Abstract: An FM stereo receiver includes a level detecting circuit for detecting the received electric field intensity and a pseudo stereo circuit for changing the phase of an entered signal and outputting two signals different in phase. When the level detecting circuit detects a received electric field intensity below a threshold level, monaural signals produced from outputs of a stereo demodulator are applied to the pseudo stereo circuit to produce pseudo stereo signals.

Abstract: A decoder for use in an FM stereo broadcasting system in which the usual difference signal S and a compressed version S' of the difference signal are transmitted, automatically selects on a continuous basis for de-matrixing with the received sum signal M either an attenuated signal S' or the usual difference signal S based on the protocol that the attenuated signal S' is always selected unless the usual difference signal S is higher in level than a predetermined threshold potential related to the signal level at the knee of the expansion characteristic. The decoder eliminates the need for the relatively expensive analog variable gain amplifier used in prior art decoders and is less sensitive to time constant errors and errors due to multipath distortions.

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 circuit is provided for detecting the level of noises in received FM signals in an AM/FM receiver which includes at least an FM intermediate-frequency amplifier, an FM detector connected thereto, an AM intermediate-frequency amplifier and an AM detector connected thereto. This FM noise level detecting circuit includes a frequency converter receiving the output of the FM detector for converting noise components contained in the output of the FM detector into a noise signal of the AM intermediate-frequency, which is in turn outputted to the AM intermediate-frequency amplifier, so that the converted noise signal is amplified by the AM intermediate-frequency amplifier and then detected by the AM detector to produce a DC signal. The signal thus obtained is not only representative of the level of the noise contained in the received FM signal, but also representative of the received FM signal strength.

Abstract: A blend control circuit for attenuating the L-R signal in a stereo system as a function of a d-c control potential. The circuit is designed to operate with a very low supply voltage and to provide a nearly linear control of stereo separation as a function of control potential.

Abstract: An FM stereo signal demodulator for separating a composite stereo signal into left and right signals is disclosed wherein the amplitude of the 38 kHz signal necessary to separate the composite signal is varied in accordance with the field strength of a received signal.

Abstract: Receiver comprising a field-strength detector for measuring the received signal amplitude and a noise reduction circuit connected thereto via a control signal generating device for reducing audio-frequency noise in the output signal of the receiver, which control signal generating device has an attack and a recovery time constant at a decrease and an increase, respectively, of the received signal amplitude measured by the field strength detector, the recovery time constant being greater than the attack time constant. By adequate control of the cross-talk attenuation of a stereo signal and of the audio band-width, sudden variations in the sound quality at rapid and large field strength variations are prevented. To this end the control must be continuous and must, in the event of field strength variations follow the decrease of the field strength more rapidly than the increase.