Abstract: A wireless communications receiver having an adaptive squelch system and operable in multiple states including a receiver (11) that provides a received signal when operating in a clear (unscrambled) state and when operating in a secure (scrambled) state; a squelch function (13) that generates an unsquelch signal when the received signal satisfies a quality level; and a controller (15) that sets the quality level to a predetermined level that corresponds to the receiver operating state.

Abstract: An apparatus and method for discriminating and suppressing noise within an incoming signal which provide a first signal processing unit for processing the incoming signal to generate a first iteration signal representing average difference signal level of the incoming signal; a second signal processing unit for processing the first iteration signal to generate a second iteration signal representing specified aspects of the first iteration signal; a prediction unit for generating a predicted value for the second iteration signal from earlier samples of the second iteration signal; a logic unit for determining a threshold difference between the second iteration signal and the predicted value, the logic unit generating a logic output having a first value when the threshold difference exceeds a predetermined threshold value and having a second value when the threshold difference does not exceed the predetermined threshold value; and a muting unit for muting signals which is operatively connected to receive the in

Abstract: A communication device (100) having a receiver (106) and an audio output device (116) is provided. The communication device (100) includes a digital signal processor DSP (110) for measuring the level of signal energy in a first segment of the frequency spectrum of the received signal to dynamically establish a squelch threshold. The DSP (110) is also used to measure the level of signal energy in a second segment of the frequency spectrum of the received signal. The communication device (100) also includes audio gates (114). The audio gates (114) provides for the unmuting of the audio output device (116) when the signal energy contained in the second segment of the frequency spectrum of the received signal is below the squelch threshold.

Abstract: A clock-driven pulse source is used to apply repetitive short pulses to the squelch control point of the squelch circuitry of a radio receiver to deactivate momentarily the squelch circuitry at regular intervals (FIGS. 2B, and 2D). The repetitive short pulses being applied to the active squelch circuitry of a radio receiver to deactivate it momentarily at regular intervals may, according to the present invention, be applied directly or through reactive coupling to the antenna associated with the radio receiver (FIGS. 2M and 2N). 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.

Abstract: An essentially zero intermediate frequency receiver (100) for recovering an information signal from a received signal (110), which includes means for blanking noise signals which may otherwise deteriorate performance, comprises a receiver (10) for recovering the information signal and a noise blanker (28). The receiver (28) comprises at least one conversion mixer (32B) for operating on the received signal (110) to provide an essentially baseband signal (125B), at least one delay filter (40B) coupled to the conversion mixer (32B) for producing a delayed essentially baseband signal, and at least one blanker switch (S1-S4) for operating on the delayed essentially baseband signal to temporarily prevent recovery of the information signal in response to a control signal (58). To provide the control signal (58), the noise blanker (28) is coupled to the receiver (10) for operating on either the essentially baseband signal (125B) or the received signal (110) as a noise blanker input signal.

Abstract: The period of time that the squelch circuit maintains a radio receiver's audio amplifier active after the signal strength of a received carrier fades below a threshold level is inversely proportional to the strength of the received carrier immediately before the fade. This threshold level is also variable. If, immediately before the fade, the received signal strength exceeds a predetermined trigger level (Vtrg) the threshold level is raised. A buffer amplifier (102) charges a capacitor (C) to a voltage which is proportional to the strength of a received carrier. If the carrier fades below a threshold (Vth2 or Vth3, the buffer is disabled and the capacitor slowly discharges through a resistor (R). When the voltage at the capacitor crosses a reference voltage (Vref1) the output of a comparator (104) switches, thereby deactivating the receiver's audio amplifier.

Abstract: A muting control circuit is provided in which muting is performed when any one of a plurality of unlock detection signals is detected, indicating circuits is unlocked or when a data error is detected in a demodulator. In this way, reading time can be shortened to the minimum time required for muting. In addition, when one unlock detection circuit is triggered due to a disorder in the input, the unlock detection signal is provided immediately, so that the muting control signal is supplied and muting can be performed even when there is a time delay before the unlock detection circuit detects an unlocked state.

Abstract: For elimination of pulse type interference in an FM receiver by intermittent blanking of the received signal while interfering pulses are present and substitution of a synthetic signal during the blanking intervals, the synthetic signal substituted during the blanking intervals is produced by interpolation using finite duration impulse response digital filters, instead of using the last undisturbed value of the received signal modified by integration of its last value of rate of change with respect to time. The determination of the blanking interval is optimized by reference to the maximum and minimum peak values of the output of an AM detector of the received signal and comparing an interference signal magnitude thus obtained with a threshold value of the interference signal, so as to define the blanking interval as the interval during which the interference signal exceeds the reference signal value.

Abstract: A noise reduction system and method for reducing noise occurring during pauses in information bearing audio signals has an audio input connected to one input of a differential output circuit. A variable gain circuit has an input connected to the audio input and an output connected to the other input of the differential circuit. A dc control signal is derived from the incoming signals and controls the variable gain circuit to cause cancellation of a noise only signal during periods of no information bearing audio signals.

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: 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: A noise blanking signal generator for an AM radio receiver includes a product detector adapted to receive an IF signal modulated by an AF signal and synchronously detect the AF signal, a first low pass filter adapted to derive from the product detector a filtered voltage indicating the average IF signal strength, a second low pass filter adapted to derive from the product detector an AF signal voltage and a reference voltage generating circuit ratiometrically related to the product detector through a common DC power supply and effective to generate a reference voltage substantially equal to the filtered voltage in the absence of an IF signal.

Abstract: A method and apparatus for receiving and detecting pulsed RF signals within first frequency band. Incoming pulsed RF signals are supplied to a linear amplifier which amplifies any of the signals within a broader second frequency band. The pulsed RF output signals of the amplifier are supplied to an in-band signal detection circuit controlling switches in the outputs of a first video detector and a frequency discriminator which are also supplied with the amplifier output signals, so that output video and frequency signals are provided only for pulsed RF signals within the first frequency band.

Abstract: Noise blanking is provided by amplifying, limiting and detecting received signals. The detected signals are compared with a threshold circuit. The leading edge of each detected signal that rises at a rate greater than a selected rate to exceed an amplitude threshold level produces a blanking pulse of selected time duration. Low as well as high level noise signals are blanked. Slow rising information signals are not blanked, and fast rising information signals of high level are blanked initially for the selected time duration, but are not blanked thereafter.

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 monitor receiver incorporating a device for reducing the false alarm ratio comprises a frequency changer, a wobbulated oscillator, two band pass filters of which the central frequencies are constant and staggered, two logarithmic amplifiers and two energy detectors, which makes it possible to measure the energy on two staggered frequencies. The logic alarm signal supplied by the comparator is transmitted via a gate inhibited by means for detecting pulsed noises having an energy level greater than a value S', and validated by means of detecting signals of higher energy than a value S". The threshold values S' and S" are calculated by calculator means as a function of the mean value of the energy of the medium and long term persistent noise on frequencies close to the frequency monitored.

Abstract: A squelch circuit for a radio receiver provides for applying the audio signal that has been detected and demodulated to both a low pass channel and high pass channel. The low pass channel passes the audio signal to a low frequency bandpass filter where only the lower frequencies of the demodulated signal are passed. The filtered signal is then average by an averaging detector where the average of the energy contained within the signal is obtained and monitored by a syllabic detector, which upon the occurrence of certain pre-established varying energy levels will indicate the presence of speech in the demodulated signal.

Abstract: An improvement in a radio receiver having a power supply and an audio amplifier circuit comprises a switching circuit interposed between the power supply and the audio amplifier circuit and including a control input responsive to a signal of predetermined level for substantially cutting off the audio amplifier circuit means from said power supply. In accordance with one aspect of the invention, this control input may be coupled to a squelch circuit. In accordance with another aspect of the invention, this control input may also be coupled to an AGC circuit.

Abstract: An automatic threshold squelch circuit, responsive to noise signals from the receiver demodulator, having automatic means for setting the squelch level. A noise detector is coupled to the demodulator and to a comparator and sample and hold circuit such that a predetermined portion of the detected noise signal level is stored in the sample and hold circuit when no signal is being received. The stored noise level is then compared to the detected noise signal from the noise detector and a mute signal is generated in response to the detected noise level exceeding the stored signal level.

Abstract: A receiver with squelch capability includes squelch gate control circuitry which operates the squelch gate on the basis of substantially pure noise even in environments such as offset carrier networks which cause or create substantial interference energy in the receiver.

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: Rapid disconnection of a receiver in response to a small signal-to-noise ratio is provided in that in the receiver there is arranged a FSK demodulator having two channels connected in parallel at the input ends and each having a band-pass filter, an amplifier and a detector whose output is connected to a voltage comparator. The output signal of the voltage comparator is fed to an input of an AND gate in the receiving arm by way of a series arrangement of a high-pass circuit, a demodulator and a low pass filter to the inverting input of a further comparator whose non-inverting input is connected to a comparison voltage by way of a variable voltage divider. The output of the further comparator is connected to the other input of the AND gate.

Abstract: Tape deck adapter apparatus for radio reception, especially for reception of citizen band transmission having widely variable noise levels. The device consists of a receiver which is adaptable for use within a conventional tape deck for energization and operation; the receiver then includes an automatic squelch control circuit of the type which is particularly useful in receiving incoming citizen band transmissions. The automatic squelch control includes reactive means controlling input to the output audio amplifier, such reactance means being controlled by a DC feedback component as derived from the audio output signal, for application to control conduction of the reactance means, and therefore, the amplification of the audio output stage.