Abstract: A method and apparatus is disclosed for automatic elimination of frequency instabilities in a receiver frequency converter. Such instabilities result from temperature variations and mechanical vibrations of the local oscillator of a first stage converter. A marker signal is introduced into the first stage down converter mixer and is subjected to the same variations in frequency conversion as is the received signal from an antenna. Intermediate down converted received signals and an intermediate down converted marker signal are received by a second stage converter where such signals are applied to a mixer, the output of which is free of frequency variations introduced by the local oscillator of the first stage converter.

Abstract: A simulcast system (100) having remote sites (104) that can transmit a carrier signal (107) having a modulation signal imposed thereon, wherein both the carrier and the modulation signal are derived from the same reference. Monitoring stations (108) receive transmissions from two or more remote sites, and determine the differential, if any, between the frequencies of the recovered modulation signal. The system then acts upon this information to provide correction information to one or more of the remote sites as necessary to ensure substantial carrier frequency similarity between the remote sites.

Abstract: In a communication system having a plurality of base stations for communication with mobile terminals, each station is allocated one of nine communication channels. The allocation is arranged such that adjacent channels are spaced further apart than non-adjacent channels so as to eliminate interference.

Abstract: A direct conversion FM receiver that comprises a quadrature mixer, an A to D converter, a digital demodulator, a digital phase lock loop, and frequency offset setting means is disclosed. The quadrature mixer receives FM signals and mixes them with a local oscillator signal to produce an analog in-phase baseband signal and an analog quadrature baseband signal. The analog in-phase baseband signal and the analog quadrature baseband signal are converted into digital signals by the A to D converter. The digitally converted baseband and quadrature signals are digitally demodulated and filtered by the digital demodulator such that modulation information is produced. The modulation information is used, at least in part, to control the phase lock loop means.

Abstract: A clock-driven pulse source is used to apply repetitive short pulses to the squelch control connection point of the squelch circuitry of a radio receiver to deactivate momentarily the squelch circuitry at regular intervals. This provides periodic noise bursts of "de-squelch" pulses on an otherwise silent radio in order to inform the radio operator that the radio is live and that the volume is adequate. A light may also be connected to the system to provide a second, visual, indicator of the operational status of the radio. This radio receiver operational checking system may also be utilized where there are two or more radios in use by providing an additional clock-driven pulse source for each radio in use. The system may be arranged so that the status of individual radios may be quickly ascertained by sound and/or by light indicators.

Abstract: A carrier is received containing a plurality of signals within a first frequency band, for example television signals within the cable television band. The signals are upconverted to a second frequency band above the first band wherein a selected one of the upconverted signals will reside at an intermediate frequency within the second band. The selected upconverted signal is input to a homodyne detector operating at or near intermediate frequency. In-phase and quadrature signals output from the homodyne detector are digitally processed to recover a baseband signal.

Abstract: In the case of a method for the generation of an amplitude-modulated ISB transmission signal from different AF signal (NF1,2), the signal vectors are split into signal components (x1,y1 and x2,y2, respectively), components sums (X,Y) are formed from the signal components and an amplitude signal (A(t)) and a harmonic phase signal are derived from the component sums. Amplitude signal and phase signal are then further processed separately and combined at the single transmitting tube (43) by combined amplitude modulation and phase modulation into the final transmission signal.

Abstract: Disclosed is a mobile radio-receiver system built-into an FM radio-receiver set installed in a vehicle, wherein a reproduction characteristic of a reception signal, such as a sound signal, having noise superimposed thereon is improved. The mobile radio-receiver system includes a space diversity unit which receives two reception signals and selects one reception signal on which noise is smaller than on the other reception signal, and a signal prediction unit which ignores the selected signal for a predetermined time in which large noise remains in the selected signal, and predicts a reception signal for the ignored selected signal for the predetermined time, so that a quality of a reproduction sound from the FM radio-receiver set is greatly improved.

Abstract: To increase the fidelity of radio reception in a moving receiver, for example a car radio, the signals received from various antennas on the radio are mixed with a carrier in the receiver, and the resulting mixed signals, directly and 90.degree. phase-shifted, are added to a summing signal, in which, additionally, the phase positions of the direct and 90.degree. phase-shifted signals are changed in dependence on the phase difference between the respective intermediate frequency mixed signal and the overall summed signal in a direction to maximize the summed signal (u.sub.s).