Abstract: A satellite communications system with improved intermodulation distortion characteristics as the result of incorporating distortion reduction circuitry in the down-link receiver but which is controlled by the up-link transmission equipment.

Abstract: A system for preventing the unauthorized copying of audio or video recording by (1) processing the recorded material so as to identify the protected material in a manner that does not audibly distort the program material, and (2) processing the recorded material by a second method that produces audible artifacts. Equipment capable of removing the audible artifacts while retaining the inaudible identification signal would be installed in audio digital tape recorders or video recorders so as to allow the equipment to be used for playback purposes while at the same time discouraging the unauthorized copying of audio, video or motion picture protected material.

Abstract: Stereo decoders for use in AM stereo receivers are disclosed which have two different modes of operation, one of which suffers adverse effects from the presence of co-channel interference and employs envelope detection to develope an (L+R) representative signal. When such interference is detected the decoder switches to a second mode of operation, which is less affected by the interference, and also switches to synchronous detection to develop the (L+R) representative signal.

Abstract: A synchronous transmission system that improves reception in areas where the main and the satellite signal create significant self interference. At least one of the synchronous transmitters is phase modulated in accordance with a selected modulation function which varies at a sub sonic rate.

Abstract: Asymmetrical sideband amplitude modulation (AM) stereo transmission apparatus which transmits left (L) plus right (R) stereo information (L+R) in one stereo channel and a signal including L-R stereo information in a second stereo channel. Benefits include significant reduction of modulation envelope distortion in null regions of the transmitter's antenna radiation pattern and improved quality of reception in the presence of adjacent channel and co-channel interference, easing of the difficulty in tuning continuously tuned receivers and improvement of the fidelity of such receivers when side tuned, while at the same time providing a signal which, when received and decoded by an independent sideband AM stereo receiver, provides pleasing stereo effects.

Abstract: An improved transmitter having protection from undesired out-of-band radiation caused by high frequency components in a supplied signal to be transmitted uses means for determining when the supplied signal is such as to cause out-of-band radiation. A resulting control signal then reduces the amplitude of the higher frequency components of the supplied signal relative to the remainder of the signal, thereby preventing out-of-band radiation.

Abstract: Reduction of undesired r.f. harmonics, generated in the highest power power amplifier of a transmitter, is achieved by providing at least one alternate path for the undesired harmonics incorporating a relatively low powered power amplifier for at least one undesired harmonic component and causing the harmonic, in this alternate path, to have an amplitude that is substantially equal and a phase 180 degrees relative to the corresponding harmonic output from the main path and combining the outputs of the paths.

Abstract: An improved asymmetrical sideband amplitude modulation (AM) transmitter is provided wherein the resulting transmitted signal produces a pleasing pseudo-stereo effect when received by a stereo receiver of the type designed to receive symmetrical sideband, phase-separated AM stereo radio braodcasts, when such receiver is operating in its stereo mode.

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: A system for transmitting a composite signal comprising a data transmission signal component and an AM broadcast signal component. The broadcast signal component may be monophonic or stereophonic. The level of the data signal component is made a function of the modulation level so that the data signal is masked by the program modulation and, therefore, AM radio listeners will not be disturbed by the data signal. The rate of data transmission, in one embodiment, is reduced as the level of the data signal is reduced. The data signal is in quadrature with the AM carrier so as to minimize detection of the data signal by an envelope demodulator. Suitable data receivers are also disclosed.

Abstract: Certain, but not all AM stereo radio broadcasting and reception systems suffer from a severe form of reception anomaly wherein the perceived stereo image moves from side to side, back and forth, which effect has come to be known as "Stereo Platform Motion" or simply "Platform Motion". A prior art patent proposed a method for sensing reception conditions conductive to Platform Motion and then switching the receiver from stereo to monophonic reception to avoid Platform Motion. The present invention enables the AM stereo receiver to maintain stereo operation under such reception conditions, and instead of switching the receiver to monophonic operation, it switches the receiver to a different method of stereo reception that does not suffer from Platform Motion.

Abstract: Disclosed is an AM stereo receiver capable of receiving signals representing at least two different types of AM stereo systems, but using an integrated circuit (IC) decoder designed to properly decode received signals representing only one of the two types of systems. The receiver includes circuitry coupled to the IC which adapts the IC for also properly decoding received signals representing the second type of AM stereo system as well. Circuitry is also disclosed for automatically detecting which type of AM stereo system is being received and for configuring the receiver's decoding circuits to properly decode the received stereo signals.

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: A stereo speaker system is shown having at least three individual speakers arranged along a path, with one of the speakers positioned between the other two speakers and connected to receive signals from a selected one of a pair of left and right signal outputs from a stereo signal source such as a stereo radio. Both of the other two speakers are connected to receive signals from the remaining one of said pair of outputs. Balanced stereo images are thus obtained simultaneously at two different locations. The system has particular application in an automobile. Another embodiment is shown which uses more than three speakers.

Abstract: A system and method for squelching noise and storing messages. Many receiving systems produce noise bursts at the end of the reception of a message and prior to the operation of the muting circuit. Such noise bursts are especially severe in frequency modulation systems using limiters. By delaying the audio signal until the squelch circuit's hang time is completed the noise bursts are muted.One application of this invention is in vehicles such as police cars and taxicabs. For such an application one of the essential parts of almost every message is the street address where the vehicle is needed. Since it is easy to confuse addresses, and thereby require a repeat of the message, a recording of at least the address portion of the message would be most useful. A storage system is provided in order to allow the repetition of messages.

Abstract: An improved high efficiency amplitude modulation system comprising three power amplifier paths, each incorporating high efficiency type amplifiers.One path amplifies an unmodulated carrier wave and the other two amplify phase modulated waves preferably generated by the disclosed improved Armstrong phase modulator.

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: A radio transmission system of the suppressed carrier type incorporating means for correcting frequency errors. The transmission circuit can include the usual components which first produce a carrier wave, an upper sideband, and a lower sideband. The carrier wave and one of the sidebands are eliminated and only the desired sideband is radiated. The transmitter also incorporates a highly selective circuit which substantially reduces the amplitude of all audio frequencies below about 350 hertz. This frequency characteristic is used as a frequency reference to regenerate the carrier wave in the receiving system. Since low frequencies of 350 hertz are not present in voice waves at all instances, a storage circuit is employed to store a control voltage during the absence of low frequency sounds which would have the identifying frequency step.

Abstract: An apparatus for generating a composite AM stereo broadcast signal wherein a carrier is angle modulated with stereo difference information contained in a first supplied signal and the angle-modulated carrier is then amplitude modulated with stereo sum information contained in a second supplied signal, an improvement wherein distortion is predicted by the use of a simulated transmitter and receiver to generate a correction signal having distortion representative components. Correction signals developed in this manner are used to modify the angle-modulated signal utilizing a feedback technique, a subtractive technique, or both, thereby reducing distortion in the output of the stereo difference signal channel of actual AM stereo receivers which receive said composite AM stereo signal.

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 configuration 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.