Abstract: An apparatus for modulating signals for use in AM stereo transmission having left and right signal inputs feeding respective inverted and non-inverted inphase modulators and respective inverted and non-inverted quadrature modulators. The inverted and non-inverted inphase outputs are summed, the inverted and non-inverted quadrature outputs are summed, and the resulting inphase and quadrature signals are summed. The resulting signal is fed to a limiter and then to a broadcast transmitter, such as a difference transmitter, as a radio frequency input.

Abstract: A stereophonic transmitting system is disclosed for transmitting in quadrature a single carrier signal carrying first and second signals. The transmitting system comprises a phase shifter or modulator for phase shifting a carrier signal of a frequency fc in accordance with a feedback signal to provide a phase shifted carrier signal. A first detector operates to detect a component of the phase modulated carrier signal in phase with the carrier signal to provide an in-phase signal and a second detector to detect a component of the phase modulated carrier signal out-of-phase with the carrier signal to provide a quadrature signal. A first multiplier multiplies the in-phase signal by the first signal to provide a first multiplied signal and a second multiplier multiplies the quadrature signal by the second signal to provide a second multiplied signal. A difference circuit is provided for obtaining the difference between the first and second multiplied signals to provide the feedback signal to the phase shifter.

Abstract: An AM stereo transmitter with bandwidth limiting utilizes the detection of high frequency energy in the modulating signal to control the difference channel input to the stereo encoder.

Abstract: An improved transmitter for a compatible independent sideband (ISB) AM stereo system develops a phase modulated carrier where the modulation represents the stereo difference signal inverse modulated by the stereo sum signal in accordance with a selected modulation function. The phase modulated carrier then is amplitude modulated by the stereo sum signal. This simplified modulation scheme provides the second-harmonic sideband correction required to develop a true single sideband type signal wherein left and right stereo information are transmitted in separate lower and upper sidebands, which can be demodulated without distortion in ISB AM stereo receivers. Simplified receivers which use inverse modulation are also disclosed.

Abstract: An amplitude modulated radio transmission system is described which is compatible with conventional AM receivers. The transmitted signal comprises a carrier and two unequal amplitude sidebands. This signal can be received by receivers that are tuned to the carrier as well as receivers that are off tuned to favor the stronger sideband.

Abstract: An AM stereo modulator is disclosed which includes a limiter responsive to first and second audio signals for providing first and second equally limited amplitude limited signals. A quadrature amplitude modulator responds to the first and second amplitude limited signals and provides an amplitude modulated carrier signal having in-phase and quadrature-phase components modulated in accordance with the first and second amplitude limited signals, respectively. A distortion detector monitors the envelope of the quadrature amplitude modulated signal for detecting the extent to which the envelope differs from one of the two amplitude limited signals and for controlling the limiter in accordance with the extent of the difference. The distortion detector can also be used to control quadrature channel signal gain instead of the limiter. A program analyzer determines whether to control quadrature channel signal gain or the limiter with the distortion detector.

Abstract: A method for generating a compatible AM quadrature stereo wave by delivering a modulated carrier with in-phase sidebands generated by a first combination of two signals, and quadrature sidebands generated by a second combination of the signals, the in-phase and quadrature sidebands having substantially the same maximum amplitude. The carrier and both sets of sidebands are delivered to an envelope detector, which delivers only the first combination of signals, undistorted by the presence of the quadrature sidebands. The carrier and both sets of sidebands are also delivered to a synchronous detector, which delivers only the first combination of signals with predistortion. The output of the synchronous detector is subtracted from the output of the envelope detector to obtain as a result the predistortion of the first signal combination due to the presence of the quadrature sidebands.

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: 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: A system for time-period modulating (TPM) a subcarrier in accordance with the amplitude of an input signal includes generating a ramp signal of constant slope, comparing the ramp signal with the input signal, and resetting the ramp signal when the ramp signal reaches the input signal. Each time the ramp signal is reset, a clock pulse is counted. These clock pulses are counted in cyclic groups of N. After each clock pulse is counted, the then attained count is converted to a value of a sinusoid about some reference. The values for each of N counts define one sinusoidal cycle of the modulated subcarrier. Converting these values to voltage levels produces a sinusoidal stepwave which has a period linearly proportional to the amplitude of the input signal at the time.

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: 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: 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.