Abstract: Disclosed is a pilot signal cancelling system employed in an FM stereo receiver which does not cause deterioration of the S-N ratio.

Abstract: There is provided a FMX ID signal detection apparatus for discriminating between a FM broadcasting by means of a FM signal including a sum and difference signals M and S obtained from stereophonically related audio frequency source signals by matrix processing and a FMX broadcasting by means of a FMX composite signal including a compressed difference signal SD obtained by compresssing the dynamic range of the signal S, a FMX identification signal and the signals M and S.

Abstract: Volume control for use in a cable television set top converter or the like is calibrated for optimum television stereo channel separation. The volume control controls the volume to predetermined levels. One of the predetermined levels is a particular level calibrated for optimum stereo separation. An indicator on the converter indicates the optimum stereo separation volume level. When an internal VCR timer turns on the set top converter, the set top converter is forced to the optimum stereo separation volume level. The calibration is performed during manufacture and ensures that the indicated volume level for optimum stereo separation is indeed the optimum volume level.

Abstract: In this radio receiver, the charge on a capacitor (14) controls the bandwidth of filters in the receiver's audio circuits. When tuning the radio, a bandwidth control circuit (13) forces this capacitor (14) to discharge, thereby forcing the audio path to be bandwidth restricted, thereby minimizing interstation noise reproduction.

Abstract: A stereo FM radio transmission system with FMX transmission and reception capability includes a transmitter that transmits a pilot-coherent FMX-tone indicator signal at a frequency of an exact integer submultiple of the pilot frequency. The system also includes a receiver for dividing the frequency of the received pilot signal by various submultiples, nearly equal to the exact submultiple, toward quickly finding a match in phase of the received tone and the received pilot and finally dividing the pilot by the exact submultiple to establish an operational lock mode of the receiver tone detector to keep-on an FMX-indicator lamp, to change the receiver decoder to an FMX-reception operating mode and to stand by to quickly recapture the pilot and FMX-tone in the event of multipath or other interfering signals.

Abstract: Disclosed is a circuit for controlling the activation of a stereo indicator and a tune indicator in an AM stereo receiver. In the preferred embodiment, a pilot tone detector is employed to determine if the input signal is a stereo signal and an AGC is used to detect a preselected improvement in the amplitude of the received signal. A capacitor is charged in response to the stereo or the amplitude condition. When the charge level of the capacitor reaches a first predetermined level, a tune indicator driver is enable to allow a tune detect circuit to drive the indicator. This prevents the tune indication from activating before the receiver is stabilized. When the charge level of the capacitor reaches a second predetermined level, a stereo indicator driver gradually activates the stereo indicator. This prevents sudden power drains from adversely affecting the circuit.

Abstract: The relative phase polarity between two acoustic or electric signals is determined easily, quickly and conclusively with a hand-held instrument providing immediate visual polarity indication. Built-in dual-channel amplification enables a pair of microphones to be utilized as acoustic probes, of particular versatility and benefit in the audio sound field, enabling extremely efficient and virtually fool-proof verification of relative phase polarity between two loudspeakers in practically any sound system or environment during normal operation from almost any source, monophonic, stereophonic, music, speech or even noise, without any dismantling, trial-and-error experimentation, subjective guesswork or other uncertainties usually associated with speaker phasing. An OR-function detector selects the stronger of the two signals under test for comparison with a sum signal derived in an instantaneous summing circuit.

Abstract: A simplified stereo signal decoder is disclosed for use in an AM stereo receiver which receives composite AM stereo broadcast signals comprising a radio frequency carrier wave having amplitude modulation representing stereo sum (L+R information and phase modulation representing stereo difference (L-R) information. The decoder makes novel use of a common, commercially available integrated circuit (IC) that normally is used as a tone detector or a frequency-modulation (FM) detector. The decoder provides synchronous detection of the (L-R) information, combined two-mode phase-locked loop (PLL) recovery of the carrier component and enabling of the (L-R) signal output, and delayed enabling of the (L-R) signal output for a "stereo bloom" effect. The decoder is particularly useful for decoding independent sideband (ISB) AM stereo broadcast signals.

Abstract: In a radio having an in phase multiplier (A) for providing an in phase detected signal, a detection unit for receiving this signal and for determining whether this signal includes any negative polarity components which would indicate that a viable broadcast signal does not exist on the incoming frequency of interest. This detection unit can include a comparator (11) for comparing the incoming signal against a selected reference value. The invention can also include a signal quality evaluation unit (58) for providing either a digital or analog quality signal that can also effect the output and be used by appropriate processing circuitry to further refine the channel selection process.

Abstract: An apparatus is disclosed which provides a display of the stereo image and aural perspective of stereophonic sounds. Left and right signal are processed to form rectified sum and difference signals which are applied to the signals which are applied to the vertical and horizontal deflection electrodes of an oscilloscope.

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 receiver having a tuner for tuning to a desired broadcast station and connected with a detector through which a demodulated signal is supplied as an input signal to a function selector which receives at least one other input signal from another source thereof and which selects either the demodulated signal or the other input signal as the output signal therefrom, a tuning control for selecting the broadcast frequency to which the tuner is adjusted and a volume control for adjusting the volume of the output signal from the function selector; is provided with a common display device, desirably constituted by a row of bar-type display elements, which selectively displays either the broadcast frequency, when the function selector selects the demodulated input signal, or the volume level when the function selector selects the other input signal or when the volume control effects a change in the volume level.

Abstract: A sound-multiplexed TV signal demodulator includes a stereo demodulation means having a first phase-locked loop of a first voltage controlled oscillator and also having a first frequency divider and a first comparator, an L-R demodulator and a matrix circuit, a SAP demodulation means having a second voltage controlled oscillator and a second comparator, a SAP detector detecting absence of the SAP signal to produce a detection signal when the SAP signal is not received, means by using a signal obtained from the first frequency divider for producing a reference signal having a frequency integer times as high as the frequency of the stereo pilot signal, and means for fixing the oscillation frequency of the second voltage controlled oscillator at the reference frequency in response to the detection signal.

Abstract: In a stereophonic broadcasting receiver, a single indicator with two levels of illumination serves to provide indication of both accurate tuning and the presence of stereophonic signals. One signal or a combination of signals related to the tuning circuits of the receiver cause the indicator to be illuminated to a perceptible level. When, by use of a pilot tone detector, it is certain that stereophonic signals are being received, additional current is caused to flow through the indicator, raising the illumination to the maximum allowable level. The circuit has particular application to manually tuned receivers.

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: An equalizer apparatus for audio equipment capable of selecting between a 2-speaker system and a 4-speaker system, including a display device indicating proper operation of the control knobs of the equalizer. The display device includes a first illuminable element of a first color for indicating operation of one channel of stereophonic sound reproduction, a second illuminable element of a second color for indicating operation of the other channel of stereophonically reproduced sound, and color coded means corresponding to said first and second colors for indicating which of the control knobs produce data signals for the first channel and which of the control knobs produce data signals for the second channel. Further, the color coded means may indicate which of the control knobs produce data signals for each of the divided frequencies of the respective channels during operation of the audio equipment in the manner simulating quadriphonic sound.

Abstract: In a circuit for indicating reception of stereo signals (for use in e.g. a radio tuner or television) audio signals prevailing in the left (L) and right (R) output channels are applied to respective limiting circuit and the output signals derived are fed to OR gate. When a monoaural signal is detected, the signals in the two output channels will be in coincidence and so the output from the exclusive OR gate remains low. When stereo signals are detected, however, a finite phase difference exists between the two signals and the output for the OR gate is correspondingly high. A Schmitt trigger drives an LED display whenever the output from the OR gate exceeds a preset threshold level to provide an indication that a stereo signal is being reproduced. A capacitor/resistor circuit imposes a time delay on level changes at gate so that the LED display remains illuminated, even during momentary interruptions of the audio signal.

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.