configuration for the F) stage and intermediate frequency (IF) stage: antenna 60, variable radio frequency amplifier 62, variable high frequency oscillator 64, mixer 66
, and a combination 68 of a fixed frequency (eg, 455 kilocycles) intermediate frequency amplifier stage and intermediate frequency bandpass filter.

This receiver circuit utilizes an intermediate frequency bandpass filter with suitable selectivity characteristics, such as those commonly used in relatively high quality monophonic AM sets.

The output Cuff 0 from the intermediate frequency amplifier and filter 68 is provided to a fixed frequency upper sideband filter 72 and a fixed frequency lower sideband filter 74 as well as to a conventional double sideband detector 76.

This detector 76 is typically in the form of a diode detector.

The double sideband detector stage 76 and output cuff 8 are typically AGC
It is utilized for automatic gain control through an automatic gain control line shown at (80) and is supplied as a monophonic signal input 80 to electronic switches 82 and 84.

In the case of monophonic signal reception, electronic switches 82 and 84 provide monophonic signal power 80 to audio amplifiers 80 and 88 and respective loudspeakers 90 and 92 for conventional monophonic reception, as will be explained in more detail below. be carried out.

When receiving stereo signals by the receiver, the respective upper sideband filters 72 and lower sideband filters 74, which may take the form of ceramic filters, quartz filters, or common LC or transformer-coupled circuits, provide an intermediate frequency passband. The function is to separate the upper sideband and lower sideband of the signal appearing in the signal.

Filters 72 and 74 characteristically have fairly steep curves relative to the lower limit of upper sideband filter 72 and the upper limit of lower sideband filter 74.

These relatively steep cut-off characteristics, in addition to providing good stereo signal suppression, detect the slope of the very low frequency frequency modulation components generated by the transmitter when a stereo signal is being transmitted. It can be used for

In FIG. 2, a lower sideband filter is used to detect the slope of the very low frequency angular modulation.

The resulting very low frequency is passed through a 15Hz band filter 1.
04, this filter 104 supplies a signal to an NPN type voltage comparison gate circuit shown at 102.

The voltage comparison gate circuit 102 is also supplied with the DC voltage generated by the envelope detectors 94 and 96.

As can be seen, the 15 Hz bandpass filter 104 has its inputs either sideband detectors 94 and 96 or double sideband detector 7.
6, the filter 104
The 0 function is to separate and pass the 15 Hz stereo signal presence indication tone.

Two detectors 94 and 96 when the receiver is properly tuned and a stereo signal presence indication tone is present.
The DC voltages from are approximately equal and the comparison gate is suitably biased to pass this tone through coupling capacitor 106 and AC amplifier 108 to stereo signal present indicator SL, energizing this indicator.

When the receiver is not properly tuned, one of the detectors 94 and 96 will generate a larger DC voltage than the other, resulting in the comparison group 11020 sections not being equally biased and very low frequency tones. is completely or partially blocked.

Looking at the direct relationship between the voltage at output 110 and receiver tuning (expressed by the relative strength of the upper and lower sideband signals as they appear at detector outputs 98 and 100), The stereo signal presence indicator SL can be used as a tuning indicator and can be used to indicate the presence of a stereo signal.

In addition to the output of the comparison gate 102 being supplied to the stereo signal presence indicator SL through the AC amplifier 108, another output 112 is a low-pass filter consisting of a rectifier diode 114, a diode load resistor 115, and a filter capacitor 116. is applied to the circuit to generate a DC control signal input 118 to electronic switches 82 and 84.

As will be readily appreciated, the presence of a DC control signal at input 118 changes the control state of electronic switches 82 and 84 to bring the switch outputs into contact with monophonic input 80 to amplifiers 86 and 88 in a known manner. and brings the switch output into contact with the stereo inputs 98 and 100 so that when the control signal input 118 is present, the respective amplifiers 86 and 88 are connected to the upper sideband detector 94 and the lower sideband detector. Receives input from 96.

The RC filter circuits 105 and 101 of the voltage comparison gate 102 have time constants large enough to effectively attenuate the very low frequency stereo signal presence indication tone and any other low frequency audio components present in a known manner. is given.

In this way, filter circuits 105 and 107 have 15
Filter 1 to pass the tone indicating the presence of a stereo signal in Hz
04 and opposing transistors 109 and 111 of gate 102.

When either transistors 109 and 111 are biased in the blocked state, very low frequency tones are blocked from reaching amplifier 108.

As will be readily understood, gate 10 to amplifier 108
The amplitude of the output of 2 is the DC component of the applied voltage (detector output 98
and 100), maximum output occurs when these DC components are equal, and there is no output when the receiver is not properly tuned and one or both portions of gate 1020 are non-conducting.

FIG. 3 shows, partially in block form, a modification of the receiver according to the invention.

In this example, the same reference numerals are used to designate the same circuit elements; in this modification, the intermediate frequency amplifier 68', which need not include a bandpass filter stage, passes its output 10 to the upper sideband filter 72 and the lower sideband filter stage. These filters γ2 and 14 supply signals to respective detectors 94 and 96 and inputs 120 and 122 to a summing circuit 124, which
The output from 4 is passed through an intermediate frequency amplifier 126 to a double sideband detector 16 which supplies its output to an automatic gain control line 8o in the manner shown in FIG. Another output γ8 is provided to monophonic inputs 8o of electronic switches 82 and 84.

The key difference in this modified receiver circuit when compared to the configuration shown in FIG. 2 (which is otherwise identical to that of FIG. 2) is that the intermediate frequency channel or otherwise AM without providing separate selectivity to both sideband parts of the system.
The selectivity is obtained solely from the upper sideband filter 72 and the lower sideband filter γ4.

Removal of one filter from the circuit is advantageous for integrated circuit applications of the receiver circuit.

In employing this modified selectivity, upper sideband filter 72 and lower sideband filter 14 preferably have a phase relationship at the carrier frequency such that the carrier level is not attenuated relative to the level of each sideband. configured to provide an amplitude relationship.

For a flat response, the carrier crossover point should fall about 6 decibels below and the two filters should be in phase at the intersection.

It is desirable to provide a carrier boost, i.e., to design the filter to be, for example, 3 dB below the intersection point, which improves the performance of the receiver in terms of minimizing the effects of selective carrier fading. Make it slightly better.

In such a case, a listener in monophonic mode could enjoy slightly improved fading characteristics and possibly a slight bass boost.

If this cold boost is not considered desired,
It can be eliminated in the receiver, such as by providing a suitable audio coupling circuit between the double sideband detector and the electronic switch circuit.

As will be understood by those skilled in the art, the voltage difference between the DC components of detectors 94 and 96 may also be utilized for automatic frequency control purposes in known manner, if desired.

As described above, according to the present invention, there is provided a means for extracting a signal indicating whether or not a currently transmitted signal is a stereo signal from a received signal, and a means for extracting a signal indicating whether or not a currently transmitted signal is a stereo signal, and a visual indicator for indicating the presence of a stereo Since the stereo presence indication signal can be used to give a visual indication to the visual indicator indicating the presence of a stereo signal, it can also be used as a tuning indicator of the receiver. .

In addition, by providing a device for controlling the audio signal output channel, the receiver can automatically switch between the stereo reception mode and the moiphonic reception mode using the stereo presence indication signal, always adapting to the nature of the transmitted signal. It is possible to receive

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a transmitter used in conjunction with the receiver of the present invention, FIG. 2 is a block diagram showing a specific example of the receiver according to the present invention, and FIG. 3 is a block diagram of a transmitter used in conjunction with the receiver of the present invention. Figure 4 is a block diagram showing the configuration of the transmitter that is useful for understanding the basics of the transmitter shown in Figure 1. Figure 5 is a diagram showing a modification of the stereo adapter used in Figure 4. The detailed block diagrams shown in FIGS. 6, 7, 8, and 9 are diagrams that help explain what kind of transmission signals can be obtained by the configurations in FIGS. 4 and 5. Figure 10 is a block diagram showing another configuration of the transmitter useful for understanding the basics of the transmitter shown in Figure 1, and Figure 11 is a diagram showing signal waveforms appearing at several points in Figure 10. . 10: Difference generation circuit, 12: Sum generation circuit, 16: Phase shift circuit, 22: Low-pass filter, 26°28 two-phase shift circuit, 32: Frequency doubler, 38: Signal combination circuit, 44
: variable time delay circuit, 45: high frequency crystal oscillator, 46:
Phase modulator, 48: Frequency multiplier, 52: 15 cycle oscillator, 56: Attenuator, 58: 15 cycle oscillator,
62: variable radio frequency amplifier, 64: variable high frequency oscillator,
66: mixer, 68: intermediate frequency amplifier and bandpass filter, γ2: upper sideband filter, 74: lower sideband filter, 76: double sideband detector, 82° 84: electronic switch,
86.88: Audio frequency amplifier, 90,92: Loudspeaker, 9
4, 96: Envelope detector, 104: Bandpass filter, 10
8: AC amplifier.

Claims (1)

[Scope of Claims] 1. Most of the stereophonically distinguishable components of one of two stereophonically related audio signals are located in the first-order upper sideband and the first-order lower sideband of a carrier wave. The carriers are stereo-related to each other such that a majority of the stereophonically distinguishable components of one of the sidebands appear in the primary sideband of the other signal and appear in the other primary sideband. a stereo radio receiver for receiving a signal modulated with two audio frequency signals, and further modulated at a low level with an infrasonic signal available at the receiver to indicate the presence of a stereo signal. a superheterodyne device that produces an intermediate frequency signal, including an intermediate frequency bandpass device that passes both the upper and lower sidebands of the received signal, and an upper and lower sideband output at a frequency of the intermediate frequency; a separate amplitude modulation detector for each of the upper sideband output, the lower sideband output and the output obtained through the intermediate frequency bandpass device; apparatus for receiving an input from one of the outputs of these detectors and separating said infrasound signal therefrom; and means for providing said separated infrasound signal to a visual indicator for stereo presence indication. A stereo wireless receiver comprising: 2 The majority of the stereophonically distinguishable components of one of two stereophonically related audio signals are located within the primary upper and lower sidebands of the carrier wave. Two audio frequencies whose carrier waves are stereo-related to each other such that the primary sideband of one signal appears in the stereophonic sideband and most of the stereophonically distinguishable components of the other signal appear in the primary sideband of the other signal. A stereo radio receiver for use in conjunction with a transmitter having a device for modulating a signal and a device for modulating said carrier wave with an infrasonic signal at a relatively low modulation level, said stereo radio receiver being at a frequency of an intermediate frequency. an apparatus for separately producing an upper sideband output and a lower sideband output; and an amplitude modulation detector for separately detecting the upper sideband output and the lower sideband output to produce a pair of stereo signals; a device for comparing direct current components of the detected stereo signals; a device for separating the very low frequency signals; and a device for separating the separated very low frequency signals when the direct current components of the compared stereo signals are substantially equal. a device for transmitting signals to a visual indicator to cause the visual indicator to indicate the presence of a stereo signal;
a device for controlling the audio signal output channels of the receiver so as to apply stereoscopically related audio signal inputs corresponding to the outputs of the presence indicating device to the audio signal output channels of the receiver; A stereo wireless receiver comprising: