Abstract: Multi-system or "universal" AM stereo receivers are provided which require no switching of the receiver's stereo decoder circuitry regardless of which AM stereo system signal is being received. In accordance with one aspect of the invention, acceptable stereo sound is achieved for all AM stereo systems by introducing a selected amount of distortion correction in the L-R channel of the universal receiver and a selected phase difference between the L+R and L-R channels. In addition, perceived stereo separation in AM stereo and other stereo receivers is enhanced by also properly selecting the gain in the L-R channel in relation to the L+R channel.

Abstract: An FM stereo generator for use as a modulator or in a test instrument or the like to provide the conventional 19 KHz and 38 KHz signals. The phase of the generated 19 KHz pilot subcarrier signal is fixed relative to the 38 KHz carrier signal. The 38 KHz double sideband suppressed carrier signal is generated in a digital synthesis circuit to provide a stable 38 KHz carrier signal. The left and right stereophonic audio signals are applied to operational amplifiers to provide sum and difference audio components. The difference component is applied as an input to a double sideband suppressed carrier digital-to-analog converter which is responsive to the synthesis circuit to provide the 38 KHZ carrier signal. The 19 KHz pilot subcarrier signal is generated by a digital-to-analog converter that is clocked by a crystal timer which is common to both signals thereby to lock the phase of the pilot signal to the 38 KHz signal.

Abstract: A two-tone test signal method for calibrating a BTSC monitoring system compensates for errors introduced into the monitoring system by unpredictable high frequency components of noise when testing the low frequency performance characteristics of the monitoring system. The two-tone test signal has a low frequency tone and a lower level high frequency tone which overrides the high frequency component of noise. The two-tone test signal is synthesized according to the BTSC specification to produce a "perfect" left-only signal for both tones.

Abstract: An adapter is provided for use with a television receiver to detect and decode stereophonic audio signals, SAP signals or auxiliary signals that may be transmitted with the composite television signals. The adapter includes an IF input that is physically separate from the television receiver for receiving IF audio signals that normally are derived from the transmitted composite telephone signals. Detecting circuitry is coupled to the IF input by means of a tuned circuit that is tuned to the IF carrier frequency of the received IF audio signals for detecting the stereo, SAP or auxiliary signals transmitted with the composite television signals. The detected signals are used to drive utilization means, such as loudspeakers. Preferably, switches are provided to select the stereo or SAP or auxiliary signals for detection.

Abstract: An instrument for testing the multichannel sound circuits of a television receiver provides a plurality of discrete test signals respectively consisting of a carrier sine wave modulated with an audio frequency sine wave having an amplitude and phase which matches the MTS encoding formula.

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 circuit serves to extract one of two or more pilot tones which are modulated on an audio-frequency signal to select an appropriate decoder, and which cause a changeover to the appropriate decoder or of a decoding signal processor. To this end, one of the stereo signals is digitized by means of a clocked analog-to-digital converter, and the audio signal is separated from the pilot-signal-containing component by means of a pilot-tone-range filter and then averaged over a number of clock periods of the analog-to-digital converter by means of a sampling averager. The output signal of the averager is applied to the inputs of pilot-tone filters, then rectified to measure the signal energy, and applied to the inputs of low-pass filters. The outputs of the low-pass filter control a logic circuit which causes the two audio-frequency signals to be applied to the input of the appropriate decoder.

Abstract: A synchronizing circuit used for both an AM intermediate frequency signal and an FM composite signal. A phase detector, voltage-controlled oscillator, frequency divider and phase shifter are connected in a phase-locked loop. The division factor of the frequency divider is controlled to different values for the AM and FM signals.

Abstract: A TV SAP/stereo audio system includes a DC switch for selectively coupling the output of a stereo decoder and the output of a SAP detector to a stereo amplifier. A DC voltage, representative of the SAP carrier level, is developed and applied to a pair of threshold transistors. The lower threshold transistor is driven conductive when the DC voltage is below a first voltage and the upper threshold transistor is driven conductive when the DC voltage is above a second voltage. The threshold voltages are established by a pair of voltage dividers. A SAP control transistor is coupled to the collectors of the threshold transistors and is driven conductive when either threshold transistor is in conduction. The SAP control transistor is connected to the DC switch and prevents coupling of the SAP detector output to the stereo amplifier when it is conducting.

Abstract: A digital transmission system using standard FM broadcast stations employs an SCA subcarrier which is amplitude modulated with a second subcarrier modulated to have different phase orientations representative of digital data. Bits are separated from a digital data stream in groups and are differentially encoded into one of at least four phase orientations of the second subcarrier. The amplitude modulated SCA subcarrier is combined with the stereo signal output of a stereo multiplexer to form the modulating signal for the station FM modulator. The receiver includes a differential phase detector for reconstruction of the differentially encoded digital data.A system which additionally includes means for modulating the SCA subcarrier with a composite signal having an audio signal in addition to the differentially encoded second subcarrier is disclosed.

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: A circuit has two signal paths. The first path provides a signal with a selected magnitude and phase. The second path selectively provides either no signal or a signal with twice the magnitude and opposite phase with respect to that provided by said first path. The signals of the two paths are combined to provide a signal with a selectable phase. The circuit can be used in a stereo decoder in which an L+R stereo sum signal is combined with an expanded R-L stereo difference signal, provided by an expander also used for a SAP signal, to produce left (L) and right (R) stereo signals so that when the SAP signal is being reproduced, it is of the same phase in both left and right channels.

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: A simple digital filter having only a single multiplier operates to extract the pilot tone from a demodulated and digitized FM stereo signal. The number of poles in the filter is chosen so that the filter output is also usable to produce a digitized representation of the carrier tone for the left minus right stereo channel. This signal is in turn used to decode the input representation into the desired left and right channel signals. The circuit of the present invention is particularly amenable to fabrication on an integrated circuit chip.

Abstract: An approximately sinusoidal signal is generated by superimposing a first signal, which has a half cycle duration and corresponds to a triangular signal which is suppressed during every second half cycle, on a second triangular signal, every second waveform of the superimposed signal thus obtained being inverted.

Abstract: A radio communication system includes a transmitter unit, a radio transmission line and a receiver unit. The transmitter unit contains an insertion circuit for inserting one or two signals for carrier recovery into a modulated wave signal. Each signal for carrier recovery has a frequency (f.sub.O +f.sub.CL), where 0<.vertline.k.vertline.<1. The receiver unit receives, via the radio transmission line, the modulated wave signal, provided with the signals for carrier recovery therein. The receiver unit recovers, from the received signal, the frequency components f.sub.O and f.sub.CL and thereby reproduces the original data signal supplied to the transmitter unit with the use of the thus recovered frequency components f.sub.O and f.sub.CL.

Abstract: FM transmission system in which, besides program content, an auxiliary carrier of, for example 57 kHz, is radiated, which auxiliary carrier is modulated by an announcement recognition (AR) signal and by a region or radio-station recognition (RR) signal, the AR and RR signals being low-frequency, AM modulations on the auxiliary carrier. To enhance recognition of an AR signal, e.g. between 142 and 170 Hz, is enhanced, in spite of reception difficulties, for example due to multi-path reception and the like, by decreasing the modulation of the 57 kHz subcarrier by the RR signal to 30% or less, while the AR signal is modulating the subcarrier, so that the AR modulation may extend to 60 and even 90% modulation. Multiple AR frequencies can be used, for example to characterize different announcements, e.g. in different languages, or of different characteristics, such as traffic, news, sports, or others, recognition of the AR signal in the receiver permitting switch-over from other reproduced programs, e.g.

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: FM-receiver including a frequency-locked loop (2-14), which loop includes, successively connected, a voltage controlled oscillator (8), a mixer circuit (2) connected to an aerial input, an IF-portion comprising an IF-filter (9), an FM-detector (4), a loop filter (5) and a loop amplifier (6) for adjusting the transfer characteristic of the frequency locked loop (2-14), which loop amplifier (6) is connected to a control input of the voltage-controlled oscillator (8) for a feedback of the modulation signal of the received FM-signal. The loop filter (5) comprises a first low-pass filter (14). The FM-receiver being realizable in integrated circuit form and suitable for processing FM-stereo signals. The receiver is at least comparable to conventional FM-stereo receivers as regards selectivity, harmonic distortion and stability, the conventional FM-stereo receivers not being realizable in integrated circuit form.

Abstract: A triphonic sound system in which three independent stereophonically related audio frequency source signals L, R and C are combined to derive three other audio frequency signals M, S, and T which respectively comprise (L+1.4C+R, (L-R) and (-1.4C). In a preferred transmitter embodiment, useful in television broadcasting, the audio signals S and T modulate two quadrature-related sub-carriers of the same frequency to develop two double-sideband, suppressed-carrier signals, the frequency of the subcarriers being sufficiently high as to assure a frequency gap between the lower sidebands of the modulated subcarrier signals and the audio frequency signal (L+1.4C+R). The aforementioned signals, and a pilot signal having a frequency which lies within the frequency gap, are combined and frequency-modulated onto a high frequency carrier for the purpose of transmitting the same to one or more remote receivers.

Abstract: First and second rectangular signals which are 90.degree. out of phase with each other are derived by comparators and an RS flip-flop from a symmetrical triangular wave signal. The first rectangular signal is halved in frequency by a frequency divider, the output of which is supplied to an adder. The second rectangular wave signal is also delivered to the adder. An output from the adder is converted by a bandpass filter into a sine-wave subcarrier signal in synchronism with a stereo pilot signal in an FM stereo tuner. The first and second rectangular signals may be derived by a pair of D-type flip-flops from a pulse signal.

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: An FM broadcasting system comprises an FM transmitter for transmitting a multiplex signal which is frequency-modulated on a main carrier wave and an FM receiver for cooperation with said FM transmitter. The multiplex signal comprises: an audio-frequency first information signal and, in the case of a stereo transmission, a second information signal modulated on a suppressed stereo subcarrier, a stereo pilot signal whose frequency (f.sub.p) is situated between the frequency spectra of the two information signals, a first binary-code signal (f.sub.p -f.sub.c) which is phase-modulated on a first code subcarrier situated outside the frequency spectra, which code subcarrier is a harmonic of a subharmonic of the stereo pilot (f.sub.p) which harmonic does not coincide with a harmonic of said pilot (f.sub.p), the multiplex signal, in order to extend the transmission capacity, comprising a second binary-code signal which is phase-modulated on a second code subcarrier (f.sub.p +f.sub.c).

Abstract: An FM stereophonic radio broadcasting system in which stereophonically related audio frequency source signals L and R are matrixed to obtain stereophonic sum and difference signals M and S, respectively. At the transmitter, the difference signal, is compressed, and the conventional difference signal and the compressed difference signal modulate respective quadrature-related sub-carriers of the same frequency to develop two double-sideband, suppressed-carrier signals, the frequency of the sub-carriers being sufficiently high as to assure a frequency gap between the lower sidebands of the modulated sub-carrier signals and the sum signal M. The M signal, the aforementioned suppressed-carrier signals, and a pilot signal having a frequency which lies within the frequency gap, are combined and frequency-modulated onto a high frequency carrier for the purpose of transmitting the same to one or more remote receivers.

Abstract: An FM broadcast band demodulator and stereo decoder which can be connected to an existing frequency modulated, or FM broadcast tuner or receiver. The unit includes four basic sections; FM demodulation, stereo decoding, audio amplification, and tuning error detection. The FM demodulation is done by an integrated circuit directly coupled to a second integrated circuit which performs the stereo decoding function. The function output signals of the second integrated circuit are re-centered to a direct current or d-c level of zero by voltage dividers and amplified by operational amplifiers to drive a load. The tuning error indicator is connected between the first and second integrated circuits and nullifies the d-c components from the output signal of the first integrated circuit before integrating the output signal to remove the audio portion and leave only an average d-c component. The remaining d-c signal is amplified and applied through a bridge rectifier to a light emitting diode or LED.

Abstract: A system and method for transferring digital data via the sub-carrier of a commercial broadcast FM radio station. Digital data generated by an originating subscriber is shaped with substantially a raised cosine response in the time domain. The shaped signal is then pre-emphasized and used to frequency modulate (direct angle modulate) a sub-carrier. The sub-carrier in turn frequency modulates the carrier and the data is transmitted by the radio station along with its commercial program. A receiving subscriber detects the sub-carrier and decodes and displays the originated data.