U.S. Philips Corporation

Johan M Schmidt

Johannes O Voorman

Theodoor A Claasen

Johannes Bernhard Peek

Gerardus C Gielis

Henri J Van Der Heide

Harry B Schoonheijm

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). The carrier wave information of the two code subcarrier waves can be identified in a simple way by selecting their frequencies to be symmetrical about the stereo pilot signal or its harmonic (3f.sub.p) and by selecting the phase angle between the sum of the two code subcarriers and the stereo pilot or the relevant harmonic thereof to be situated at preferably an integral multiple of .pi./4.

FM Broadcasting system with transmitter identification

FM-broadcasting system comprising a FM-transmitter (1-16, 32-34) and a receiver (14-31, 35, 36) cooperating therewith, the transmission signal of which comprises a multiplex signal which is frequency-modulated on a main carrier wave, which multiplex signal comprises an audio-frequency information signal (L+R) and, in the case of a stereo transmission, a stereo information signal (L-R) modulated on a (38 kC) suppressed stereo subcarrier wave, also comprising a (19 kC) stereo pilot which is situated between the frequency spectra of the two information signals and a binary, differentially coded code signal which is phase-modulated on a (16.625 kC) code subcarrier wave which is situated outside the frequency spectra, and does not coincide with the (19 kC) stereo pilot, the receiver (14-31, 35, 36) comprising a pilot regeneration circuit (22-25) for regenerating the (19 kC) stereo pilot, the code signal having a bit repetition period which is an integral number of times the period of the (19 kC) stereo pilot. The signal delay (.tau.) required for differentially decoding the code signal is stabilized by a clock signal derived from the (19 kC) stereo pilot, use then being made of the fixed frequency relationship between the bit frequency of the code signal and the stereo pilot frequency, so that disturbances due to variations in the signal delay are avoided.

FM-broadcasting system with transmitter identification by binary

An FM-receiver with transmitter characterization, having a tuning unit, an IF-amplifier, a demodulation circuit for demodulating a discrete transmitter characterization signal, a clock regeneration circuit, a decoding device for decoding the discrete transmitter characterization signal and a signal processing unit. The clock regeneration circuit regenerates a clock signal the period of which is obtained by dividing the frequency of the stereo pilot signal. Synchronization of the clock signal phase with the phase of the clock signal used in the transmitter is carried out by detecting, using of a periodic window signal, the average phase of the code edges in the discrete transmitter characterization signal and by choosing the phase of the regenerated clock signal to be equal thereto.

FM-Receiver with transmitter characterization

FM radio broadcasting system with transmitter identification by means of a transmitted subcarrier whose frequency is a harmonic of subharmonic of the stereo pilot and which is binary phase modulated with transmitter identification signals. In the transmitter the subcarrier is locked to the stereo pilot and the unmodulated wave, which is required for detection of the transmitter identification signal, is derived in the receiver from the received stereo pilot.

Radio broadcasting system with transmitter identification

FM radio broadcasting is disclosed with code signalling by means of a subcarrier wave in the free frequency range around the stereo pilot on one side of said pilot (or of two subcarrier waves in said frequency range on both sides of the stereo pilot). The subcarrier wave, which is derived from the stereo pilot on the transmission side, is binary phase-modulated with the code signal, and is detected on the reception side with an unmodulated wave which is derived from the received stereo pilot.

Radio broadcasting system with code signalling

A circuit for suppressing pulse-shaped interferences in an audio signal caused by scratches on a phonograph disc, comprising a signal processing section connected between an audio frequency input and an audio frequency output, comprising a noise suppressor having a control input; as well as a control signal section connected between the audio frequency input and the control input, said control signal section comprising a first threshold selection circuit connected to the audio frequency input for selecting pulse-shaped signals from the audio signal, followed by a second threshold selection circuit for distinguishing the pulse-shaped signals originating from noise signals from those originating from musical signals.

Circuit for suppressing noise caused by scratches on a phonograph record

A signal consisting of square pulses is applied to an FSK transmitter and is transformed into a control signal consisting of substantially symmetrical trapezoidal pulses. This control signal is applied on the one hand to a gyrator oscillator modulator to generate an FSK signal and on the other hand to a conversion device which converts the control signal into a direct voltage signal the direct voltage value of which shows a positive pulsatory variation each time during the occurrence of the edges of the trapezoidal pulses of the control signal. Said direct voltage signal is used to subsequently modulate the FSK signal in an amplitude modulator. The amplitude-modulator FSK signal may now be applied directly as a modulation signal to a carrier modulator without the intermediary of a band-pass filter.

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Eindhoven, Netherlands

Johan M Schmidt