Abstract: A method for IF bandwidth switchover and an IF bandwidth switchover apparatus in an AM radio receiver are described. This kind of switchover is appropriate if radio transmitters not only transmit at the normal modulation bandwidth but also broadcast programs with an expanded bandwidth. To obtain optimal reception, the switchover is performed as a function of the reception conditions. To this end, the error rate of supplemental AM information, adjacent-channel interference and the signal strength can be evaluated. These criteria can be used either individually or in various combinations.

Abstract: A radio receiver having a variable bandwidth received channel filter (113,115) to reduce interference is disclosed. A interference is detected by comparing received signal strength and received signal BER. The bandwidth of the filter (113,115) is narrowed to improve BER when a received signal strength is greater than a threshhold value and BER is worse than a threshhold value.

Abstract: An FM receiver includes an IF unit followed by an LF unit, the IF unit having an IF filter arrangement. The center frequency of the IF filter arrangement, which is relatively narrowbanded with respect to the channel bandwidth, is controlled as a function of receiving conditions. The receiver has circuitry for changing the signal transmission characteristic of the IF and/or LF unit, including a detector module for detecting signals characterizing various receiving states, a signal processing unit which changes the amplitude or the time values of signals from the detector module, and a signal linkage unit to create output signals by way of logic and/or time dependent linkage of signals outputted by the signal processing unit.

Abstract: Multiple simultaneous uses of a multi-service digital receiver are made possible with a single practical analog-to-digital converter by translating the various service bands in frequency to form a single, generally continuous composite service band in which substantial frequency gaps between the different services are eliminated. Bandwidth requirements are further reduced by a bandfolding technique in which at least one service waveband is divided about an intermediate mixing frequency, the divided portions are overlapped so that they collectively occupy a sub-waveband with a smaller bandwidth than the original band, and the mixing frequency is chosen such that user-selected frequencies do not interfere with other active frequencies. Interference between non-selected active frequencies is permissible and simply ignored.

Abstract: Automatic gain control of a communications receiver is provided by including a filter in the upper end thereof having a frequency pass-band which slopes off at each end and can be controllably shifted in a direction and by an amount determined by a control voltage which corresponds to the output signal level. As a result of such shifting of the frequency band relative to the frequency of a received signal, the filter provides adequate gain reduction even for unduly strong received signals and with less signal distortion and lower power consumption than occurs with AGC circuits which operate by changing the bias of a gain control amplifier. If the receiver employs a PLL with a voltage-controlled oscillator, the VCO control signal can be combined with the gain control voltage so as to control the center frequency of the filter pass-band as well as the amount by which it is shifted in order to provide gain control.

Abstract: A filter equipment comprises a plurality of filters, which are connected in cascade or in parallel. Characteristics of each filter are controlled according to an applied current. Desired characteristics can be realized by a relatively simple circuit configuration. The filter is controlled to adapt to PAL or NTSC standards, for example.

Abstract: An FM receiver includes an IF unit followed by an LF unit. The receiver has circuitry for changing the signal transmission characteristic of the IF and/or LF units, including a detector module with detector circuits for detecting values characteristic of receiving or interference states, with the inputs of these detector circuits each being connected with a circuit point of the IF or LF unit carrying the signal to be processed and with the outputs of these detector circuits providing signal characterizing receiving the interference states.

Abstract: A radio receiver responsive to a received RF signal containing a plurality of channel frequencies each having broadcast information which includes a circuit for producing a wide band version of the received RF signal and a circuit for producing a narrow band version of the received RF signal. Selection of a channel at a given frequency is accomplished by using the wide band version of the received RF signal and after such selection is made, the narrow band version of the signal is used for further reception of the selected channel frequency and reproduction of the information thereon.

Abstract: A relay receiver performs a heterodyne relay operation by using a receiving frequency converting portion, an intermediate frequency amplifying portion and an automatic gain controller. The variable band limiting portion limits an amplified signal output from the intermediate frequency amplifying portion to a band corresponding to the state of a band control signal, thereby transmitting an amplified signal. The band control portion is responsive to an automatic gain control signal outputted from the automatic gain controller, and outputs to the variable band limiting portion a band control signal for enabling the variable band limiting portion to limit the amplified signal to a narrow band in accordance with a decrease in the arriving level of the high frequency band received signal. Therefore, the frequency band of a communication signal amplified by the intermediate frequency amplifying portion is narrowed only when the arriving level of a received signal is low.

Abstract: A radio receiver is disclosed having a wide filter and a narrow filter, each of which is connected with the front end and outputs an intermediate frequency signal. To the output of the filters are connected first and second detectors, respectively. A subtracter receives the outputs of the detectors and subtracts one from the other. A switch receives the output of the subtracter and directs the outputs of detectors in such a way that the switch is switched to a first position for directing the demodulated output from the first detector to a following circuit when the difference is below a reference level, and to a second position for directing the demodulated output from the second detector to the following circuit when the difference is above the reference level.

Abstract: A direct conversion receiver having a tri-phase architecture including three separate baseband signal channels. RF communications signals which are being tuned by the receiver are split into three equal and in-phase components which are mixed with three equal but substantially out-of-phase injection signals on frequency with the communications signal. The resulting baseband component signals are independently filtered and amplified on the three signal channels. The baseband components are then directed to a signal processing unit which corrects the baseband components for gain or phase mismatch errors between the signal channels based on the information carried by the three components and thereafter demodulates the signals in order to acquire the information carried by the RF communications signal. An automatic gain control system and a signal filtering system adapted for use with direct conversion receivers are also disclosed.

Abstract: An apparatus for receiving broadcast FM waves using an FM (Frequency Modulated) detector is disclosed in which an output signal level of an automatic gain controller (AGC) is controllable so that when the C/N ratio is reduced and the output level of the automatic gain controller is reduced, the loop gain of a PLL type FM demodulator is accordingly reduced and response is delayed with the bandwidth being narrowed . Therefore, since delayed threshold extension is applied thereby, no signal noise, such as white points appearing on an image screen, will occur.

Abstract: In an FM receiver where the center frequency of an IF filter is varied depending on the received signal, an arrangement is described in which the passband of the retuned IF filter is selected so that a distinct resonance region having a relatively steep-edged drop of at least 6 dB exists in the middle of the channel; a less steep or level curve exists in a region essentially symmetrically spaced from the middle of the channel on both sides of the resonance region; and the pass limits lie essentially in symmetry with the middle of the channel.

Abstract: A TVRO receiver for receiving frequency-modulated video signals comprises a tuner including a super-heterodyne circuit having a voltage-controlled oscillator (VCO), means for supplying a cotnrolling input voltage to the VCO, and a mixer for combining incoming 1st intermediate frequency (IF) sigals within a 1st predetermined IF frequency range with the output of the VCO to reduce the frequency of the 1st IF signals to generate 2nd IF signals within a 2nd predetermined IF frequency range, and a filter for selectively rejecting undersired interference signals. The interference filter comprises separate trap means for respectively blocking out interfering signals having selected bottom and top trap frequencies, tuning means for adjusting the bottom and top trap frequencies, means for increasing the quality factor of the trap means, and means for selectively switching the trap means into and out of the receiver based on the presence or absence of signals which interfere with the received signals.

Abstract: A phase locked loop utilizing digital techniques to control the closed loop bandwidth of the RF carrier phase locked loop in a receiver provides high sensitivity and a wide dynamic range for signal reception. After analog to digital conversion, a digital phase locked loop bandwidth controller provides phase error detection with automatic RF carrier closed loop tracking bandwidth control to accommodate several modes of transmission.

Abstract: The adaptive filter for frequency modulation of the present invention utilizes an audio tone multiplexed into the baseband modulation spectrum as a pilot tone to control and determine the amount of adaptation of the effective and variable bandwidth of the filter for optimum selectivity and rejection of wideband interference or narrowband offset interference. The multiplexed tone is detected and the filter is adjusted according to the signal-to-noise ratio of the detected tone. A continuous and adaptive decrease or increase in bandwidth is produced to accommodate the actual signal bandwidth to achieve rejection of interference with minimum distortion. Additionally, the filter compensates for transmitter drift of center frequency. This filter may be used at radio or intermediate frequencies.

Abstract: A radio receiver having a frequency converter which frequency converts an RF signal into an IF signal. An IF filter filters the IF signal to provide the filtered output to a frequency discriminator. The discriminator frequency discriminates the filtered IF signal to produce a baseband signal. From the baseband signal, a voice signal is recovered and a data signal is extracted. Using the IF signal, a field detector detects an electromagnetic field strength of RF signal and outputs a signal detect signal when the field strength is higher than a predetermined level. A sync detector detects a sync signal in the extracted data signal and sync detect signals, a controller controls the bandwidth of IF filter so that the S/N ratio of the recovered voice signal is increased and the error rate of the extracted data signal is decreased.

Abstract: A calibration circuit for a linear channel of an optical modem includes circuitry interconnected to the linear channel for causing the linear channel to oscillate. Circuitry is interconnected to the output of the linear channel for monitoring the bandwidth of the linear channel during oscillation and for generating output pulses. The output pulses are counted and are utilized for generating an adjustment signal applied to the linear channel for adjusting the bandwidth of the linear channel.

Abstract: A RF paging receiver which is tunable to channels to receive pages comprising characters to be displayed with the pages being transmitted in a plurality of licensed frequency bands with each band containing a plurality of FM channels in which signal strength of pages on received channels in the bands varies as a result of variable antenna gain with programming of channels being accomplished by channel programming commands in accordance with the invention includes a tunable antenna (12, 14) having a reception bandwidth spanning the frequency bands with the antenna being tunable in response to an antenna tuning signal to achieve maximum antenna gain for a received channel in any one of the plurality of licensed frequency bands; a RF tuner (16), coupled to the tunable antenna, for receiving individual channels from the bands in response to varying a receiver tuning signal specifying reception of one of the channels within the plurality of frequency bands, the RF tuner comprising a plurality of RF amplifiers (102

Abstract: A paging receiver has a synthesizer for governing the receive frequency. The paging receiving further has characteristics which are varied in response to the receive frequency. These characteristics include varying the bandwidth of a loop filter within a phase lock loop within the synthesizer as well as varying the time in which a detector circuit used to extract a DC level from a recovered audio signal is disabled. Furthermore, the bandwidth of the loop filter is varied in response to switching from a first receive frequency to a second receive frequency in order to provide for either a uniform frequency lock time or for a rapid frequency lock time. Furthermore, the time in which the detector circuit is disabled is correspondingly changed.

Abstract: In this radio receiver, the charge on a capacitor (14) controls the bandwidth of filters in the receiver's audio circuits. When tuning the radio, a bandwidth control circuit (13) forces this capacitor (14) to discharge, thereby forcing the audio path to be bandwidth restricted, thereby minimizing interstation noise reproduction.

Abstract: An FM tuner including a PLLFM demodulation circuit is provided, which selectively employs one of two BPFs having different extraction bandwidths as an IFBPF. This FM tuner is configured such that by employing a relationship between a lock range and an input signal level of the PLLFM demodulation circuit, an optimum value of the lock range of the demodulation circuit is set for a bandwidth of an input signal, even if any of the BPFs is selected. When the BPF having a narrower bandwidth is selected as the IFBPF, a signal to be inputted to the PLLFM demodulation circuit is attenuated to decrease the level of the input signal of the demodulation circuit to be lower that the level when the other BPF with a larger bandwidth is selected as the IFBPF. As a result, a lock range width of the PLLFM demodulation circuit is reduced.

Abstract: In a tuner circuit in which a plurality of band signals are received by a single common high frequency amplifier stage, a band switching circuit switches a resonant circuit to .lambda./2 type when the amplifier stage receives the highest band signals and to .lambda./4 type when the amplifier stage receives band signals other than the highest band signals.

Abstract: A method and arrangement for electronically bandswitching a radio (100) is described which includes at least a receiver (110, 111), a PLL (120), and a fully synchronized, programmable counter as a frequency divider (140) that is coupled between the receiver and the PLL. This fully synchronized divider (140) provides an output signal (143) at a lower frequency with minimal harmonic energy and improves the sideband noise performance as the divisor increases. When the radio also includes a transmitter (104), stepped attenuators (128, 132) are also included for adjusting the modulation of the PLL (120) when in the transmit mode.The PLL includes at least a reference signal generator (121, 122), a phase detector (124), and a voltage controlled oscillator (127) having an output (129) coupled, via a feedback path, to a second input (131) of the phase detector (124).

Abstract: A TVRO receiver for receiving frequency-modulated video signals, the receiver comprising a tuner including a superheterodyne circuit having a voltage-controlled oscillator (VCO), means for supplying a controlling input voltage to the VCO, and a mixer for combining incoming 1st IF signals with the output of the VCO to reduce the frequency of the 1st IF signals to a 2nd IF frequency which is sufficiently high to permit the output frequency of the VCO to be above the frequency range of the 1st IF signals, and a linear phase passband filter for passing a single video channel in the 2nd IF output from the mixer, the filter producing an output which is at least about 10 dB down from its peak at both +10 MHz and -10 MHz from the center of the passband of the filter.

Abstract: An audio processor for adaptively rejecting undesired noise and interference in an audio input which includes a variable Q, 10 kHz switched capacitor notch filter. The Q of the notch filter is varied by a control loop responsive to the 10 kHz content of the audio signal. The notch filter includes a summer section that is clocked at a predetermined frequency, and an integrator section which is clocked at a multiple of the predetermined frequency in order to prevent center frequency variation with changes in Q of the notch filter.

Abstract: Multi-channel telephone communication is enhanced by the use of the adaptable threshold extension demodulator described in this patent. These devices permit adjustment of the threshold depending on the present loading of the baseband. By changing the characteristics of the feedback loop in the demodulator, the threshold can be adjusted for optimal performance. The sensor may take one of two forms. In a first embodiment, the sensor detects baseband loading by converting the baseband to a DC level. In another form, frequency selective filters determine the highest level of the baseband and convert that into an incremental level signal. In a variation of the second embodiment, a low-pass filter and a bandpass filter detect the loading directly from the IF signal.

Abstract: An improved TVRO receiver for receiving signals broadcast over a plurality of channels with varying bandwidths and having a tuner producing output signals corresponding to the received signals and having bandwidths which vary from channel to channel is provided with a band pass filtering arrangement receiving the output signals and having a controllably adjustable pass band, a bandwidth detection circuit for receiving the output signals passing through the filtering arrangement and being responsive to a current output signal corresponding to the channel being received for producing a control signal indicative of the extent of deviation of the bandwidth of the current output signal beyond the current pass band of the filtering arrangement, and a control circuit responsive to the control signal for adjusting the pass band of the filtering arrangement to accommodate the bandwidth of the current output signal corresponding to the channel being received, if the bandwidth deviation of the current output signal exce

Abstract: A carrier-tracking FM demodulator system for providing threshold extension relative to the demodulation of an FM signal, such as a television signal, is disclosed, wherein an effective system filtering response tracks the instantaneous carrier frequency of the FM signal, without frequency compression, utilizing filters of substantially fixed-tuned characteristics. The waveform fidelity of the demodulated output signal is substantially independent of the action of the carrier-tracking feedback control loop utilized in the demodulator system. In order to track the instantaneous carrier frequency, the invention employs a number of mixer means, in cascade, each of which is utilized in conjunction with a local-oscillator means or other local-carrier-frequency generator means.

Abstract: This invention relates to a digital audio tape recorder using a rotary magnetic head. On the tape which has been recorded using R-DAT, signals forming to the industry standards are recorded at a standard tape speed. The tape is caused to run at a speed faster than the standard tape speed and the recording signal is subjected to high speed reproducing while maintaining the rotational frequency of the head at a rotational speed at the time of recording.

Abstract: A TVRO receiver for receiving frequency-modulated video signals, the receiver comprising a tuner including a superheterodyne circuit having a voltage-controlled oscillator (VCO), means for supplying a controlling input voltage to the VCO, and a mixer for combining incoming 1st IF signals with the output of the VCO to reduce the frequency of the 1st IF signals to a 2nd IF frequency which is sufficiently high to permit the output frequency of the VCO to be above the frequency range of the 1st IF signals, and a linear phase passband filter for passing a single video channel in the 2nd IF output from the mixer, the filter producing an output which is at least about 10 dB down from its peak at both +10 MHz and -10 MHz from the center of the passband of the filter.

Abstract: A compressed single side band communication system and method in which the audio signal is compressed prior to pre-emphasis and thereafter summed with a pilot tone for further compression prior to transmission. Initially, only the pilot tone is transmitted at full rated power to aid in acquisition of the signal by the receiver. Thereafter, the transmitter ALC is disabled and the pilot tone is attenuated. The receiver adjusts the frequency characteristics of the pilot tone filter and phase lock loop filter in the detector as a function of lock-on. The delay after loss of lock-on in reverting to wide band pilot tone and wideband loop filters is varied as a function of signal strength. The pilot tone may be frequency modulated for tone coded squelch, with the modulating source being located in the return end of the phase lock loop filter. A unique filter is provided to insure acquisition of the pilot tone.

Abstract: A receiver is provided for a television system which uses time division miplexing (TDM) of analog image signals and of bursts of duobinary coded digital data signals. The digital data signals are transmitted during the line and frame blanking intervals and grouped together in packets, comprising the sound and synchronization signals, the spectral width required by the analog part being greater than that required by the digital part. The receiver comprises a common frequency demodulator for the analog and digital signals, adaptive as a function of the signal-to-noise ratio after demodulation as a width less than the width which is optimum for the analog part when the latter has a high signal-to-noise ratio. The demodulator has an input filter which is either analog or digital and may be adjusted in response to the error rate.

Abstract: A FM demodulator system which provides threshold extension by frequency selective phase modulation of the input FM signal in a band pass filter to reduce phase error between the input and output of the filter. The output of the filter is applied to an FM discriminator which provides a base band signal. This base band signal is applied to a frequency selective phase compensation network to derive a signal which phase modulates the band pass filter. The filter rejects uncorrelated thermal noise so as to effect threshold extension in the demodulator system.

Abstract: A radio receiver includes a first tuner, a first intermediate-frequency amplifier, at least two intermediate-frequency filters connected between the first tuner and the first intermediate-frequency amplifier and having difference frequency bands, a switching circuit for applying an output signal from the first tuner through a selected one of the intermediate-frequency filters to the first intermediate-frequency amplifier, an automatic gain control circuit for controlling the gain of the first tuner, a first phase-locked loop for enabling a local oscillator in the first tuner to oscillate at a frequency dependent on the frequency of a desired channel, a second tuner, a level detector circuit for detecting the level of an output signal from the second tuner, a second phase-locked loop for enabling a local oscillator in the second tuner to oscillate at a prescribed frequency, and a controller for controlling the first phase-locked loop to enable the first tuner to receive and issue a desired signal from a desire

Abstract: A radio receiver from antenna to detector designed to be realized substantially on an integrated-circuit chip comprises a single tunable oscillator and a plurality of mixers. An input signal from an antenna is connected as an input to a first mixer and mixed with a signal derived from the oscillator. The signal may be taken directly, may be multiplied to a desired level or may be divided to a desired level. A particular output from the first mixer is selected by a first tunable filter. The output of the first tunable filter is taken as an input to a second mixer where it is mixed with a second signal derived from the oscillator. The process of mixing and application of the mixed signal to a tunable filter to select a desired frequency is continued as needed until the signal is reduced to a desired intermediate frequency range where it is amplified as needed to a level sufficient to drive a discriminator.

Abstract: The threshold level for demodulating an FM signal, for instance a television picture signal, has been improved or lowered by adaptively restricting the bandwidth of the signal using an adaptive bandpass filter, and therefore, the picture quality and/or S/N ratio of the demodulated television signal has been improved. The adaptive bandpass filter has enough bandwidth when the signal level is sufficiently higher than the threshold level, but is narrow when the signal level is close to or lower than the threshold level. The bandwidth of the adaptive bandpass filter is adjusted according to the total power of the input FM signal and C/N (the carrier signal to noise) ratio. The improvement of the threshold level is almost 2 dB.

Abstract: A television bandwidth correcting system for use with a television receiver or television tuner in which the quality of the displayed picture, defined by the bandwidth of the video signal, is accurately maintained for all input signal levels. Video and audio components are extracted from the intermediate frequency signal produced at the output of a bandwidth adjusting circuit. The levels of the extracted video and audio components are compared, and the result fed back to a bandwidth controlling input of the bandwidth adjusting circuit.

Abstract: A compressed single side band communication system and method in which the audio signal is compressed prior to pre-emphasis and thereafter summed with a pilot tone for further compression prior to transmission. Initally, only the pilot tone is transmitted at full rated power to aid in acquisition of the signal by the receiver. Thereafter, the transmitter ALC is disabled and the pilot tone is attenuated. The receiver adjusts the frequency characteristics of the pilot tone filter and phase lock loop filter in the detector as a function of lock-on. The delay after loss of lock-on in reverting to wide band pilot tone and wideband loop filters is varied as a function of signal strength. The pilot tone may be modulated for tone coded squelch. The modulating source is located in the return end of the phase lock loop filter. A unique filter is provided to insure acquisition of the pilot tone.

Abstract: In an FM demodulation circuit which demodulates an FM signal by the use of a phase-lock loop constructed of a phase comparator, a loop filter and a voltage-controlled oscillator, the loop filter is a variable loop filter whose loop band width is varied in correspondence with the modulation band width and the carrier/noise ratio of the input signal by a base band processing circuit.

Abstract: The invention relates to a superheterodyne circuit characterized by comprising a first mixer converting a received signal into the first intermediate frequency, a second mixer converting the first intermediate frequency into a second intermediate frequency, and a product detection stage demodulating the second intermediate frequency to an audio frequency, by having a constitution wherein the local oscillation of the first mixer is input from a VCO for which a PLL circuit is used, wherein the local oscillation of the second mixer is an output obtained by mixing the frequency of a second oscillator with that of a third oscillator in a fourth mixer, wherein the second oscillator combined with the frequency of the VFO in the sixth mixer, alone or in further combination with the frequency of the output of a BFO input via to the product detection stage is the frequency of the third oscillator or an output obtained by mixing the frequency of the third oscillator with a frequency obtained through the frequency divisi

Abstract: In a radio receiver a multipath fade compensating circuit comprises a single-pole filter circuit the center frequency and Q of which are controlled in dependence upon the amplitudes of signal components in narrow frequency bands within the band of frequencies passed by the filter circuit. The narrow bands may be selected from an array by a microprocessor, or may be derived using variable frequency filters.

Abstract: The demodulator combines a conventional frequency discriminator with a bandpass filter for removing the noise which is present from the band occupied at a given instant by the modulated signal. The center frequency of the bandpass filter is controlled in dependence on the instantaneous frequency of the modulated signal and its bandwidth b.sub.u is controlled in dependence on the instantaneous width of the band occupied by the modulated signal.

Abstract: In an AM radio signal receiver, the value of Q of the input tuning circuit is varied in accordance with information indicative of the magnitude of the received signal. This information may be derived from the intermediate frequency (IF) signal processing stage of a superheterodyne receiver. In such a case, the IF signal is applied to a narrow-band filter having a pass band which is narrower than that of the IF signal processing stage. The amplitude of the output signal from the narrow-band filter is then detected to control a variable resistance element which is connected in parallel with winding of an input tuning coil so that the value of Q of the input tuning circuit is lowered when receiving a broadcasting signal having relatively high intensity. The invention may be adapted to an AM stereo receiver. In this case, the variable resistance element is controlled by both a signal indicative of the amplitude of the received signal and a signal indicating that the received signal is a stereo signal.

Abstract: A circuit arrangement provides that false lock-in of the phase locked loop caused due to noise in a radio channel given pre-emphasis and de-emphasis is avoided and short transfer times can be obtained between the individual channels. To this end, a full-wave rectifier has a following transfer switch connected to a frequency shift keying demodulator having a phase locked loop. A high-pass filter is connected as a compensation filter in one branch and the incoming frequency shift keyed signal is directly connected to the demodulator over a second branch after it has been recognized.

Abstract: A frequency hopping spread spectrum demodulator includes a broad band filter covering the spread spectrum bandwidth and a narrow band filter which can be selected to pass any one of a number of subbands making up the spread spectrum bandwidth. The filter is switched from broad to narrow band in response to determination of synchronization acquisition. Synchronization acquisition itself is accomplished in one embodiment by summing the outputs from a plurality of channels each selectively receiving one of a number of predetermined hopping frequencies, and threshold-comparing the summed signal to test for synchronization. In an alternate configuration, the received signal and a local reference signal are correlated, the correlated signal is integrated, and the integrated signal is then compared to a threshold, with synchronization being determined when an output from either one of the threshold comparator or integrator is present.

Abstract: The filter has a fixed Q and is coupled to a source of AC signals. A source of pulses is applied to a variable-voltage circuit, the circuit being responsive to each pulse to produce a threshold voltage which varies from a first value toward a second value. A comparator circuit has one input coupled to the filter and a second input coupled to the variable voltage circuit. The comparator produces a signal for a duration related to the time the amplitude of an AC signal from the filter is at least equal to the threshold voltage.

Abstract: In an amplitude modulation radio receiver a relatively narrow band filter is placed before the receiver detector and a relatively wide band filter is placed just prior to the IF amplifier stages. An IF stage controlled by receiver AGC is designed to have a saturation or clipping level about 6 dB above the normal IF level for that stage. As a result the selectivity characteristic for the receiver will be approximately rectangular and encompass the IF frequency channel if the bandpass of the narrow band filter is chosen to be the IF frequency channel.

Abstract: A circuit having a variable input impedance which is controlled by application of a direct current input signal. The variable impedance circuit comprises a pair of capacitors coupled in series with a pair of diodes. The diodes are rendered conductive in response to the direct current control signal to substantially short the two capacitors in series with one another across the input terminals of the circuit. With no direct control signal being applied to the circuit the diodes are non-conductive which substantially disconnects the capacitors from appearing across the inputs of the circuit. Hence, the reactance component of the input impedance of the circuit is varied in response to the direct control signal.

Abstract: A unidirectional current with i-f variations superimposed thereon is applied to the interconnected emitters of a pair of transistors, the collectors of which are coupled to a succeeding stage by a narrow-band filter and by a wide-band filter respectively. The unidirectional current with i-f variations is amplified by a selected one of the transistors and filtered accordingly, depending upon which of two polarities of potential is applied between the bases of the transistors.