Abstract: A multi-band scanning radio receiver operable without reprogramming in a plurality of geographical regions. Digital codes for public-service-band frequency allocations for each of a plurality of geographical regions are stored in a memory which is sequentially accessed to read the digital codes for the frequency allocations for a selected geographical region. A frequency synthesizer loaded with a digital code read from memory performs band switching and supplies tracking signals and a local oscillator signal to multi-band RF amplifier and mixer circuitry.

Abstract: To suppress tuning noise interferences, and particularly transients, such as whistles and the like, especially in FM receivers during returning of the receiver, an inter-station retuning muting circuit is, in accordance with the invention, modified by including therein a switchable filter (2) having a low-frequency cut-off (f.sub.g2) which is higher than the frequency of noise interference due to retuning of the receiver, the filter being switched to the higher frequency cut-off level for a period of time (T.sub.E) which exceeds the normal muting time (T.sub.E) of FM receivers.

Abstract: A receiver includes a receiving circuit for receiving an electromagnetic carrier wave modulated by a message signal, a detector ciruit for separating the message signal from the carrier wave, and an output circuit. The detector circuit has a Q ratio sufficiently low that the detectable band width is more than twice the modulation frequency change. The detector output signal has a noise voltage level when no carrier is present that is higher than the voltage of the message signal with a carrier present. An output circuit senses the level of the detector output signal and passes signals with a voltage level below a predetermined level and otherwise blocks the output signal. The filtering of the output circuit is sufficiently low that its response time is faster than a tenth of a second. The output circuit includes a noisy input related to the detector output and a reference input.

Abstract: A circuit arrangement comprises a controller (20) for producing a control signal selectively indicative of normal and diagnosis modes. Responsive to the control signal, an IF stage (12) processes desired RF and diagnosis input signals into an IF signal of an IF level. Responsive to the IF signal and a reference signal of a reference level squelch signal producing circuit (15) produces a squelch signal when the IF level is lower than the reference level. First and second signal generators (26, 27) generate first and second threshold signals of first and second threshold levels, respectively. The second threshold level is lower than the first threshold level. Responsive to the control signal, a switch circuit (22) selects the first and the second threshold signals as a selected threshold signal. A line (29) supplies the selected threshold signal to the squelch signal producing circuit as the reference signal.

Abstract: Noise detector for detecting noise pulses in a non-limited radio broadcast signal modulated on a carrier, comprising an amplitude detection circuit and coupled thereto a first signal comparison circuit having a signal input and a threshold input, a first threshold signal depending on the average input level of the noise detector and a second threshold signal depending on the noise pulse repetition frequency being applied to this threshold input. To limit the repetition frequency of the detection output signals of the noise detector without reducing the input sensitivity, the threshold level of the noise detector is controlled in forward direction in dependence on the field strength and the noise pulse repetition frequency.

Abstract: Noise detector for selecting noise pulses from a non-limited FM radio broadcast signal modulated on a carrier, comprising an amplitude detection circuit and a signal comparison circuit. This signal comparison circuit produces a detection signal when its input signal exceeds a threshold level which varies with the average input level of the noise detection, for example, the average field strength. A noise selection being adapted to the human ear and based on the ratio between the noise pulse amplitude and the average input level is realized by means of a logarithmic level detection circuit. The logarithmic conversion therein renders a simple setting of the value of ratio possible, and provides a dynamic compression.

Abstract: A communication system for providing reliable transfer of digital data in such system as a security system between source of data 214 and user 213, and between user 213 and end use of data 215. When the false alarm rate requirement of the security system is specified in less than one in ten years, this tight requirement must also apply to the communication link even though the RF transmission path might use the very noisy 60 Hz power line. Digital data signals are transmitted only when a detection is made at source of data 214 or when user 213 outputs an action command to end of use data 215. Thus the communication system must maintain the low false alarm rate under two conditions: (1) where no data signal but noise and interference is received over long periods of time, and (2) where a data signal pulse noise is received.

Abstract: A television receiver has provisions for a second audio program (SAP) and an indication for signifying when the SAP is present and a muting circuit for muting the SAP, both in response to the output signal of a SAP detector. A filter capacitor is coupled to the detector output to prevent flicker of the indicator due to noise. To prevent the filter capacitor from incorrectly maintaining an indication of the presence of a SAP, thereby preventing proper SAP muting, when a new channel is selected, channel change signal causes a semiconductor switch to discharge the filter capacitor. A SAP defeat switch coupled to the SAP provided the SAP detector output is to defeat the SAP when stereo is being received. To prevent the filter capacitor from discharging to rapidly and thereby creating an audible transient when either the defeat switch or channel change switch is operated, a resistor is coupled between the SAP detector output and the common junction of the SAP defeat and channel change switches.

Abstract: A television receiver has provisions for a second audio program (SAP) and an indication for signifying when the SAP is present and a muting circuit for muting the SAP, both in response to the output signal of a SAP detector. A filter capacitor is coupled to the detector output to prevent flicker of the indicator due to noise. To prevent the filter capacitor from incorrectly maintaining an indication of the presence of a SAP, thereby preventing proper SAP muting, when a new channel is selected, channel change signal causes a semiconductor switch to discharge the filter capacitor.

Abstract: A squelch circuit in which a phase locked loop (PLL) (5) having a voltage controlled oscillator (VCO) (7) and a phase comparator (10) is used to detect the number of zero crossings, these being low for a speech signal and high for noise. The error voltage produced in the phase locked loop (5) is fed through a network (12) which ensures that the matching of the input signal to the oscillator is faster when the input frequency drops than when the input frequency rises. The input signal is clipped to enhance the frequency spectra of speech by using a limiting amplifier. The muting gate (2) output is derived from the VCO (7) control voltage of the PLL (5) to mute the output of the receiver when the VCO (7) output frequency is higher than a pre-set frequency for more than a pre-set time.

Abstract: A radio receiver has an IF amplifier whose output is connected to an AM demodulator and an FM demodulator. The noise level at the output of the FM demodulator is measured and, when it exceeds a predetermined threshold level, the audio output stage of the receiver is disconnected from the circuit. Noise generated when amplitude modulated signals with a high degree of modulation are received may cause unwanted disconnection of the output circuit. This is prevented by a circuit connected to the output of the AM demodulator which detects negative peaks of the modulation signal which exceed a negative threshold. The integrated peak signals form a correction signal which prevents disconnection of the output stage.

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: A single sideband communications system conveying a message through a transmitter to one or more predetermined receivers which are enabled by a coded squelch signal unique to the predetermined receivers is disclosed. The transmitter comprises means to angle modulate both the pilot signal and the information bearing single sideband signal with the coded signal at a predetermined deviation and to transmit the resulting signal.Each receiver frequency control means tracks the frequency excursions of a selected portion of the transmitted signal up to predetermined limits so that the message can be demodulated without frequency distortion being introduced. Each receiver demodulates the coded squelch without interfering with the message demodulation or tracking functions and activates the receiver squelch of those preselected receivers.

Abstract: Radio-receiver having a frequency-locked loop which comprises, arranged one after the other, a tunable voltage-controlled oscillator, a mixer stage, a filtering element, as well as a frequency-voltage converter which is connected to the tunable voltage-controlled oscillator, several stable tunings being possible for each transmitter. An unambiguous selection is made from these stable tunings of a tuning to a desired station by muting the radio receiver in the other stable tuning frequency ranges. To this end the radio receiver according to the invention comprises a muting circuit as well as a control circuit for the muting circuit in which use is made of a further frequency voltage converter comprising an all-pass frequency-dependent 180.degree. phase shifting network, a phase detector and a limiter.

Abstract: A muting circuit for an AM stereophonic receiver of the type that having a detector circuit operating upon an AM stereophonic signal, the carrier of which is phase-modulated by the difference signal of first and second stereo channel signals, for detecting the difference signal. The muting circuit includes a muting signal generating circuit for detecting the output level of the detector circuit exceeding a predetermined value and for generating a muting signal at least for periods when the predetermined value is exceeded, and a muting switch circuit for attenuating the output of the detector in response to the muting signal.

Abstract: A noise removing apparatus in an FM receiver includes a high-pass filter (29) receiving an output from an FM detector circuit (11), a gate (15) being interrupted in response to a pulsive noise detected by level-discriminating an output from a variable gain amplifier (35) receiving an output from the high-pass filter (29). Transistors are provided for controlling the gain of the variable gain amplifier (35) according to the magnitude of a terminal voltage of a capacitor which is charged according to an output from a rectifying circuit (43). The noise removing apparatus further includes a voltage generator (51) for generating a voltage proportional to a received electric field strength and a circuit (53) for varying an amount to be charged in the capacitor according to the magnitude of a voltage from the voltage generator (51) for maintaining the gain of the variable gain amplifier (35) large at the time of strong electric field, so that a multipath noise can be effectively removed.

Abstract: A selection circuit for series connection between the output of the detector stage and the input of the audio amplifier. The selection circuit requires a minimum number of components and is useful to drive a tuning indicator or similar type circuit.

Abstract: This invention relates to a FM receiver and more particularly to a FM receiver having an auto-scanning circuit. In a conventional FM receiver using an auto-scanning circuit, a window comparator is provided at the latter position of a demodulation circuit. When an electromagnetic wave is received, scanning is stopped by using the both of DC component of demodulation voltage generated within a specific range of frequencies around the tuning frequency and a squelch signal. In the present invention, in order to utilize stabilized parts of DC component of the demodulation voltage, as much as possible, except for the rising parts of the DC component, a timing circuit is provided which is switched on by the demodulated signal outputted from the window comparator continuing for a given time, thereby a perfect tuning is assured.

Abstract: Disclosed is a muting circuit, in which the generation of click noise is prevented in that the muting operation is caused to occur at an instant when the instantaneous level (i.e., waveform level) of the input audio signal becomes zero for the first time since the appearance of a muting signal.

Abstract: A receiver for AM signals, in which the carrier is amplitude modulated with a first signal (L+R) and phase modulated with a second signal (L-R), includes a circuit for reducing distortion in the output signal due to amplitude overmodulation. This circuit includes an overmodulation detector for controlling a switch in a phase demodulation signal channel, which switch, coupled between a demodulator and an integrator in this signal channel, effectively short-circuits the input to the integrator causing the output thereof to remain constant for the duration of the overmodulation.

Abstract: A noise detector and data signal receiver for a frequency modulation system has a first phaselock loop circuit (300), responsive to the received signal, for providing a signal indicative of the noise level and a first stage of demodulation of the received signal. A high speed comparator (330) of the first phaselock loop circuit provides a 90 degree phase-shifted signal which exhibits lesser delay and is substantially in phase with the input. Accordingly, the noise detection capability of the phaselock loop circuit (300) is improved. A second phaselock loop (200), also responsive to the received signal, extracts a voice signal from the received signal. A third phaselock loop (400) responsive to the once demodulated output signal of the first phaselock loop (300), extracts a digital data signal from the received signal. Squelch circuits (120, 121), activated at separate particular levels of noise, are responsive to the noise level indicator signal of the first phaselock loop.

Abstract: A receiving reproducing system for an automotive radio detects the surrounding noise level other than the output sound thereof, in the sound field extending in the passenger compartment of an automobile, and the level which is dependent upon the received signal level of an antenna. The receiving reproducing system partly controls its output sound volume proportionally in accordance with the surrounding noise level and partly lowers its output sound volume in dependence upon the reduction in the received signal level. Even under the circumstances where the surrounding noise level is high and where the received signal level is low, the sound volume of the output sound containing many noises can be prevented from being raised.

Abstract: In a receiver of the type capable of receiving a second or third subchannel audio signal which contains no pilot signal and which is multiplexed with the television audio signal, only the subchannel signal frequency components pass through a band-pass filter the output of which is fed to a clipper circuit so that the carrier level of the output is suppressed. The output of the clipper circuit is detected whether the subchannel signal is present or absent or subchannel signal is increased so that a squelch circuit is turned off and a display device is turned on or vice versa.

Abstract: A circuit is described for maintaining an input signal to a limiter used to limit amplitude excursions of a signal to be angle demodulated. Means are provided for detecting a temporary loss in signal to said limiter resulting from the loss of signal due to large negative amplitude modulation or other factors. When the amplitude of the angle modulated wave falls below a predetermined minimum, a substitute intermediate frequency signal is generated to maintain the limiter in a limiting condition during the temporary loss in broadcast signal. The substitute intermediate frequency signal has a frequency substantially equivalent to the intermediate frequency signal developed from the broadcast signal during periods when the amplitude of the broadcast signal is adequate. The substitute signal prevents the occurrence of noise generated from an angle demodulator due to a temporary loss in signal.

Abstract: A radio receiver comprises a phase locked loop and an automatic frequency control loop which are selectively coupled with a voltage-controlled local oscillator to control a local oscillator frequency. The phase locked loop and the automatic frequency control loop have a common loop filter which supplies the voltage-controlled oscillator with a control voltage. The loop filter is arranged so that its time constant may be switched from a small value to a great value in response to switching of the operation mode of the voltage-controlled oscillator from a phase locked loop control mode for the selection of broadcasting station to an automatic frequency control loop control mode for the maintenance of the local oscillator frequency after tuning of the radio receiver. The radio receiver can be arranged so that the local oscillator frequency may be maintained by the phase locked loop after the tuning of the receiver to a weak broadcast signal when muting control is rendered ineffective by a muting switch.

Abstract: A high frequency squelch circuit for communications receivers with relatively long time delay when operating on weak signals with a short time delay on strong signals which completely eliminates any audible noise burst, and with continuously variable delay as an inverse function of signal strength at intermediate signal levels. The high speed squelch performance is achieved without degrading chatter performance by operating at frequencies above the audio range and utilizing wider noise bandwidth.

Abstract: A superheterodyne receiver is described for demodulating signals containing both amplitude and angle modulation components. An intermediate frequency signal is produced which is simultaneously amplitude detected as well as angle demodulated. Detector means are provided for detecting the occurrence of high negative amplitude modulation peaks of the broadcast signal. During high negative amplitude modulation peaks, the angle demodulator output is held at a fixed level until the amplitude of an input signal is restored to a predetermined minimum level.

Abstract: A noise removing apparatus is interposed between an FM detecting circuit and a stereo demodulating circuit. The noise removing apparatus is responsive to a pulsive noise included in the output from the detecting circuit to enable a first gate to interrupt transmission of the output. Although the stereo pilot signal is disturbed during the interruption period, the disturbed stereo pilot signal is canceled by a pseudo-stereo pilot signal (a signal similar to the pilot signal) separately generated, whereby the disturbed stereo pilot signal is prevented from being applied to the stereo demodulating circuit.

Abstract: A system for automatically adjusting the threshold sensitivity of an FM receiver (muting) to prevent noise capture and reduce the effects of distortion due to multipath reception. A crystal controlled oscillator drives a suppressed carrier modulator which in turn delivers sideband signals at F/88 and -F/88, where F is the IF center frequency of 10.7 MH.sub.z. The sidebands are injected into the FM receiver between the IF amplifier output and the input of a quadrature detector (discriminator) and fall outside of the maximum .+-. excursion of FM modulation within the IF bandpass, but are separated from F by less than the adjacent channel spacing. Proper adjustment of the level of these sidebands prevents noise capture and reduces FM Multipath Distortion.

Abstract: In the circuit according to the invention the entire FM-demodulator output signal is evaluated, that is to say the sum of the low-frequency signal and the d.c. voltage (AFC) component. The absolute value is produced therefrom and an attenuator circuit becomes operative in the low-frequency channel when the absolute value of the demodulator output signal exceeds a predetermined threshold value. This not only enables the suppression of spurious receptions, but also the suppression of intermediate receptions (the reception of two transmitters on the filter edges) and surging of noise. The circuit can be easily implemented in integrated circuit technique.

Abstract: A system is provided for developing a gating signal when a radio-frequency signal receiver is tuned to the center-frequency of a selected radio-frequency signal. The system comprises circuit means for tuning the receiver to a plurality of frequencies within a range of frequencies which includes the selected signal and for producing an intermediate frequency signal corresponding to the frequency to which the receiver is tuned. A frequency discriminator is coupled to the circuit means and is tuned to a predetermined frequency, with the frequency discriminator being responsive to the intermediate frequency signal for developing an output signal having a DC component which varies systematically in accordance with the deviation of the intermediate frequency signal from said predetermined frequency.

Abstract: In a muting arrangement of a radio receiver using a phase-locked loop frequency synthesizer as a local osicillator, a detector detects an in-lock or out-of-lock state of the phase-locked loop through an output state of a phase comparator included in a feedback loop of the phase-locked loop frequency synthesizer, and a mute gate provided in a signal transmission path of the receiver is operated to mute an audio output when the phase-locked loop is out of lock. An indicator may be provided for visually indicating that the phase-locked loop is in lock.

Abstract: A hands-free telephone system is disclosed utilizing an infrared transmitter and receiver to permit wireless speech transmission. The transmitter uses frequency modulation imposed on the infrared signal and includes carrier shift signaling arrangements for indicating a low battery condition and transmitter turn-off. The receiver utilizes a noise detection circuit for permitting remote turn-on, for squelching noise in the voice path, and for feeding an alerting signal to a loudspeaker to indicate that the received signal is excessively noisy. The portable transmitter must then be moved or redirected to provide a better line-of-sight signaling path.

Abstract: Two semiconductor diodes are serially interconnected across a ratio detector in the same polarity. When the detected output from the ratio detector reaches a predetermined magnitude, both diodes are conducting and the detected output is taken from the junction of the diodes. When the detected output from the ratio detector falls due to a lower received signal level, an increase in noise level is ordinarily experienced. Because the output of the ratio detector is lower, the diodes are no longer fully conductive. This causes an increase in output impedance and a corresponding reduction in noise output.

Abstract: A signal processing circuit for an FM signal receiver suitable for constructing in an integrated circuit is disclosed. The signal processing circuit comprises a differential amplifier circuit receiving first and second demodulated signals of the frequency modulated signal and providing first and second output signals. A current switching circuit has a first input point for receiving the second output signal of the amplifier and a second input point for receiving the output of a constant current source. The current switching circuit switches current paths from the first and second input points to first and second output points in response switching control inputs. A first current mirror has an input point coupled to the second output point of the current switching circuit and an output point coupled to the first output signal of the amplifier circuit.

Abstract: A balanced, doubly tuned gate couples between the mixer and intermediate frequency (IF) stages of a conventional radio receiver. The network is comprised of a pair of matched transformers interconnected in a balanced configuration, with the first transformer tuned to the mixer and the remaining transformer tuned to the IF stage. Capacitors interconnect the two transformers resulting in a Butterworth filter network.Two diode pairs connect in shunt across selected windings of the transformers. Direct current bias normally biases the diodes to a nonconducting state, thereby allowing the mixer signals to pass to the IF stage. A blanking signal from the receiver blanker drives the diodes to conduction thereby decoupling the mixer from the IF and blanking the receiver.Due to the doubly balanced nature of the gate, blanking is accomplished with a minimum of switching time. Moreover, the shunt diode switching scheme provides superior attenuation in the blanking mode and enhanced operation in the normal mode.

Abstract: A muting range setting circuit for an FM receiver uses a pair of differential amplifiers. Each of the differential amplifiers employs the same transistors having like polarity with common input and output terminals. The output of the tuner AFC is compared with an input reference voltage in the differential amplifier circuit and the output representing the frequency deviation of the FM detecting circuit is applied to the gate driving circuit for control of the muting operation.

Abstract: Disclosed is a muting circuit, in which the generation of click noise is prevented in that the muting operation is caused to occur at an instant when the instantaneous level (i.e., waveform level) of the input audio signal becomes zero for the first time since the appearance of a muting signal. .Iadd.A muting-off circuit is also disclosed for turning off the muting circuit. .Iaddend.