Abstract: A stereo demodulation device includes an audio signal processing circuit, a muting circuit, a muting switch, and a variable resistor. At least a given signal processing function of the audio signal processing circuit is adjusted by supplying a control current from a control terminal thereof. The muting circuit outputs or blocks an audio signal processed by the audio signal processing circuit. A muting switch is commonly connected to a control terminal of the muting circuit and the control terminal for the given signal processing function of the audio signal processing circuit. The variable resistor adjusts the control current.

Abstract: To counter the effects of multipath on the signal received at the receiver of an FM stereophonic broadcasting system utilizing companding of the stereo difference signal, the normal operation of the expander embodied in the receiver is automatically modified in response to detection of multipath so as to minimize such effects and thereby improve the quality of the reproduced signal. In the preferred embodiment, a substantially fixed or steady control voltage replaces the normal dynamically varying control signal for the variable gain element of the expander during occurrences of multipath disturbances in excess of a predetermined severity. Another aspect of this embodiment is that a D.C. correction voltage having an amplitude proportional to the severity of the detected disturbances is combined with the fixed control voltage for the variable gain element in a manner to reduce the gain of the element thereby to further reduce the effect of the disturbance.

Abstract: A circuit for separating FM signals from a composite signal utilizes a comb filter having successive frequency response nulls which span the frequency spectrum of the FM signal to be separated. The comb filter response is phase linear and defines the pass-band of the desired signal. A nonideal or phase nonlinear bandpass filter can be cascaded with the comb filter to attenuate out of band signals. The cascade combination of the comb filter and nonlinear bandpass filters is a cost effective substitute for the conventional, complicated phase linear bandpass filter having a boxcar frequency response traditionally used to separate FM signals.

Abstract: In a sound multiplex television tuner, when the input field strength becomes smaller than a certain value, a level control means continuously attenuates the sub signal demodulation output with the aid of the field strength detection signal which a field strength detector circuit provides according to the input field strength. The characteristic of response to input field strength of the level control means is switched, according to a given sound multiplex mode, so that its operation becomes most suitable for the sound multiplex mode, thereby to suppress the noise without causing the television viewer to feel a sense of incongruity in the perceived sound.

Abstract: Pilot signal cancelling circuitry for removing the pilot signal from a composite signal, includes a subtraction circuit. The composite signal and a synthesized pilot signal are coupled to the minuend and subtrahend input connections of the subtraction circuit respectively. The output of the subtraction circuit is coupled to first and second multipliers. A cosine signal of like frequency to the pilot signal is applied to the first multiplier which develops a phase error signal. The phase error signal is coupled to an oscillator which develops the cosine signal. A sinusoidal signal, also developed by the oscillator and in phase with the pilot signal is applied to a second multiplier. The second multiplier generates a signal proportional to the amplitude of the residual pilot signal in the output signal provided by the subtraction circuit. The amplitude signal is multiplied by a sinusoid in phase with the pilot signal in a third multiplier to generate the synthesized pilot signal.

Abstract: A radio receiver most suitable for use in a car includes a pulse count demodulating circuit and a second demodulating circuit other than a pulse count detecting circuit so that a demodulation signal from selected one of the demodulating circuits is supplied according to the level of a detection signal supplied from a received electric field intensity detecting circuit.

Abstract: A demodulating system for the multivoice TV system, which is constituted so that a tuner is tuned to receive the sum signal and the difference signal of an aural signal and a pilot signal which are transmitted together with a video signal, the selected signal is given to an intercarrier demodulator and an aural signal band-pass filter, the intercarrier demodulator provides a beat signal corresponding to the difference between the video carrier and the sound subcarrier, the beat signal is demodulated to obtain the sum signal, and the sound subcarrier provided by the sound signal band-pass filter is demodulated to obtain the difference signal and the pilot signal. The demodulating system is intended to eliminate disturbing signals included in the composite signal and buzzing, and to obviate the malfunction of the MPX decoder due to the disturbing signal having the same frequency as that of the pilot signal.

Abstract: A control circuit in an FM radio receiver includes a current mirror circuit which extracts a ripple component caused by a multipath disturbance and superposed on an S-meter output voltage from an intermediate frequency amplifier/detector of the FM radio receiver, and decreases the S-meter output voltage in response to the degree of the ripple component to use the decreased S-meter output voltage as a control voltage for control of separation and high-cut operations of a stereo demodulating stage of the FM radio receiver.

Abstract: A companding system for a television audio apparatus includes a compressor and an expander for stereo difference signals. The compressor provides variable preemphasis of high frequency signal components and the expander provides complementary variable deemphasis. At the receiver, unwanted signals are generated by a mixer that demodulates the stereo difference signal. The unwanted signals can cause mistracking of the expander relative to that of the compressor. A filter to eliminate the effect of these unwanted signals is placed in the expander control circuit, rather than the difference signal path. This eliminates the need and expense of an equalizing filter in the sum signal path.

Abstract: An FM transmission system and method in which a gain control signal is generated and used to encode the audio signal in accordance with a predetermined compression curve. At the receiver the gain control signal is recovered and used to decode the audio signal, thereby providing a faithful reproduction of the original signal regardless of which compression curve is used. The compression curve can be tailored for optimum results for receivers with and without the decoding circuitry, depending upon the program material. The audio signal is delayed in the encoder while the gain control signal is generated, allowing the control signal to fully respond to changes in the audio signal without clipping the audio signal. The gain control signal is segregated from interfering with the remainder of the transmitted signal by restricting it to a low frequency bandwidth centered on the 38 KHz subcarrier for the L-R signal, and placing it in phase quadrature relation to the remainder of the transmitted signal.

Abstract: A high-cut and high-blend control voltage generating circuit for activating a noise reduction circuit of an FM stereo receiver is configured to be simply responsive to multipath noises and never to plug noises. A changing and discharging circuit in the control voltage circuit may have a relatively long charging time constant, and the voltage control circuit may be configured to be simply responsive to multipath noises above a predetermined level. Thus the circuit is much less liable to operate erroneously.

Abstract: A stereophonic receiving circuit in which automatic switchover from the monaural receiving mode to the stereophonic receiving mode as the input signal strength increases is made more smoothly and effectively by boosting the gradient of a S-meter control voltage above a certain level of the received signal. The conventional S-meter voltage is applied to one input of a differential amplifier, the other input of which receives a reference voltage. The output of the differential amplifier is applied to one input of an analog OR gate, the other input of which receives the S-meter voltage directly. The output of the analog OR circuit, which is the greater of the two inputs to the circuit, is applied to the control inputs of an electronic volume control circuit, a high-cut controller, and a stereophonic demultiplexer circuit.

Abstract: A noise eliminating circuit including a subsignal modulator circuit, a matrix circuit, and sample-and-hold circuits, for reducing signal distortion as well as preventing the in-circuit generation of noise. The sample-and-hold circuits are disposed in the signal paths of a main signal and the demodulated subsignal and are operated by a signal synchronous with a noise component. The holding times of the two sample-and-hold circuits may be made different from one another.

Abstract: In a demodulator comprising an indicator (31) for indicating either stereo reception or monaural reception, an indicator circuit (30) is used to cancel a pilot signal included in a stereophonic signal and to produce a drive signal for driving the indicator. The indicator circuit comprises a negative feedback loop formed by an adder circuit (41), a phase detector (43), and a cancellation circuit (45). The cancellation circuit supplies the indicator and the adder circuit with the drive signal and a cancelling signal synchronized with and approximate to the pilot signal, respectively. The adder circuit substracts the cancelling signal from the pilot signal to deliver an intermediate signal to a multiplex decoder and to the cancellation circuit through the phase detector. The cancellation circuit comprises a wave generator for generating a pair of currents proportional to an amplitude of the pilot signal and a level adjusting circuit for converting one of the currents into the cancelling signal.

Abstract: A circuit is provided for detecting the level of noises in received FM signals in an AM/FM receiver which includes at least an FM intermediate-frequency amplifier, an FM detector connected thereto, an AM intermediate-frequency amplifier and an AM detector connected thereto. This FM noise level detecting circuit includes a frequency converter receiving the output of the FM detector for converting noise components contained in the output of the FM detector into a noise signal of the AM intermediate-frequency, which is in turn outputted to the AM intermediate-frequency amplifier, so that the converted noise signal is amplified by the AM intermediate-frequency amplifier and then detected by the AM detector to produce a DC signal. The signal thus obtained is not only representative of the level of the noise contained in the received FM signal, but also representative of the received FM signal strength.

Abstract: Improved FMX Companding apparatus for FM transmitter. A pilot subsystem which is substantially identical to the FMX audio path is used to develop a control signal which provides amplitude control through a VCA in the main FMX audio path.

Abstract: An FM stereo receiver has a loop having a negative loop gain for the pilot signal contained in the input signal in the form of a frequency modulation. As a result thereof the frequency modulation of the input signal is reduced or suppressed by the pilot signal, so that the interference introduced by this pilot signal is also reduced or suppressed.

Abstract: In an FM-stereo receiver the demodulated stereo-difference signal is mixed with a non-sinusoidal signal of the sub-carrier frequency and the mixing product is used to modulate the frequency of an oscillator by means of which the aerial signal is converted to the intermediate frequency range. Interference in the reception is avoided because of the fact that the signal used for modulating the oscillator is free from third and fifth harmonics of the sub-carrier frequency.

Abstract: Certain, but not all AM stereo radio broadcasting and reception systems suffer from a severe form of reception anomaly wherein the perceived stereo image moves from side to side, back and forth, which effect has come to be known as "Stereo Platform Motion" or simply "Platform Motion". A prior art patent proposed a method for sensing reception conditions conductive to Platform Motion and then switching the receiver from stereo to monophonic reception to avoid Platform Motion. The present invention enables the AM stereo receiver to maintain stereo operation under such reception conditions, and instead of switching the receiver to monophonic operation, it switches the receiver to a different method of stereo reception that does not suffer from Platform Motion.

Abstract: A low-pass filter circuit for suppressing a subcarrier contained in an FM stereo demodulation signal in which the output signal of the circuit is unaffected by magnetic distortion. The FM stereo demodulation signal is applied through a low-pass filter to n sample-and-hold circuits connected in parallel with one another. The outputs of the sample-and-hold circuits are summed to form an output signal in which the subcarrier signal has been suppressed. The n sample-and-hold circuits are driven with a corresponding number of sampling pulse signals of different phases.

Abstract: An automatic frequency control circuit is used in an FM stereo radio receiver which includes an intermediate frequency amplifying and detecting circuit producing an output for driving a signal meter and includes a multiplexer, so that the multiplexer effects controls to reduce noises in stereophonic and monophonic reception responsively to the signal meter driving circuit by changing its separation ratio and attenuation ratio.

Abstract: A control circuit is configured to detect by an active filter white noise levels in detection outputs from an intermediate frequency amplifier in an FM stereo demodulation circuit so as to control the separation of outputs from the stereo demodulation circuit into left and right stereo channels, responsively to the white noise level, and is characterized in provision of a current detection circuit which is actuated by the output from the active filter and responsive to a current flowing into a resistor connected between the feedback terminal of the active filter and a reference potential point to control a blend control circuit so as to change the point whereat the separation ratio begins to vary.

Abstract: A signal mixing circuit for blending two signals, such as left and right channel FM stereo signals, blends the two signals at each of two outputs in response to a variable control voltage, which acts upon a transistor network connected between the two signal paths. When the variable control voltage is determined by an amplitude detector connected in a conventional FM stereo receiver, the output signals will be blended to a greater degree when the received signal strength of the broadcast FM signal becomes weaker. In a further embodiment, capacitors are added to inhibit high-frequency components of one channel and to add in high-frequency components of another channel thereby eliminating and cancelling the noise components normally present in the respective signals and improving the S/N ratio.

Abstract: An FM receiver for demodulating an RF carrier signal containing a pilot frequency signal is provided. The receiver includes first and second frequency control loops. The first frequency control loop selects the local oscillator signal frequency. The reference signal oscillator in the first frequency control loop forms a part of a second frequency control loop. The second frequency control loop locks the phase of the reference signal oscillator with a detected pilot signal. In this way, the tuning signal of the local oscillator is kept phase locked to the detected pilot signal. Additional provisions are provided for changing the divisor of the second phase lock loop such that the time for establishing phase lock is reduced.

Abstract: A stereophonic broadcasting system incorporating companding of the difference signal in which both the usual difference signal and a compressed version of the difference signal are transmitted to one or more remote receivers. At the receiver the usual, unchanged, difference signal is used as a reference signal for controlling the expansion of the compressed difference signal so as to cause the amplitude of the companded difference to equal the level of the usual difference signal. Thus, the expander is adaptive to any compression characteristic that might be employed at the transmitter. Further, the availability of the usual uncompressed difference signal at the receiver enables the adaptive decoding of dynamic parameters of the received signal, such as frequency response and attack and recovery times, so that all of the parameters of the original signal can be restored automatically.

Abstract: A stereophonic broadcasting system incorporating companding of the difference signal in which both the usual difference signal and a compressed version of the difference signal are transmitted to one or more remote receivers. At the receiver the usual difference signal and the compressed difference signal are combined and the resulting signal then expanded to obtain a noise-reduced difference signal for matrixing with the sum signal to obtain the original left and right signals. Utilizing both difference signals increases the effective level of the received difference signal by 6 dB, whereas the noise is increased only 3 dB, for a net improvement of 3 dB in signal-to-noise ratio. Utilization of both difference signals at the receiver also permits compression of the difference signal according to any desired compression law.

Abstract: In a television system for recovering a stereophonic sound signal including a subcarrier signal, apparatus is provided including a bandpass filter for sensing the noise density of the recovered sound signal. A detector generates a control signal corresponding to the noise density sensed by the filter. The control signal is used to progressively attenuate the level of the subcarrier signal in response to increases of the sensed noise density. Although this gradually reduces the stereophonic separation, it provides a corresponding increase in the signal-to-noise ratio of the resulting reproduced stereophonic signal.

Abstract: There is disclosed a distortion cancel circuit in FM stereo receiver, which circuit synthesizes a canceling signal mainly including the distortion component by performing the arithmetic operation for an FM demodulation signal and adjusts the level of this synthesized canceling signal and thereafter subtractively combining it with the FM demodulation signal. This circuit enables the elimination of harmonic distortion which appears in the stereo MPX signal output due to the band characteristic of an intermediate frequency amplifier.

Abstract: In a noise reduction circuit for reception of stereophonic FM signals in which the demodulated signal is chopped at twice the pilot frequency for separation between left- and right-channel signals, the demodulated signal is sampled by a first sample-and-hold circuit in response to the output of the noise detector to store that portion of the signal which appeared immediately prior to the occurrence of an impulse noise. The demodulated signal is also sampled by a second sample-and-hold circuit at a frequency twice the pilot frequency to eliminate a noise which might arise due to the chopping of the demodulated signal. A signal is derived from the outputs of the first and second sample-and-hold circuits that indicates the slope ratio of the demodulated signal at the moment that occurred immediately prior to the impulse noise.

Abstract: A stereophonic receiver includes internal separation control in which the sound separation is directly in accordance with noise reduction need and the amplitude and frequency of the sound signals monitored. Each sound channel is similar and includes an input buffer and an output buffer to directly transmit the corresponding channel signal. A variable highpass filter unit interconnects the output buffer of each channel to the opposite channel, and includes a voltage sensitive input to control the transmitted signal level. A control channel includes a high frequency filter to pass the high frequency signal of the stereophonic sound, which signal is rectified and filtered by suitable attack and decay filters. A log-conversion unit senses and converts the filtered signal to a C. logarithmic D.C. signal, which is directly proportional to the amplitude and frequency of the corresponding channel stereophonic signal. The D.C.

Abstract: A clock-controlled filtering arrangement for suppressing a number of interference frequencies related to a clock frequency, which comprises a time-discrete comb filter included in a negative feedback loop for a selective negative feedback of the said interference frequencies, which time-discrete comb filter is connected to an output of a clock generator for controlling the frequency location of the pass ranges of the comb filter. In order to avoid on the one hand the introduction of quantizing noise and the use of additional circuits, such as A/D and D/A converters, and on the other hand the occurrence of error cumulation while maintaining an adequate interference suppression, the time-discrete comb filter is of the switched capacitor N-path filter type.

Abstract: In a distortion canceller to remove the distortion of a demodulated signal in an FM receiver, the n-th power of the demodulated FM signal is produced and then differentiated to derive an n-th order distortion signal. The derived n-th order distortion signal is adjusted in its amplitude level and then combined with the demodulated FM signal so that the n-th distortion component can be cancelled.

Abstract: A stereo multiplex circuit which can reduce a distortion of an FM demodulated signal to be generated due to nonlinearity of the frequency vs. amplitude/phase characteristics of a band-pass filter at an intermediate frequency amplifier stage of an FM receiver. This circuit includes a circuit for multiplying signals consisting of right-channel and left-channel signals and for adjusting the level of this multiplication signal into a suitable magnitude and thereafter inserting into the right and left channels, thereby causing a harmonic distortion to disappear.

Abstract: A signaling system for FM transmission systems is disclosed that utilizes one or more so-called quadrature subcarriers for transmitting at least one data signal, including signaling tones, digital data, program material, or the like. The signal is modulated on outer edges of the quadrature channel so as to minimize crosstalk interference with the conventional FM stereo difference channel subcarrier and to place the signals in regions of low hearing acuity. Use of a quadrature subchannel also enables a signal to be modulated onto the quadrature subcarrier to provide the capability of modulating a noise compressed difference signal in a manner so as to minimize degrading crosstalk with the adjacent difference channel subcarrier. A receiving apparatus is disclosed for decoding the quadrature subcarrier data independently of standard FM stereo demodulation.

Abstract: A stereo pilot signal detector for an AM stereo receiver connects an input signal to a train of pulses corresponding to zero crossings of the input signal. These pulse lock a shift register having a data input connected with a timer which is reset from the pulses after the shift register is clocked. The timer produces a logic "1" input to the register during a time interval extending on either side of the zero crossings of the stereo pilot signal. If four consecutive zero crossings occur within the window, the stereo decoder and an indicator are enabled. Thereafter, if three out of four zero crossings occur outside said interval, the stereo decoder and indicator are disabled.

Abstract: Disclosed is an FM stereo demodulator in which components of the demodulated signal corresponding to odd harmonics of the subcarrier signal are eliminated.In order to prevent the production of odd harmonics, the multiplication between positive and negative sinusoidal subcarrier signals is performed with a stereo pilot signal and positive and negative pulse train signals produced by pulse detection of an FM signal.The multiplication signals are further added with each other to directly reproduce left and right stereophonic signals.

Abstract: An FM stereo demodulator having improved separation and distortion characteristics comprising a high-frequency pulse signal which is modulated by a sinusoidal subcarrier signal produced in accordance with a stereo pilot signal. The high-frequency pulse signal is multiplied with a composite signal at a multiplier so as to reproduce left and right signals without frequency components of noise. Constructed accordingly, the invention advantageously obviates the use of a low-pass filter which injects delay characteristics and reduces gain of the composite signal from an FM demodulator.

Abstract: FM-receiver comprising an aerial input having connected thereto, in succession, an RF input stage, an IF portion, an FM-detector and a stereo decoder having a mono-stereo control circuit therein, also a control signal generating circuit being connected thereto, the control signal generating circuit comprising a multipath reception detector and being connected to the IF portion via a level detector, the multipath reception detector comprising an amplitude detector connected to the level detector via a bandpass filter. The FM-receiver also comprises a noise pulse suppression circuit arranged between the FM-detector and the stereo decoder for keeping the amplitude of the stereo multiplex signal constant during the occurrence of noise pulses.

Abstract: A noise removing apparatus in an FM receiver includes a high-pass filter (29) receiving an output from an FM detector circuit (11), a gate (15) being interrupted in response to a pulsive noise detected by level-discriminating an output from a variable gain amplifier (35) receiving an output from the high-pass filter (29). Transistors are provided for controlling the gain of the variable gain amplifier (35) according to the magnitude of a terminal voltage of a capacitor which is charged according to an output from a rectifying circuit (43). The noise removing apparatus further includes a voltage generator (51) for generating a voltage proportional to a received electric field strength and a circuit (53) for varying an amount to be charged in the capacitor according to the magnitude of a voltage from the voltage generator (51) for maintaining the gain of the variable gain amplifier (35) large at the time of strong electric field, so that a multipath noise can be effectively removed.

Abstract: An output matrix adapted to receive an L+R signal component (made up of the sum of L and R stereo components) and an L-R signal component, and to combine these in a manner to produce a separate L output and a separate R output, with certain modifications to the outputs. The higher frequency portion of the L-R signal is passed through a detector which, in turn, causes a leading edge amplifier to transmit to the matrix only those signal portions where there is a relatively abrupt change of amplitude, these being the signal portions which contain the main stereo information which gives the directional information. Also, the L+R signal component, in addition to being transmitted directly to the matrix, is directed through time delay means to produce a time delayed L+R signal component that is also transmitted to the matrix, so as to provide what are called "ambient" to the output of the matrix.

Abstract: An FM stereophonic receiver is arranged so that a central processing unit assigned for selection of a broadcasting station is burdened, based on a clock pulse of the central processing unit, to generate sub-carriers synchronized with a pilot signal contained in a composite signal, for being used in multiplex demodulation, whereby to improve signal-to-noise ratio of the multiplex demodulated signals, and to simplify the circuit arrangement of the receiver.

Abstract: An FM noise reducing circuit which comprises an operational amplifier for comparing intermediate frequency signal levels and multipath signal levels, and a multiplexer controlled by output signals from the operational amplifier is arranged to carry out attenuation of high frequency components as well as blending of outputs from right and left channels in response to the output signals of the operational amplifier.

Abstract: A pulsive noise removing apparatus comprises a subtracting circuit (35) receiving one input thereto a stereo composite signal directly from a delay circuit (31). A stereo switching signal is generated as a function of a stereo pilot signal included in the stereo composite signal and a cancel signal of the same level, the same frequency and the same phase as those of the stereo pilot signal is generated as a function of the stereo switching signal. A gate (67) is interposed between the output of the cancel signal generating circuit (65) and the other input of the subtracting circuit and the gate is interrupted responsive to detection of a pulsive noise included in the composite signal. The pulsive noise is removed due to interruption of the gate and the stereo pilot signal is prevented from appearing at the output of the subtracting circuit irrespective of conduction or interruption of the gate.

Abstract: Receiver comprising a field-strength detector for measuring the received signal amplitude and a noise reduction circuit connected thereto via a control signal generating device for reducing audio-frequency noise in the output signal of the receiver, which control signal generating device has an attack and a recovery time constant at a decrease and an increase, respectively, of the received signal amplitude measured by the field strength detector, the recovery time constant being greater than the attack time constant. By adequate control of the cross-talk attenuation of a stereo signal and of the audio band-width, sudden variations in the sound quality at rapid and large field strength variations are prevented. To this end the control must be continuous and must, in the event of field strength variations follow the decrease of the field strength more rapidly than the increase.