Abstract: A squelch circuit (200) having an input is provided including a programmable high pass filter (206) for filtering the input signal to produce a filtered signal. The filtered signal is rectified via a differential rectifier (201) to produce a rectified signal. The squelch circuit (200) also includes a threshold comparator (323) coupled to the differential rectifier (201) for sensing when the rectified signal exceeds a squelch threshold.

Abstract: A noise squelch circuit for a radio receiver (100) includes an adaptive filter (204) for shaping frequency characteristics of a demodulator out put (115) according to factors which effects squelch sensitivity. Such factors may include channel spacing of the receiver, received signal strength level, received signal deviation, and SINAD. The adaptive filter (204) comprises a switched capacitor filter, the response of which may be controlled by a control signal (212) according to one or more of such factors.

Abstract: An improvement in an apparatus which uses a carrier detection threshold level for detecting a carrier signal modulated with binary data. The threshold level is dynamically changed and generally seeks a level above the background noise. The threshold level is maintained constant when the detected signal exceeds the threshold level. An evaluation circuit is able to examine the detected signal to determine whether it contains data or only noise, and if it contains only noise, a possible trapped condition is avoided by raising the threshold level to a level higher than the background noise.

Abstract: A muting circuit for eliminating transient signals generated due to power supply "turn-on" and "turn-off" is presented. In one embodiment, a junction in a signal chain is AC shunted to ground independent of the DC status of the junction. This shunting is in response to a signal generated by a power supply controlling microprocessor when the microprocessor energizes or de-energizes the power supply for a portion of the signal chain coupling signal to the acted upon junction. In another embodiment, the junction is AC coupled to ground during turn-on through a diode in series with a capacitor with the diode first being forward biased and then reverse biased to remove the AC shunt. The biassing of the diode is accomplished by application of two different sources of voltage to respective electrodes of the diode.

Abstract: A noise suppressing circuit has a gate for controlling a composite signal applied to a stereo demodulator of an FM tuner, and a detector for detecting a noise included in the composite signal and for producing a noise dependent signal for controlling the gate to close it. A pilot signal detector is provided for detecting a pilot signal included in the composite signal for producing a pilot dependent pulses. In response to the noise dependent signal and to the pilot dependent pulses, gate control pulses are applied to the gate, thereby closing the gate in synchronism with the pilot signal.

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: A radiotelephone system reduces noise interference during handoff by muting the audio path of a receiver employed in a target base-station (135). After receive a handoff request message, a target base-station (135) mutes the target audio path and determines if the target audio path had been enabled by an undesired interfering signal having a common SAT. If the target audio path had been enabled by a interfering signal having a common SAT, the target base-station (135) will use the SAT and the received signal strength indication (RSSI) of the desired transmission of the subscriber (125) to enable the target audio path. Once the SAT and RSSI are present and adequate, the target audio path is enabled, the source audio path is coupled to the target audio path, and the subscriber (125) is handed off from the source base-station (130) to the target base-station (135) without a third party experiencing an objectionable noise blast.

Abstract: An audio amplifier circuit according to the present invention features an arrangement of a power line with a smoothing capacitor inserted as a power filter and a power line without such a smoothing capacitor. The audio amplifier circuit in which an input stage amplifier of a main amplifier is supplied with power via the former power line has a muting circuit for rapidly charging a negative feedback capacitor for generating negative feedback voltage to be fed back from the following stage of the main amplifier to the input stage amplifier up to a voltage level at which a pop sound is inhibited when the power is supplied and for rapidly discharging the negative feedback capacitor up to a reference operating voltage level when the voltage of the former power line with the smoothing capacitor exceeds a predetermined level, the voltage of the former power line being monitored after the power is supplied from a power supply.

Abstract: A high speed scanning radio has conventional RF amplifier, a mixer, a frequency synthesizer for the generation of local oscillator signals, an IF amplifier, a demodulator, and an audio output stage. The receiver includes a memory for storing a plurality of frequency codes corresponding to respective radio channels and a scan control for reading those codes, two for each channel, into the frequency synthesizer. A linear combination of each pair of distinct frequency codes is utilized to generate a local oscillator signal.

Abstract: In a power line communications apparatus an improvement for blanking or snubbing impulse noise. The impulse noise is detected and used to snub the detected signal. The duration of the snubbing pulses is controlled to assure complete blanking of noise including the trailing noise signals following a main noise pulse which may not otherwise be detectable. Also, the number of snubbing pulses which can occur are limited to prevent too much energy from being snubbed during any given baud period.

Abstract: A FM receiver quickly suppressing defective effect of multipath reflection interference is disclosed. A field strength detecting circuit (8) is responsive to output signals from preceding stage amplifiers (51) in an IF amplifying circuit (5) for detecting the field strength of the received signal. In response to the field strength detecting circuit (8), a soft muting control circuit (10) is operated, whereby a muting circuit (7) gradually mutes the output signal of a detector circuit (6). Furthermore, an alternate current signal detecting circuit (12) detects the alternate current signal component included in the output signal from the field strength detecting circuit (8), whereby the occurrence of multipath reflection interference is detected.

Abstract: A scanning radio is provided having a plurality of the following elements: 1. a circuit to develop an output representative of the noise power contained in a demodulated signal at a present time; 2. a circuit to delay the output of (1) thereby generating an output representative of the noise power contained in the demodulated signal at a past time; 3. a comparison circuit to compare the output of (2) with the output of (1) to develop an output indicating decreasing noise power and therefore improving signal quality; 4. a comparison circuit to compare the output of (2) with the output of (1) to develop an output indicating increasing noise power and therefore degrading signal quality; 5. a comparison circuit to compare the output of (1) with a reference level to develop an output indicating noise power above/below a threshold and therefore signal strength below/above a corresponding threshold; 6. control processor responsive to outputs (3), (4), and (5) to control local oscillator generator; 7.

Abstract: A method and circuitry for reducing noise is provided. The circuit receives a digital data signal at its input (26). The signal is input to a magnitude evaluator (28) and a pass/squelch circuit (30). Magnitude evaluator (28) samples the digital signal and controls an integrator (36) according to the magnitude of each of the samples. Integrator (36) averages the magnitudes over time. If the signal is a noise signal, integrator (36) toggles a switch (40) to activate pass/squelch circuit (30) to squelch the digital data at its input (29). If the signal is a valid signal, then integrator (36) toggles switch (40) to deactivate pass/squelch circuit (30) to allow the digital data to pass therethrough to destination device (44).

Abstract: A noise component is extracted either from FM-detected output or from the so-called signal meter in the intermediate frequency amplifier. The noise component is amplified and rectified to provide a d-c signal indicative of the noise level. The rectified noise is then shaped to produce a control signal having a predetermined level and a width. The control signal is supplied to the gate circuit to control the opening and closing of the gate through which the FM detected output passes. The gate is closed during a period when the pulse noise is superimposed on the FM detected output, and is opened during a period when the pulse noise is not superimposed to the FM detected output. In the mean time, the rectified d-c signal is smoothed out to be used as a control signal for controlling the stereo separation, the attenuation of high frequency component of the MPX-demodulated audio outputs, and the overall signal level of the audio outputs.

Abstract: To reduce noise-ups, a radio receiver includes a comparator which is electrically connected to a variable potential to set a threshold voltage and connected to the IF circuit of the radio for comparison. The output of the comparator is applied to voltage controlled resistance circuits so that as the strength of the signal drops below the threshold value, the resistances are reduced. These reduced resistances are in shunt with a filter resistor so that as the resistance drops, the frequency response of the filter is lowered. Signals from the IF stage are passed through the filter before being transmitted to the audio stage so that as the signal strength drops below the threshold value but before a complete dropout, the frequency response is lowered.

Abstract: An improved method of statistically determining the presence of noise on an FM communications channel permits digital signal processing techniques to more reliably squelch unnecesssary segments of an FM receiver reducing noise and power consumption. Digital samples of an FM signal having real (in-phase) and imaginary (phase quadrature) components representing the real and imaginary components of a phasor rotating about the origin of a Cartesian coordinate system at a rate indicative of a signal on the channel are mathematically operated on. Successive digital samples are multiplied by the complex conjugate of temporally adjacent samples producing a new stream of phasors representative of the phase change between samples. The phase changes between samples are processed to produce a number that indicates the probability of the channel having noise present.

Abstract: A clock-driven pulse source is used to apply repetitive short pulses to the squelch control connection point of the squelch circuitry of a radio receiver to deactivate momentarily the squelch circuitry at regular intervals. 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. This radio receiver operational checking system may also be utilized where there are two or more radios in use by providing an additional clock-driven pulse source for each radio in use. The system may be arranged so that the status of individual radios may be quickly ascertained by sound and/or by light indicators.

Abstract: A channel discriminator circuit is specifically adaptable for use in association with a radio receiver in which DC voltage signals are generated which are proportional to the FM signals received by the radio receiver and an inhibit circuit will generate an inhibit signal denoting the reception of FM signals above a predetermined detection threshold corresponding to an assigned carrier frequency. The channel discriminator circuit will determine whether the FM signals received are centered within a predetermined band width corresponding to the assigned carrier frequency by comparing the DC voltage signal generated with upper and lower reference voltage limits generated by a potentiometer network and will cause the inhibit circuit to generate an inhibit signal only if the DC voltage representing the FM signal received is within the predetermined limits established by the potentiometer network.

Abstract: A circuit for decoding coded frequency modulated signals eliminates perturbing effects of noise pulse signals by coupling the signal to be detected through a filter having a transfer function that is related to the conjugated transfer function of the frequency modulation deemphasis filter, the spectrum of the noise pulse, the spectral power density of the signal to be demodulated, and the spectral power density of the noise. A comparison circuit provides the signal at the output of the filter when the output signal exceeds a threshold level. A decision circuit, which provides signals representative of the temporal position and polarity of the noise pulses to the correction circuit, is coupled between the comparison circuit and a circuit for generating noise correction pulses. The noise correction pulses are coupled to the decoder with the output signal of the detector to eliminate the effects of the noise pulse.

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: Reception or non-reception of a signal is detected on the basis of whether or not a certain noise level is reached at the receiver output. Measuring periods are formed, during each of which the charge of a capacitor changes from a fixed value to a value dependent upon the momentary noise. The time from the beginning of the measuring period until a certain state of charge is reached is compared with a reference time, and a receive criterion is produced when the time dependent upon the noise is shorter than the reference time. The reference time may be obtained in a manner similar to the way in which the first-mentioned time is produced. When both times are thus obtained in an analogous manner, not only the presence but also the absence of a signal can be detected much more rapidly than heretofore.

Abstract: A squelch trigger circuit for use in an RF receiver for receiving a modulated carrier signal having a predetermined information band, and producing a squelch trigger signal. The squelch trigger circuit includes a bandpass filter connected to receive the modulated carrier signal and having a passband that includes the information band. The output of the bandpass filter is connected to an AGC circuit that includes a detector for producing a detection signal indicative of the level of the AGC output signal. The detection signal is input to a high pass filter having a corner frequency selected such that the noise signal includes only frequency components higher than one-half of the passband of the bandpass filter, such that the noise signal produced by the high pass filter corresponds to the out of band noise components of the AGC output signal.

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: A multiplex sound receiver in which a detection signal is extracted from a broadcast to indicate whether the broadcast is monaural, stereo, or multi-lingual. The detection signal is used for controlling the separating of the channels. According to the invention, the detection signal is processed in accordance with the strength of the broadcast or the noise level. For instance, the detection signal is integrated over a period that is increased when the field strength decreases.

Abstract: Apparatus for estimating noise in an electrical signal having substantially redundant recurring intervals includes circuitry for producing difference samples corresponding to signal differences between the recurring redundant intervals. A number of difference samples are averaged, and ones of the difference samples contributing to each average are subtracted from the averages. Magnitude values are extracted from the differences between the averages and the difference samples. A predetermined number of the magnitude values are averaged to produce a noise estimate signal.

Abstract: A noise eliminating signal compensation circuit in an audio device such as a car radio is configured to produce a compensation signal having the same frequency and level as those of an entered signal for signal compensation during noise removal, so as never to degrade its signal compensation capacity during noise removal when the switching time for noise removal is relatively long with respect to the wavelength of the entered signal.

Abstract: A safety device to prevent a vehicle-loaded electronic equipment from malfunctioning due to an influence of the high-level electric field. An antenna pattern for detecting the electric field is formed on the same printed board as the electronic equipment, and an electric signal level of the output from the antenna pattern is determined. When the determined level reaches a level at which the electronic equipment may malfunction, the equipment is forcibly controlled toward a safety range of operation.

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 squelch signal generator is responsive to a digital input signal (IN) which causes a display of an eye pattern in an oscillascope. The pattern has at least one eye at each time instant appearing at a predetermined period. A squelch threshold level (V.sub.S) is preselected outside of a predetermined one of uppermost and lowermost cross-points of at least one eye. The squelch comparator compares an input level of the input signal with the first squelch threshold level to produce a resultant signal which is representative of a first result of the comparison. The resultant signal is processed at each time instant by a processing circuit into a squelch signal when the input signal is classified into an undesired signal. An additional squelch threshold level may be preselected outside of the other of the uppermost and the lowermost cross-points.

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 circuit for detecting existence of an information signal comprising an input circuit provided for supply with the information signal, a clamp circuit for clamping a signal obtained from the input circuit to a predetermined fixed DC level, a level detector for detecting the amplitude level of an output of the clamp circuit and for producing a DC output with its level corresponding to the detected amplitude level, and a level comparator for comparing the DC output from the level detector with a predetermined reference voltage to produce an output signal assuming a first level when the DC output is higher than the reference voltage and a second level when the DC output is lower than the reference voltage. The first level or second level of the output signal from the level comparator indicates that the information signal is supplied to the input circuit.

Abstract: The interpolation device for the voice coded in DELTA transmission and transmitted on a fixed frequency or with frequency jumps carrier, comprises in parallel on a classic reception network, a jamming detection device being able to be constituted by a high-pass filter in order to detect the components outside the modulated signal band, a detector circuit with threshold fixing the level of the outside band components characterizing a jamming and possibly a monostable circuit. It comprises, furthermore, a rumbling generator that transmits to the input of the DELTA decoder a rumbling sequence in place of the sequence detected on a stage when this sequence is reckoned as jammed by means of a switch controlled by the output of the monostable circuit.

Abstract: A noise eliminator mounted from the exterior to a flat cable connecting an electric circuit to thereby bypass noise conducting through the flat cable.Feedthrough capacitors are provided at a substrate, feedthrough terminals to be inserted into the capacitors are held by an insulator, at the upper ends of the feedthrough terminals are provided sharp furcate insulation displacement connection portion, and a cover insulator jig for press-inserting the furcation of each insulation displacement connection portion into the flat cable is provided.The sharp furcation of each insulation displacement connection portion pierced into the flat cable nips each cable conductor to be electrically conductive and the cover insulator and insulator are fixed by a holding means to keep the cable conductor and insulation displacement connection portion in conductive condition, whereby noise conductive through the flat cable is bypassed by the feedthrough capacitors.

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: 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: 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: 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 arrangement for suppressing the audible effects of operating supply voltage transients developed when a sound reproducing system including a gain controlled audio amplifier is initially energized and de-energized. A control path supplies the amplifier with a gain (volume) control voltage of positive and negative senses corresponding to maximum and minimum sound volume. A first capacitor is coupled between the control path and a source of positive operating voltage from which the gain control voltage is derived. A normally non-conductive threshold conduction device and a second capacitor are coupled in series with the first capacitor between the control path and ground. The threshold device is biased to be rendered conductive for coupling positive-going supply voltage transients away from the control path via the second capacitor when the system is initially energized, thereby suppressing the audible effects of the positive transients.

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: A CLIMAX-network-compatible receiver with squelch capability comprises a demodulator for processing RF and IF, a squelch gate in the intelligence processing channel, and squelch gate control circuitry connected between the demodulator IF (or demodulator RF) and the squelch gate. In the control circuitry, a swept band (i.e., swept frequency) type of spectrum analyzer receives the demodulator IF and outputs a waveform whose envelope represents all the frequency components in the tested IF band. The detected envelope of the analyzer output is next treated by a compression-effecting log amplifier whose output is then tested by two different detectors for carrier attributable content and noise attributable content. The outputs of the two detectors are differenced and such difference is used to control the gate. The log amp ensures that the gate is controlled in accordance with the ratio of IF carrier to IF noise, regardless of whether IF gain variations change the difference between IF carrier and IF noise levels.

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: 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: An FM receiver including a noise suppressing circuit in which the signal from which the noise is detected is taken from a front-end section of the receiver and a correction to the noise is made prior to the detector of the receiver. The noise is suppressed by terminating the received signal upon detection of the presence of noise and holding the level which was present before the noise was detected for a predetermined period of time. By detecting the noise in a signal from the front end of the receiver and by making the correction prior to the detector circuit, only a very short predetermined time period need be used and no complicated pilot signal processing circuit is required.

Abstract: A noise eliminating circuit capable of detecting a frequency component largely contained in a pulsive noise from an input signal and cutting off a signal path upon detection of such a frequency component for eliminating the pulsive noise, which circuit is characterized by means for keeping the signal path cut off for the duration when the input signal exceeds a preset level.