JPS637065B2 - - Google Patents

Description

[Detailed Description of the Invention] This invention was previously applied to Japanese Patent Application No. 36-4778 and Japanese Patent Application No. 50-50 filed by the same inventor as the present inventor.
The present invention relates to an AM stereo receiver designed for the reception of carrier waves having stereo-related information appearing in each of the upper and lower sidebands of the transmitted signal, as described in US Pat. No. 83348.

An AM stereo receiver according to the invention provides carrier enhancement to reduce signal distortion at low levels of received signal strength and/or inverse amplitude modulation of the carrier to obtain a stereo difference (L-R) signal. and/or perform quadrature demodulation of the received carrier and use in-phase detection (e.g. envelope detection or product demodulation) to obtain stereo sum (L+R) signal information, relative to each other in a manner known per se. Stereo related (L and R) outputs are generated by phase shifting and a combination of both stereo sum and stereo difference signals. Modulation of a carrier wave with a subaudible frequency (eg 15 Hz) is advantageously used to indicate the presence of a stereo modulated signal at a receiver. Aspects of the invention also relate to specialized receiver circuitry with stereophonic and monophonic capabilities and automatic switching between them.

related to stereo-related upper and lower sidebands, phase modulating the carrier with difference stereo signal (L-R) information and envelope modulating the carrier with sum stereo signal (L+R) information;
Compatible stereophonic AM transmission and reception is described in Japanese Patent Application No. 36-4778, along with some type of receiver for stereophonic reception of carrier waves so modulated. A more detailed discussion of this compatible AM stereophonic modulation technique can be found in IEEE Transactions on
Broadcursing's BX-Volume 17 No. 2, 1971
June issue (IEEE Transactions on
Broadcasting, Vo1.BX-17, No.2, June1971)
"A Stereophonic System For Amplitude Modulation Broadcasting Stations" on pages 50-55 of
Amplitude Modulated Broadcast Stations)'' by the inventor. The contents of the aforementioned patents and articles are incorporated herein to the extent pertinent.

Barton's US Patent No.
Also known is a so-called "compatible" stereophonic AM system, described in US Pat. No. 3,102,167, which utilizes a compromise quadrature modulation technique in practice. To reduce monophonic distortion, the Burton method uses ±
The relative phase angle between the carrier and sidebands of 25° to 30° is utilized to generate a two-channel signal through the use of a phase-shifted enhanced carrier and product demodulation; No combination of signals was performed.

Also, Shoaf's US patent number related to the two-channel FM-AM stereo system.
A stereophonic sound transmission/reception method such as that described in No. 3009151 is also known, but with this method, stereo-related signals are
Frequency modulation and amplitude modulation are performed for the FM band and AM band carrier waves, respectively. U.S. Pat. No. 3,068,475 to Avins discloses a stereo transmit and receive system in which one stereo-related signal is amplitude modulated about one carrier and another stereo-related signal is frequency modulated about the same carrier; ) Other U.S. Pat. No. 3,167,614 discloses the use of a sub-audible signal tone to indicate the presence of a stereo signal in an AM/PM type transmission system, and U.S. Pat. No. 3,231,672 to Collins discloses the same An AM stereo system is disclosed in which carrier waves having different frequencies but different phases are amplitude-modulated with stereo-related signals and are linearly added.

The features and advantages of the invention are realized by the presentation of AM stereo receivers of various types for the reception of radiated energy carriers modulated with two stereo related signals (L and R), but in this case Each signal is essentially a stereo sum (L
+R) information and phase modulation of the carrier wave with essentially stereo difference (L-R) information, which appears in an independent first-order single sideband, and the receiver Stereo difference of signal (L
-R) Incorporating the use of quadrature demodulation of the phase modulation to represent the information and incorporating one or more of the following techniques to optimize the quality of the output stereo signal.

(1) The use of inverse amplitude modulation of the carrier, i.e., the use of an envelope to additively and inversely modulate the received carrier so as to reduce the distortion of the stereo difference signal derived from the additively modulated carrier. ) use of the fundamental wave (and one or more harmonics of the chosen form).

(2) The stereo difference signal derived from the carrier is enhanced so that there is essentially no phase modulation distortion associated with the carrier burst and even when the received carrier is fully (i.e., 100%) modulated. Carrier augmentation, ie, the use of an enhanced carrier, preferably with control such as a phase-locked loop on the carrier boost input so that the carrier does not contain noise bursts.

(3) Apparatus, in connection with any of the foregoing techniques, that detects and utilizes a subaudible (e.g., 15 Hz) signal tone modulated on a received carrier as an indication of the presence of a stereo signal; (It is desirable to use it to automatically control the machine output method).

Another feature and advantage of the invention arises from the avoidance of the use of circuit components such as sideband filters in the receiver of the invention, thereby readily allowing for the employment of integrated circuits.

Yet another advantage and feature of the AM stereophonic transmission and reception system of the present invention is that it selectively modulates the carrier wave with subaudible frequency tones to indicate the presence of a stereo signal at the receiver, which signal is stereophonic and It can be used to automatically switch between monophonic reception systems and to provide a carrier tuning indicator.

Other features and advantages of the invention will become apparent from the following description and discussion of certain representative embodiments of the invention.

FIG. 1 is a block diagram illustrating a typical compatible AM stereo receiver according to the present invention. Antenna 10 is connected on line 12 to a conventional RF/IF superheterodyne circuit 14 which produces an intermediate frequency output 16, a portion of which is connected to an envelope detector 18 (which includes A common mode detection device such as a common diode detection circuit is suitable). IF output 16
is also supplied to a carrier track filter circuit 20, such as a phase-locked loop device, for carrier selection without inducing phase distortion, such as the IC No. It can be something conventional in itself, such as the circuit that can be obtained by using a .562.

The output 22 of the carrier track circuit 20 is representative of the carrier portion of the received carrier (received stereo signal) and is fed to a summing circuit 24 where it is added to the received carrier (at the IF), but not from the RF/IF stage 14. A portion of the output 16 of also serves as an input to the summing circuit 24. Addition circuit 2
The combined output 26 from 4 is advantageously such that the enhanced carrier is about half as large as the received carrier, i.e., 0.9415 volts in the particular case shown, as shown in the representative example of FIG. relative to the relative carrier level in the signal
Contains a carrier wave elevated to have a relative voltage of 1.5 volts.

This phase modulated and enhanced carrier output is
Since the multiplied carrier cannot have instantaneous zero amplitude, i.e., 100% modulation negative or negative, its phase modulation (as discussed in more detail below, it can be reversely amplitude modulated in amplitude modulator 28) It is more suitable for demodulation to obtain the following data.

The carrier track circuit output 22 is also provided to a transfer network 30 which shifts the carrier phase by +90 degrees, and the network 30 in turn provides the transferred carrier output 32 to a product demodulator 34. Collectively, network 30 and demodulator 34 constitute what is collectively designated 36 and is known as a quadrature demodulator. The transport network 30 is described in "Radio Engineer's Handbook", edited by Keith Henney, 5th edition, Chapter 12, pages 16-52 ("Radio
Engineer Handbook”, edited by Keith
Henny, 5th Ed.Mc Graw‐Hill Company;
New York, 1959, at Chapter 12, and also at
Suitable are those in their usual format, such as those shown on pages 16-52). The product demodulator 34 is also suitably of a per se conventional type, such as is known, for example, for IC No. MC1596L manufactured by Motorola.

The output 38 of the common mode detector 18 is the amplitude modulation envelope of the received carrier, and more particularly, as is known per se, the amplitude modulation or envelope in this type of AM stereo transmission is the sidewave of the received carrier. Output 38 is the fundamental of such an envelope, since it is an essentially undistorted reproduction of the stereo sum (L+R) information in the band. This envelope fundamental output 38 is provided to an amplifier 40, the amplified output 42 is applied to a summing circuit 44, which in turn amplitude modulates the phase modulated and enhanced carrier (output 26) in an amplitude modulator 28. An audible modulation input 46 is provided for. Amplitude modulator 28
The output 48, which may be termed an inverse amplitude modulated phase modulated enhanced carrier, is utilized as the second input to the product demodulator 34 in the quadrature demodulation circuit 36.

An important feature of the invention is that the amplitude modulator 28
The additional amplitude modulation applied to the carrier at 2 significantly reduces the distortion that would otherwise appear at the output 50 of the quadrature demodulator 36. Envelope fundamental wave (output 3
8) as the only input to the amplitude modulator 28 (such mode of operation is achieved by opening the manual switch 52), the distortion at the demodulated output 50 is equal to the voltage The ratio decreases to about 4%. If further reduction of harmonic distortion in the stereo difference (L-R) signal is desired or necessary, frequency doubler 54 can be brought into circuit by closing switch 52. In this mode of operation, the second harmonic output 56 from the frequency doubler 54 is combined with the envelope fundamental (output 42) by the summing circuit 44.
are combined to provide the fundamental and harmonic envelope components to the audio input 46 to the amplitude modulator 28, resulting in further reduction of distortion. The approximate relative best level of amplitude modulation in amplitude modulator 28 is approximately 26% of the total modulation voltage in voltage ratio for fundamental modulation and approximately 8% for second harmonic modulation. These inverse amplitude modulation levels cause the output 50 from quadrature demodulator 36 to
The total strain of second order or higher that appears in the voltage ratio is
Decrease to 0.8%.

A phase-shifting network arrangement known per se converts the stereo difference (L-R) signal output 50 into an envelope fundamental (L+R).
It is used in combination with output 38 to provide relatively undistorted stereo-related signals (L and R) in a manner known per se and explained in more detail below.

The receiving device shown in FIG. 1 indicates the presence of a stereo signal in response to subaudible signal tone modulation of a carrier wave;
and preferably to automatically establish and maintain the receiver output in stereo when such a stereo presence signal is present. Automatic switching of receiver output formats is accomplished by control of electronic switch 58, as will be explained in more detail below. When electronic switch 58 closes, demodulator output 50 is connected to the .theta.-45 DEG transfer network 60 from which output 62 is applied to summing circuit 64 and subtracting circuit 66. The stereo sum (L+R) signal appearing as detector output 38 is similarly applied to its associated θ+45° transfer network 68, and the output 70 therefrom is also applied to sum and difference circuits 64,66. As shown, transfer networks 60 and 68 are phase shift network pairs (θ-45° and θ+45°), which are well known per se in the art and which provide a relatively constant signal amplitude. provides a relatively constant relative phase difference of essentially 90° over the effective audio frequency range while maintaining .
Generally, in this type of output circuit, the summing circuit 64 favors the left or L channel stereo information so that the L speaker 68 is driven by the L stereo signal, as well as the subtracting circuit 66.
affects the right or R channel stereo information to drive the R speaker 70. Also, of course, as is known per se, stereophonically indistinguishable information in the received signal sidebands (i.e.
The monophonic information (monophonic information) appears simply as two primary sidebands on the received carrier, i.e., as a conventional dual-sideband amplitude modulation, and as part of the detection envelope to make the L loudspeaker 68 and the R loudspeaker 70 monophonic. drive

Electronic switch 58 is controlled by a subaudible tone (eg, 15 hertz) that appears as a modulation in the carrier of the received signal. Assuming that the subaudible signal is transmitted by amplitude modulation of a carrier wave (which is currently considered to be the preferred method of modulation), switch 72 in FIG. Illustrated in the correct position to respond to the sound indication, the sub-audible envelope component appearing at the detector output 38 is connected to the switch 7.
2 to a bandpass filter 74 and thence provides an isolated sub-audible signal output 76 to an amplifier 78 whose output 80 illuminates a stereo presence indicator light 82. The subaudible tone output 80 is also applied to a detector 84, which activates the electronic switch 58 by closing the switch when the stereo subaudible tone is present.
A direct current component is generated at output 86 that acts to control the output. Another method of operation that can be used is in which the sub-audible signal tone indicating the presence of a stereo signal is phase modulated on the carrier wave (see patent application No.
50-83348).

In this mode of operation, the quadrature demodulator 36 of the receiver shown in FIG. The demodulator output 50 is then sent to a bandpass filter 74, and the filter output 76 controls a stereo display 82 and electronic switch 58 in a manner similar to that described above.

It should be noted that if phase modulation or the like (e.g., quadrature modulation) is used to modulate the subaudible signal on the carrier, the carrier track circuit 20 will its output 2 so as not to maintain track
2 must be sufficiently narrow. If such a track were to be maintained, the sub-audible signal would be significantly attenuated and the stereo response circuitry (eg, electronic switch 58) would be inoperable. Also shown in FIG. 1 is a manual switch 88 which is closed when the receiver is to be used exclusively for stereo reception. In this mode of operation with switch 88 closed, switch 88 provides a direct interconnection between product demodulator output 50 and its associated phase shift network 60, so that switch 72, bandpass filter 74, and amplifier 7
8, stereo lamp 82, detector 84 and electronic switch 58 are unnecessary.

FIG. 2 shows a portion of an alternative AM stereo receiver according to the invention in which the receiver is shown in FIG. 1 except as shown in FIG. 2 and discussed below. It is similar to what was done. As shown in Figure 2, this alternative circuit
Two amplitude modulators 28' and 28'' are used in place of the single modulator 28 shown. An amplifier 40 receives as its input the detector output 38 and for the first amplitude modulator 28' ( (as in Figure 1)
A fundamental wave component input 42 is provided. In this alternative circuit, the output of the first amplitude modulator 28' is an input 90 to the second amplitude modulator 28'', and another audible input 92 to the amplitude modulator 28'' is taken from the frequency doubler 54. It can be done. Second amplitude modulator 2
The output 94 of 8" is then used as an input to the product demodulator 34. This configuration requires a second amplitude modulator 28", but somewhat less than the circuit configuration shown in FIG. give strain.

FIG. 3 shows a further alternative inverse modulation circuit that reduces distortion in the demodulated stereo difference signal output to even less than that of the configuration shown in FIG. In the circuit of Figure 3,
The output 42 from amplifier 40 is applied to a frequency doubler 54 (as in FIG. 1), which in turn feeds a second frequency doubler 54 (also as in FIG. 1) to a summing circuit 44'. A harmonic output 56 is provided. As can be seen, the operation of frequency doubler output 56 in combination with fundamental output 42 in amplifier 40, frequency doubler 54 and summing circuit 44' is controlled by switch 52 in the circuit of FIG.
It is the same as when the is closed. However, the third
In the figure, another envelope fundamental component 42 is further removed from the amplifier 40 and applied to a frequency doubler 96, and the third harmonic output 98 from this tripler is also taken to the summing circuit 44'. and is combined there with the fundamental component 42 and the second harmonic, all of which provide an output 100 from the summing circuit 44' to the amplitude modulator 28, which It is even more free from waveband components, which would otherwise cause distortion in the stereo difference signal output (as at 50 from quadrature demodulator 36 in FIG. 1). It will be apparent to those skilled in the art to further sequentially input harmonic components to the summing circuit (44 or 44') to further reduce the stereo difference signal demodulation output distortion.

In general, as can be seen from the foregoing discussion of various types of receiver circuits according to the present invention, this type of
The inventive concept contained in the AM stereo receiver is to inversely modulate the entire wave (some with carrier enhancement, etc.) using components derived from the envelope of the received carrier, so that the stereo difference signal is quadrature demodulated. Stereo signal distortion is reduced by canceling or attempting to cancel undesirable spectral components that produce distortion when detected by a device or the like.

FIG. 4 is a diagram showing the spectrum of the modulated carrier wave received by the receiver shown in FIG. 1 and amplified by the carrier track filter circuit;
In this representative example of a received signal, the carrier is fully modulated in one stereo channel (L) and unmodulated in the other stereo channel (R).

Theoretical analysis shows that demodulation of this signal by a quadrature demodulator without any additional amplitude modulation (i.e., increased carrier output 26 in FIG.
If the received signal with a voltage ratio of about 13
% (more precisely 13.05%) and a second harmonic distortion level of approximately 2 1/2% (more precisely 2.33%)
A stereo difference output signal is produced at output 50 characterized by a third harmonic distortion level of %).
Although these amounts of harmonic distortion may be acceptable in some types of equipment, it will be appreciated that such distortion levels are excessive in terms of normal standards for commercial broadcast purposes. However, it is an important feature of this invention that such harmonic distortion levels can be readily reduced to commercially acceptable values by selective inverse modulation of the phase modulated carrier with the detected envelope wave. This is also an advantage. If it is desired to apply such inverse amplitude modulation to almost eliminate second-order distortion, theoretical considerations suggest that the inverse modulation input will reduce the rate of modulation of the phase modulated carrier by a factor of approximately 26%. It turns out. By means of inversely modulating the phase modulated carrier with the fundamental of the envelope (i.e., by opening switch 52 in FIG. ), the second harmonic distortion level is reduced to about 0.30% and the third harmonic distortion level is about 4.1%. (In a particular example, if adding inverse modulation causes a 26.09% reduction in carrier modulation, the resulting second harmonic distortion is 0.30% in voltage ratio and the third harmonic distortion is 4.13%.) %) Although such an amount of third harmonic distortion is acceptable, it is desirable to reduce this harmonic distortion as well; This can be done in the machine by closing switch 52 and applying the frequency-doubled envelope component (ie, the second harmonic envelope component) to the inverse modulation input 46 to the amplitude modulator 28. In a specific representative example, for a fundamental envelope input (at 42) of about 26% and a second harmonic envelope input (at 56 from frequency doubler 54) of about 8% in voltage ratio, the amplitude The inverted amplitude modulated, phase modulated, enhanced carrier as appearing at output 48 from modulator 28 has a spectral distribution essentially as shown in FIG. (The out-of-phase amplitude modulation fundamental wave component is 26.09%
In the particular example where the second harmonic inverse amplitude modulation is at a level of 8.115%, the spectral distribution level shown in FIG. 5 results. ) By using such inverse amplitude modulation of the fundamental and second harmonic, the specific example cited results in a second harmonic distortion level of 0.295% and a third harmonic distortion level of 0.145%. and the fourth harmonic distortion level was 0.725%.

As previously mentioned, another technique for inverse amplitude modulating a phase modulated and enhanced carrier with a fundamental envelope component and a second harmonic envelope component is shown in FIG. In this example, modulation of the enhanced carrier by the fundamental is performed in the first amplitude modulator 28', and another modulation by the second harmonic of its envelope is performed in the second amplitude modulator 28''. For example, using separate amplitude modulation stages for fundamental and second harmonic inverse modulation results in somewhat less distortion than using a single amplitude modulation stage as shown in Figure 1. I know it's small.

As a further improvement to reducing distortion in the stereo difference signal output 50 of FIG. 1, FIG. 3 shows a further alternative circuit including a frequency tripler 96 and a frequency doubler 54. provide harmonic envelope outputs 98 and 56, respectively, which are combined with fundamental envelope output 42 in summing circuit 44' to further reduce out-of-band distortion.

The distortion level of the higher-order sidebands can be further reduced by inputting the corresponding higher-order envelope components, but the fundamental and harmonic components of the received wave envelope cause the phase-modulated carrier to be phase-modulated at various relative levels. It will also be readily apparent to those skilled in the art to which this invention pertains that the technique of reducing distortion by inversely modulating the will be understood.

FIG. 6 illustrates in some detail a typical carrier track filter circuit of the type indicated generally at 20 in FIG. For a typical receiver, good carrier tracking practices to achieve an enhanced carrier signal with no substantial phase distortion, assuming that the receiver should drift within ±800 Hz according to the carrier frequency error. requires that the carrier track circuit have a bandwidth considerably smaller than ±800 Hz, which means that in addition to the desired carrier, many sideband signal components pass through a passband of this size, especially for stereo systems. This sideband component in the case of is not necessarily symmetrical, because if the passband width of the circuit is too wide, the carrier track circuit will track the phase modulation component of the stereo wave instead of passing only the carrier wave. . For this reason, the carrier track circuit shown in FIG.
In addition to the locked loop circuit (PLLA) 100, this circuit 100 uses Signetics.
A type known per se, such as that available from IC No. 562B manufactured by the company, is suitable and has a passband of ±800Hz. Phase Locked Loop 1
The output from 00 is then applied to a frequency divider circuit 104 where the frequency of the carrier wave is divided by a suitable integer such as 16. This frequency division also helps to divide the frequency error by a similar amount (but an interesting problem is that the sideband spacing is not changed by frequency division or frequency multiplication, so it is useful to make the sidebands closer together). (I don't.)
If the carrier and any frequency errors are divided by a selected integer, the reduced frequency output 106 is passed to a second phase locked loop circuit (PLLB) 108 (also using the signatures).
IC No.562B is applicable), but this circuit 1
08 has a passband of ±50Hz in the selected example. Although this circuit 108 effectively acts as a carrier tracking filter, it is sufficiently narrowband to pass little sideband modulation, so that the filtered output 110 consists essentially only of the passing carrier of reduced frequency. Become. The filtered output 110 is then filtered to isolate the original carrier frequency.
is applied to a frequency multiplier circuit 112, where it is multiplied by a suitable integer (16 in the chosen example) to produce an output 22, which is the pass carrier at the received carrier frequency. , summing circuit 24 and phase shifting network 30 (first
Figure).

Generally speaking, the carrier tracking circuit 20 should have the bandwidth to be able to track expected frequency drifts in the transmitter and receiver; May be incompatible with the use of modulation. For this reason, it may be desirable to amplitude modulate such tones on a carrier wave, thereby avoiding problems associated with circuit 20 for tracking sub-audible tones.

Because of the frequency division that occurs in stage 104 as described above and as previously described, it is necessary to compare the phase of the filter output 22 with the phase of the received carrier. This is done by feeding a portion of the output 22 in FIG. This is done by providing a control voltage input 118 to the phase locked loop circuit 100 through the phase locked loop circuit 100. The phase of the passed carrier output 22 is compared to the phase of the input wave in a phase detector 114, and a control voltage output 118 from the phase detector corrects for such large phase errors between input and output (16 frequency divisions). by 16
There are different phase stability points, and if phase detector 1
Phase Locked Loop 100 by 14
It should be noted that the phase lock loop circuit 108 can be locked at the phase stability point unless phase control is applied to the phase control. ) The control exerted on the phase lock loop 100 by the phase detector 114 is made to operate relatively slowly by the action of the low pass filter circuit 116, and is made to operate relatively slowly when the device is turned on or when the frequency division It primarily serves to correct large phase errors, such as may occur if there is severe carrier attenuation that causes circuit 104 to malfunction.

FIG. 7 is a block diagram showing a further alternative circuit which is somewhat simpler than the carrier track circuit shown in FIG. 6. In short, the phase locked loop 108 and frequency multiplication stage 112 of the circuit shown in FIG. 6 are replaced by the circuit shown in FIG. 7 (known per se).
can be replaced by Generally, this type of circuit has a frequency divided carrier output 106
is applied to a phase detector 120 whose output 122 drives a voltage controlled oscillator (VCO) 124 which generates a passed carrier output 22 at the desired frequency. VCO1
24 operates at 16 times the frequency of the input appearing at input 106, and its output 22 is also provided to a frequency divider 126 where its frequency is stepped down by exactly 1/16. An output 128 from frequency divider 126 is applied to phase detector 120;
The phase of the frequency-divided output 128 is now compared with the phase of the input signal at 106 and the phase detector 1
20 generates an output 122, which output 12
2 is utilized in VCO 124 to maintain the phase of output 22 in phase with the phase of the input signal. Viewed from another perspective, the circuit shown in Figure 7 acts as a normal phase locked loop, but with a frequency divider by 16 circuit in the return path.
And the VCO operates at 16 times the input frequency, providing accurate in-phase frequency multiplication.

FIG. 8 shows a portion of yet another type of AM stereo receiver according to the invention, the circuitry of which is shown in FIG. It is similar to that shown in Figure 3). Instead of the envelope detector 18 in the circuit of FIG.
A product demodulator 18' is utilized as an in-phase detection device for extracting the signal output 38, to which the pass carrier input 22 is also applied. Although the product demodulation circuit 18' is somewhat more complex than the envelope detector 18, it is advantageous from the standpoint of improved signal-to-noise characteristics and is currently desirable, especially under noisy reception conditions. ing.

From the foregoing, further modifications, adaptations and applications of the stereo receiver according to the invention and its components will occur to those skilled in the art to which the invention pertains.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a typical compatible AM stereo receiver according to the present invention. FIG. 2 is a block diagram showing a portion of another type of AM stereo receiver according to the present invention; the other portions of this receiver are similar to those shown in FIG. FIG. 3 is a block diagram showing a portion of yet another type of AM stereo receiver according to the present invention, the other parts of which are similar to those shown in FIG. FIG. 4 is a diagram illustrating the spectrum of a modulated carrier (such as at 26 in FIG. 1) received and carrier multiplied by the receiver shown in FIG. FIG. 5 shows the spectrum of the amplitude modulator output (such as at 48 in FIG. 1) corresponding to the received signal spectrum shown in FIG. FIG. 6 is a more detailed block diagram of the typical carrier track circuit used in FIG. FIG. 7 is a configuration diagram showing a modified portion of the circuit shown in FIG. 6. FIG. 8 is a block diagram showing modified parts of the receiver shown in FIG. 1. 14: superheterodyne circuit, 18: envelope detector, 20: carrier track filter circuit, 24: summing circuit, 28: amplitude modulator,
30: +90° phase shift network, 34: product demodulator, 36: quadrature demodulator, 40: amplifier, 44: summation circuit, 54: frequency doubler, 58: electronic switch, 60: -45° phase shift circuit network, 64: addition circuit,
66: Subtraction circuit, 68: +45° phase shift circuit network, 7
4: 15 cycle band filter, 78: amplifier, 8
4: Detector, 96: Frequency tripler, 100: Phase locked loop A, 104: Division circuit,
108: Phase locked loop B, 11
2: Multiplier circuit, 114': Phase detector, 120:
Phase detector, 124: Voltage controlled oscillator, 12
6: Divided circuit.

Claims (1)

[Claims] 1. A compatible amplitude modulation type stereo receiver of a type that receives a carrier wave that is amplitude modulated with stereo sum (L+R) received information and phase modulated with stereo difference (L-R) signal information. , (a) representing the envelope of the received carrier and thus representing the stereo sum (L+R) signal information;
(b) a quadrature demodulator to extract the (L-R) audible signal; and (c) a component representing the envelope so as to provide L and R stereo signal outputs. (d) means for generating a component obtained from the components representing said envelope; (e) demodulation (L-R) induced by quadrature demodulation; R) means for inverse amplitude modulating a phase modulated carrier wave with a component obtained from said means prior to quadrature demodulation of the carrier wave in order to reduce distortion in the output signal; an apparatus for demodulating the output subaudible tones, the output subaudible tones being additionally modulated with subaudible tones indicative of
and an R stereo signal output, and includes a device for controlling an audible output channel of the receiver to provide a monophonic output in the absence of such subaudible frequency tones. 2. The compatible amplitude modulation stereo receiver according to claim 1, wherein the detection device is an envelope detection device. 3. The compatible amplitude modulation stereo receiver according to claim 1, wherein the obtained component represents at least an envelope fundamental wave. 4. A compatible amplitude modulation stereo receiver according to claim 1, wherein the obtained components represent at least an envelope fundamental wave and a second harmonic. 5. A compatible amplitude modulation stereo receiver according to claim 1, wherein the obtained components represent at least an envelope fundamental wave, a second harmonic, and a third harmonic. 6. A compatible amplitude modulated stereo receiver according to claim 1, wherein the sub-audible frequency sound has a frequency of about 15 Hz. 7. A compatible amplitude modulated stereo receiver according to claim 1, wherein the received carrier wave is phase or frequency modulated with subaudible frequency sound. 8. A compatible amplitude modulated stereo receiver according to claim 1, wherein the received carrier wave is amplitude modulated with a subaudible frequency sound. 9 A compatible amplitude modulation stereo receiver that receives a carrier wave that is amplitude modulated with stereo sum (L+R) signal information and phase modulated with stereo difference (L-R) signal information, which includes: (a) Received carrier wave; , thus representing the stereo sum (L+R) signal information,
(b) a quadrature demodulator to extract the (L-R) audible signal; and (c) a component representing the envelope so as to provide L and R stereo signal outputs. (d) means for generating a component obtained from the components representing said envelope; (e) demodulation (L-R) induced by quadrature demodulation; R) a device for inverse amplitude modulating a phase modulated carrier wave with a component obtained from said means prior to quadrature demodulation of the carrier wave in order to reduce distortion in the output signal; and (f) inverse amplitude modulation with said device for inverse amplitude modulation. (g) the received carrier wave is additionally modulated with a subaudible tone indicative of the presence of a stereo signal; and apparatus for demodulating the output subaudible tone; and L in response to the presence of such sub-audible frequency sounds.
and an R stereo signal output, and includes a device for controlling an audible output channel of the receiver to provide a monophonic output in the absence of such subaudible frequency tones. 10. The compatible amplitude modulation stereo receiver according to claim 9, wherein the detection device is an envelope detection device. 11. The compatible amplitude modulation stereo receiver according to claim 9, wherein the obtained component represents at least an envelope fundamental wave. 12. A compatible amplitude modulation stereo receiver according to claim 9, wherein the obtained components represent at least an envelope fundamental wave and a second harmonic. 13. A compatible amplitude modulation stereo receiver according to claim 9, wherein the obtained components represent at least an envelope fundamental wave, a second harmonic, and a third harmonic. 14. The device for enhancing the carrier of the received carrier includes a carrier track circuit that separates the carrier frequency from the received carrier, and a device that combines a portion of the received carrier with the output of the carrier track circuit. A compatible amplitude modulation stereo receiver according to claim 9. 15 The carrier wave track circuit includes a first phase lock loop circuit, a frequency division circuit, a second phase lock loop circuit having a pass band smaller than a pass band of the first phase lock loop circuit, and the first phase lock loop circuit. a frequency multiplier circuit for restoring the frequency of the output of the second phase lock loop circuit to have the same wave number as the input carrier wave to the circuit; It is characterized by comprising a circuit for comparing the carrier wave output of the lock loop circuit and controlling the phase of the output from the first phase lock loop circuit in order to maintain the input and the output of the carrier wave track circuit to be in phase. A compatible amplitude modulation stereo receiver according to claim 9. 16. The compatible amplitude modulated stereo receiver of claim 9, wherein said sub-audible frequency sound has a frequency of about 15 Hz. 17. A compatible amplitude modulated stereo receiver according to claim 9, wherein the received carrier wave is phase or frequency modulated with subaudible frequency sound. 18. A compatible amplitude modulated stereo receiver according to claim 9, wherein the received carrier wave is amplitude modulated with subaudible frequency sound.