Abstract: In a circuit for decoding a multiplex signal in a stereo receiver, where the multiplex signal contains a composite signal (L+R) in the base band, a subcarrier modulated with a difference signal (L-R), and a pilot signal with half the frequency of the subcarrier, the multiplex signal in digital form is multiplied (2, 3) by a reference carrier generated with a sampling clock signal (14) produced in the radio receiver, where the reference carrier is present in two phase positions shifted 90.degree. with respect to each other. The mix or product signals resulting from this multiplication are multiplied (4, 5) by one correction signal each, thus forming corrected mix signals. The corrected mix signals are added (6) and supplied to a matrix circuit (8, 9), together with the composite signal, to create respective stereo audio channel signals (L, R).

Abstract: Digital tuning of a locally generated frequency supplied to a frequency converting mixer, a mobile radio receiver is provided with great economy of components by utilizing the sampling rate oscillator for an analog-to-digital converter provided at the output of an analog intermediate frequency amplifier of the receiver as the source of the difference frequency for a phase locked loop (PLL) for control of the phase of a local oscillator for the mixer or mixers. All frequencies used to supply local oscillations to mixers, as well as the operating frequency of the phase locked loop are integer number multiples of the sampling rate pulse generator. Some division stages have fixed dividers and others have divisors selectable by a tuning processor and in some of the divisor connections it is useful to interpose a fixed or selectable-factor multiplier. A sampling rate of 42.75 MHz is recommended and an intermediate frequency amplifier frequency which is a rational number multiple of 57 kHZ, preferably 10.

Abstract: A new digital oscillator is described that can be synchronized with a broadcast digital input signal by iteratively rotating the phase of the complex oscillator signal by increasing or decreasing the components, depending upon the phase difference between the broadcast signal and the oscillator output signal.

Abstract: A mobile radio receiver, for example, a car radio, needs a circuit to detect and suppress adjacent-channel interference. This can be done by using bandpass filters (14) of differing bandwidth. The present invention dynamically adjusts bandwidth to an optimum value by continuously comparing (13) a first signal level, upstream of the bandpass filter, to a second signal level, downstream of the bandpass filter, to derive a difference value representative of adjacent-channel interference, then uses an electronically controlled selector switch (6) to select a particular filter (14.sub.N) whose bandwidth is sufficiently narrow to cut out the interfering broadcast signal. A table associating each magnitude range of interference with a particular filter bandwidth assures that bandwidth is broadened as interference diminishes, thereby assuring sufficient reception signal strength.

Abstract: Sample values of a digital signal of a first sample rate are supplied to a digital filter for conversion into a digital signal of a second sample rate. The coefficients of the digital filter are calculated by a processor from the ratio of the sample rates or are obtained by a read-only memory containing sets of coefficients for respective sample rate ratios for which the apparatus is usable. Filtered sample values are read out of the digital filter at the desired second sample rate. A buffer memory is used at the input of the digital filter and a regulator is provided to prevent fluctuations in the filling of the buffer memory from emptying or exceeding the capacity of the buffer memory.