Abstract: A converter is coupled between the antenna and the RF stage of an FM stereophonic receiver to convert received AM stereo signals into FM stereo signals. A received AM stereo signal is translated to an IF signal, and decoded into two stereo signals. These signals are then encoded into a broadcast-type FM stereophonic signal which is coupled into the front end of an FM stereo receiver.

Abstract: In the field of AM stereo detection, co-channel or adjacent channel interference may cause some distortion and side-to-side movement of a stereo signal source as well as false "stereo detect" signals in AM stereo receivers having phase locked loop (PLL) systems. The invention provides a filter receiving the incoming signal and passing only the frequencies resulting from said interference; a sensor measures the output of the filters and if this signal is above a given level, the monophonic mode is enabled, i.e., the pilot detector, the stereo presence indicator and the stereo mode switch are disenabled for a timed interval. A higher given level of interference is required for stereo disenablement when stereo transmission with pilot tone is already being received.

Abstract: For the simplified text or picture data signal transmission through a broadcasting system, an additional phase and/or frequency modulation is produced in amplitude modulated transmitters. In a preferred but relative slow transmission system, a frequency modulation (f.sub.1 -f.sub.n) occurs in a band width of .+-.25 Hz, whereby the transmitted quality of the simultaneously transmitted broadcast does not suffer. Depending on the type of transmission means, equipment and frequency (f.sub.o) of the carrier wave (T), this band width can be increased, for example during text transmission, in order to achieve a higher transmission speed. The system is compatible with AM mono and stero equipment as well as with printing and display installations of the electronic data processing and communication technologies.

Abstract: An amplitude limiter for an AM broadcast transmitter to minimize energy in the broadcasted signal outside an allocated broadcast bandwidth. The secondary and higher order spectra (i.e. second and higher harmonics) of a broadcasted AM stereophonic signal are minimized by limiting the amplitude of the audio signal, prior to modulation onto the carrier, within a predetermined portion of the audio frequency range. This is achieved by controlling the gain of the audio signals in that predetermined portion as a function of the level of a submodulation component also within that predetermined portion of the audio frequency range.

Abstract: In a radio receiver including a demodulating circuit with monaural and stereophonic modes for respectively demodulating a monaural broadcast signal having a carrier amplitude modulated with a monaural signal and demodulating an AM stereophonic broadcast signal having a carrier modulated with the sum and difference of right- and left-channel stereophonic signals and with a relatively low frequency pilot signal, and a tuning section operable for tuning the receiver to receive a broadcast signal whose carrier has a selected frequency; a filter is effective to extract the pilot signal from the received broadcast signal when the latter is an AM stereophonic broadcast signal and the stereophonic mode of the demodulating circuit is established in response to the extracted pilot signal, a disturbance signal generated upon operation of the tuning section or in response to external noise and which is in a frequency range near to the frequency of the pilot signal so as to be possibly extracted with the latter, and there

Abstract: In a receiver for composite amplitude and angle modulated signals and having a non-flat automatic gain control characteristic, there is provided apparatus for providing distortion correction to the quadrature component produced by the angular modulation in accordance with the amplitude modulation component. In accordance with the invention, the output of an amplitude demodulator is modified to remove the carrier signal level dependent magnitude multiplier and develop a modification signal which is used to inversely amplitude modulate the quadrature signal component to provide distortion correction over a range of carrier signal levels. Such inverse modulation can be provided before or after quadrature demodulation of the received signal.

Abstract: The method and apparatus for providing an AM stereo receiver suitable for receiving an AM/PM modulated RF carrier frequency, the receiver uses a standard AM detector to receive said AM/PM modulated intermediate frequency and to provide an 1+r signal. The stereo detector system further provides an 1-r signal and comprises means (104) for receiving and limiting the amplitude of the AM/PM modulated signal to eliminate the amplitude modulation therefrom and for providing a signal having phase modulation only. The limited AM/PM signal from limiter (104) is then provided to an FM quadrature detector (106) for recovering any PM signal. The PM signal detected and provided by said FM quadrature detector (106) is then integrated by an integrator (124) to provide a true PM signal. The output of integrator (124) is provided to a squelch gate (128) and to a means for sampling and determining the presence of a 5 Hz signal.

Abstract: An AM stereophonic signal transmitter includes a matrix circuit which generates a sum signal corresponding to the sum of left and right channel stereophonic signals and a difference signal corresponding to the difference between the left and right channel stereophonic signals; a first phase shifting circuit which phase shifts the sum signal by -45.degree.; a second phase shifting circuit which phase shifts the difference signal by +45.degree.; a sub-modulator which modulates the phase-shifted difference signal by the phase-shifted sum signal to produce a first modulated output signal having the form Y.sub.+ (1+m.sub.t X.sub.-), where X.sub.- represents the phase-shifted sum signal, m.sub.t represents the modulation factor of the sub-modulator and 1 represents a carrier component; a modifying circuit for modifying the phase-shifted sum signal to produce a modified signal having the form .sqroot.(1+X.sub.-).sup.2 -Y.sub.+.sup.2 (1+m.sub.t X.sub.-).sup.2, where Y.sub.

Abstract: A multi-function sound system including an AM stereophonic receiving function in which interference with operating circuits in modes other than the AM stereophonic mode is eliminated. A limiter receives a IF AM stereophonic received signal and removes the amplitude variation components therefrom and couples the resulting signal to a phase detector composed of a phase-locked loop which produces as an output signal a sub-signal. A switch is provided which deactivates both the limiter and the voltage-controlled oscillator in the phase-locked loop circuit when the sound system is set to other than the AM stereophonic receiving mode.

Abstract: A circuit for processing an angle modulated signal having amplitude modulation signal components in stereophonic broadcasting systems. An inverse modulation of a signal to be detected is provided over a first signal amplitude range, and a constant signal level is provided over a remaining range for signals having a marginal amplitude level. The discontinuity in the control range avoids noise expansion for high negative amplitude modulator levels for the signal to be angle modulated.

Abstract: An AM stereo broadcasting system for transmitting stereo signals in the AM broadcasting band. The system is based on amplitude modulation by two carriers having the same frequency and a 90.degree. phase difference from each other, and is capable of increasing the modulation depth of pilot signals (used for stereo signal identification) irrespective of the stereo signals, so that the pilot signals can be easily detected. By modulating both the sum and difference signals by the pilot signal, the receiver portion of the present system can derive the pilot signal irrespective of the stereo signals, thereby obviating many of the previous AM stereo broadcasting system problems.

Abstract: In an AM radio signal receiver, the value of Q of the input tuning circuit is varied in accordance with information indicative of the magnitude of the received signal. This information may be derived from the intermediate frequency (IF) signal processing stage of a superheterodyne receiver. In such a case, the IF signal is applied to a narrow-band filter having a pass band which is narrower than that of the IF signal processing stage. The amplitude of the output signal from the narrow-band filter is then detected to control a variable resistance element which is connected in parallel with winding of an input tuning coil so that the value of Q of the input tuning circuit is lowered when receiving a broadcasting signal having relatively high intensity. The invention may be adapted to an AM stereo receiver. In this case, the variable resistance element is controlled by both a signal indicative of the amplitude of the received signal and a signal indicating that the received signal is a stereo signal.

Abstract: Apparatus is disclosed for use in improving the separation between the individual channels of a plural channel communication system such as a stereo AM radio broadcasting system. The separation corrections are made to the baseband signals. Two sources (14, 16) provide input signals to a matrix circuit (18) which generates sum and difference signals therefrom. A circuit (44) adjusts the phase of the difference signal relative to the sum signal. The circuit (44) includes phase shifting circuits (50, 52) which provide two difference signals phase shifted by ninety degrees relative to one another. The two signals are combined in a signal adder (54). The degree of phase shift provided by the circuit (44) is selectively adjusted by varying the gain of gain circuits (46, 48) included in the paths of the two difference signals. Means (42, 44) are included for varying the gains of the input signals to the difference signal. The gain factors are frequency dependent in some embodiments.

Abstract: A stereo demodulating circuit for an AM stereo receiver includes an IF stage for producing an IF signal from a received AM stereo signal of the type having a carrier amplitude-modulated with the sum of left and right channel signals and the carrier phase-modulated with the difference of the left and right channel signals; an envelope detector for producing a sum signal corresponding to the sum of the left and right channel signals in response to the IF signal, and having level information, amplitude-modulation information and a DC component; a negative peak limiter for limiting the minimum level of the sum signal from the envelope detector; a divider for dividing the IF signal by the sum signal with its minimum level limited to produce a phase-modulation signal; a phase-locked loop for producing a non-modulation signal from the IF signal; a low-pass filter for removing the amplitude-modulation information from the sum signal from the envelope detector to produce a level information signal having only the leve

Abstract: A receiver for demodulating a stereophonic broadcast signal. Envelope detection is provided for a preselected radio frequency broadcast signal. Angle demodulation of a difference signal contained in the broadcast signal is provided at the radio frequency level avoiding the use of superheterodyne techniques. Improved linearity is achieved over detection techniques which operate at an intermediate frequency level. Receiver protection from excessive negative modulation peaks is provided as well as subsequent audio signal processing.

Abstract: A stereo receiver is described which is capable of receiving any two or more of the five currently proposed AM stereo system broadcast signals. The multisystem receiver includes circuitry which is used in various configurations to demodulate the stereo signal components from broadcast signals of any one of two or more of the proposed systems. Selection of appropriate elements of the receiver's circuitry for demodulating any one of the received signals is performed automatically in response to the detection of the presence of a corresponding pilot signal which is unique for each of the five different AM stereo systems that have been proposed. The receiver includes apparatus which detects the presence of such pilot signals and controls the automatic switching of such receiver circuitry. Also described is the application of such apparatus for reliably detecting the presence of the desired pilot signal in a single system stereo receiver.

Abstract: Multiple low frequency tones are employed for stereo indication in an AM stereo radio system. The tones are modulated on a carrier wave which is also multiplex modulated by stereo related audio signals. Detection of the presence of one of the tones in a received signal provides an indication of the possibility of stereo related modulation components in the received signal. Detection of the presence of both tones in the received signal provides confirmation that stereo related modulation components are in the received signal. In a preferred embodiment, 15 Hz and 30 Hz phase-related tones are used. A stereo receiver incorporates 15 Hz and 30 Hz phase detectors which form interrelated phase-locked loops with a 30 Hz reference oscillator. The presence of both tones in the proper phase relationship indicates reception from an AM radio station which is broadcasting in stereo.

Abstract: A low frequency tone detector filters out undesired frequencies in a received signal, than a latching circuit locks on when a given number of low frequency cycles are detected, having at least a predetermined peak amplitude. Thereafter, only a second given number of missing or low amplitude cycles will reset the latch. When the detector determines that the received signal is weak or of very poor quality, false detect signals are essentially prevented. The circuit is particularly suited to use with AM stereophonic signals where a low frequency tone is added to the difference channel for providing mono/stereo indication and mode switching.

Abstract: A multiplexed signal receiver is arranged such that two independent signals are multiplexed on a single carrier by amplitude and frequency modulation or amplitude and or phase modulation. The multiplexed signal receiver includes a balanced type amplitude limiter and two double balanced type product detectors for amplitude and frequency or amplitude and phase demodulation. The receiver uses the direct coupling between said amplitude limiter and the two product detectors to facilitate the circuit integration thereof on a monolithic semiconductor chip.

Abstract: An AM stereophonic receiver including a stereophonic pilot signal eliminating circuit which substantially completely eliminates a pilot signal in an input stage of a matrix detector. A received AM stereophonic signal, of the type in which the carrier signal is phase-modulated with a sub-signal and amplitude modulated by a main signal, is coupled to a main signal detector and a sub-signal detector. The output of the sub-signal detector is coupled through a band amplifier which produces as an output a signal corresponding to the pilot signal contained in the stereophonic signal. The outputs of the sub-signal detector and main signal detector are coupled to inputs of adder/subtractor circuit in a matrix detector while the output of the band amplifier is also coupled thereto in a phase so as to cancel the pilot signal contained in the output of the sub-signal detector.

Abstract: An AM-FM receiver which uses the FM-demodulator for demodulating the phase modulated sidebands of an AM-stereo signal. Therefore, it has to operate as a FM-demodulator also at the AM-intermediate frequency which is achieved by means of a parallel resonant circuit tuned to the AM-intermediate frequency (455 KHz) and arranged in series with a parallel resonant circuit which is tuned to the FM-intermediate frequency (10.7 MHz). The FM-demodulator is followed by an integrating circuit which only becomes operative in the event of AM-reception and which forms a phase demodulator in conjunction with the FM-demodulator. The additional costs and efforts for the reception of AM-stereo signals is therefore extremely small. In addition to the components which are already required in an AM-FM radio receiver only a further parallel resonant circuit and an integrating circuit are required.