Abstract: An FM stereo radio data-system receiver has a front end including an FM discriminator that produces a composite signal composed of an AM stereo signal, including a 19 KHz pilot, and an AM digital-data signal. A dual-bandwidth phase locked loop (PLL) locks onto the pilot and serves both, as the decoder of the stereo portion of the composite signal, and as a generator of a strong stable 38 KHz carrier for use in regenerating the bit rate clock signal and for decoding the data-symbol signal of the digital-data portion of the composite signal. Advantages include economy of circuitry, a simpler and less costly high pass filter, and greater reliability in the decoding of the data signal.

Abstract: A stereo decoder for use in a stereo FM radio receiver includes a phase-locked loop; for detecting the 19 KHz pilot signal in the FM composite signal; for generating the 38 KHz subcarrier for use as a reference signal to a double balanced gating circuit that combines he L-R and L+R components of the stereo composite signal to produce the left audio and right audio signals separately; and for providing a 19 KHz reference signal for use in the pilot detector and pilot indicator circuit. The phase-locked loop includes a mixer to which a 19 KHz reference and the composite signals are applied, a low pass filter switchable from a first bandpass of about 300 Hz to a second bandpass of about 10 Hz connected to the output of the mixer a voltage controlled oscillator connected to the output of the filter that has a natural operating frequency of 38 KHz and a divide-by-two circuit connecting the oscillator to an input of the mixer.

Abstract: An FM stereo decoding and separating circuit has an (AM) demodulator multiplier to which is connected the FM stereo composite signal and a signal of dominant frequency equal to and in phase (0.degree.) with respect to the pilot signal for retrieving the L-R signal from the composite signal. This demodulator also has a blend control circuit for diminishing the magnitude of the L-R signal as a function of a blend control voltage that may be applied to the input of the blend control circuit. The decoding circuit also includes a special multiplier to which is connected the FM stereo composite signal and a signal of dominant frequency equal to that of the 38 KHz subcarrier but shifted 90.degree.

Abstract: A stereo FM radio transmission system with FMX transmission and reception capability includes a transmitter that transmits a pilot-coherent FMX-tone indicator signal at a frequency of an exact integer submultiple of the pilot frequency. The system also includes a receiver for dividing the frequency of the received pilot signal by various submultiples, nearly equal to the exact submultiple, toward quickly finding a match in phase of the received tone and the received pilot and finally dividing the pilot by the exact submultiple to establish an operational lock mode of the receiver tone detector to keep-on an FMX-indicator lamp, to change the receiver decoder to an FMX-reception operating mode and to stand by to quickly recapture the pilot and FMX-tone in the event of multipath or other interfering signals.

Abstract: To a standard AM radio receiver there is connected an impulse-noise suppression system comprising a preliminary blanking gate adapted for connecting to and for interrupting the AM-modulated signal path at the input of the IF section, and an audio blanking gate adapted for interrupting the audio circuit. Both blanking circuits detect impulse noise at the RF amplifier and with appropriate delays blank both points. Audio blanking masks the audio disturbance caused by the blanking in the AM-modulated-signal path. Audio blanking time is preferably from 2 to 3 times the duration of the blanking of the AM-modulated-signal path and is thus kept very short causing a minimum interruption of the wanted audio signal. Associated with the audio-signal-path blanking circuit is a sample and hold circuit for smoothing the blanked audio signal and virtually eliminating an audio disturbance or noise that is otherwise generated by the audio blanking circuit itself.

Abstract: In an integrated AM-FM radio circuit connected for operation in the FM mode, the voltage appearing across the normally unused AM tank at the IF amplifier is noise in that AM band centered at 455 KHz. That noise, which is present only when the IF amplifier is not limiting due to the presence of an FM signal therein, is used for muting the receiver. The noise is passed through a simple IC-on-board low pass filter to a noise detector and then to a voltage controlled attenuator to attenuate the demodulated audio from the FM detector to the audio amplifier.

Abstract: An integrated circuit AM radio receiver includes a scan-tuner comprised of a frequency synthesizer with micro-processor controller. The tuner stops scanning when an AGC derived signal increases beyond a predetermined level indicating a strong station and additionally when another signal falls below a predetermined level indicating that the radio is accurately tuned to the station frequency. The another signal is derived from an FM discriminator simultaneously using the same coil as is employed for tuning the last AM-IF stage.

Abstract: A radio receiver has one or more automatic gain control (AGC) circuits that each generate the gain-determining bias current in a separate main channel section or sections, e.g. RF amplifier, mixer, IF amplifier, of the radio receiver. The receiver is for the most part formed in an integrated silicon circuit, wherein the gain-controlling current in each case biases the base-emitter junction of an amplifying grounded-emitter transistor so that the gain thereof is directly proportional to the magnitude of the AGC control current. That current in each case is caused to flow through a diode string to generate a voltage drop thereacross that is logarithmic function of the AGC control current as well as of the radio signal amplitude at the input of the AGC controlled section. The sum of those diode voltages may be taken to produce a log of the product of the gains of the AGC controlled sections. Thus a sum signal is a logarithmic function of the radio signal input to the receiver.