Abstract: An article comprising a micro-machined filter advantageously comprises a micro-machined resonator, a drive circuit and a detection circuit, at least a portion of which are circuits are disposed on the resonator within a magnetic field. In operation, an input signal is delivered to the drive circuit. The resonator is excited to movement by the Lorentz force that is generated as signal current varies. Due to the resonator's movement, a voltage is induced in the detection circuit, which moves with the resonator. Using well-known micro-machining techniques, a resonator can be made that has mechanical resonance frequencies extending into the GHz regime. Under proper conditions, such resonances advantageously exhibit very high Q-values, so that the resonator shows a significant physical response (e.g., movement) over a very narrow range of excitation frequency. When the frequency of the input signal matches such a frequency (i.e., the resonant frequency), the device generates a voltage having such a frequency.

Abstract: A satellite broadcasting receiving tuner having a band-pass filter capable of adequately attenuating and removing disturbing wave components having frequencies in the vicinity of 480 MHz and capable of being easily tuned to the high-end frequency. The tuner has at least the band-pass filter for transmitting a down-converted received satellite broadcasting signal and a frequency converter section for converting the received satellite broadcasting signal transmitted through the band-pass filter into a signal having an intermediate frequency.

Abstract: A system (10) for remote convenience control of performance of a function includes a portable transmitter unit (14) and a receiver unit (18). In one embodiment, the system (10) is a remote convenience vehicle system. The transmitter unit (14) transmits a signal (16). The signal has a RF frequency at an unknown value within a range of values and conveys a message that contains a function request. Within the receiver unit (18) is superheterodyne circuitry (32) that has a mixer (44). The mixer (44) mixes a RF signal (42) coming from an antenna (28) and a reference frequency signal from a reference oscillator (46), and outputs an intermediate frequency signal (50) conveying the message. A bandpass filter (66) filters the intermediate frequency signal to pass a range of frequency values smaller than a known range of intermediate frequency values. Tuning control circuitry (70) automatically adjusting the bandpass range of the bandpass filter (66) to vary the bandpass range over the intermediate frequency range.

Abstract: A double super tuner for receiving television signals from conventional broadcast, CATV, satellite broadcast, and HDTV. A first frequency converter converts an input high-frequency signal in a first intermediate frequency band signal based on a first local oscillator signal. The output of the first frequency converter is band-pass filtered by a dielectric filter. A second frequency converter converts the output of the dielectric filter into a second intermediate frequency band signal based on a second local oscillator signal.

Abstract: The present invention aims to provide a CATV converter which can receive both of analog and digital signals. The CATV converter comprises a second mixer (10) coupled with a first filter (13) which attenuates approximately equal frequency to an audio carrier of an upper adjacent channel and approximately equal frequency to a video carrier of a lower adjacent channel, a first amplifier (14) coupled with an output terminal of the first filter (13), and a second filter (15) coupled with the output terminal of the first amplifier (14). The second filter (15) attenuates a video carrier of the upper adjacent channel and an audio carrier of the lower adjacent channel. When an input signal is within a predetermined frequency range, the input signal fed to the input terminal (1) can short-circuit the input and output terminals of the second filter with a high frequency of the input signal.

Abstract: An RF transceiver operable in two separate frequency bands has transmitter and receiver elements with broadband components to provide a flat frequency response across the two separate operating frequency bands. The broadband transmitting and receiving elements are utilized with other narrow band components which are designed for operating in either the first frequency band or the second frequency band. The use of common components for operating in both frequency bands reduces part count and cost along with reduced size and weight.

Abstract: The receiver includes a ceramic filter which is connected to the output side of a mixer circuit for limiting a band, an intermediate frequency amplifying circuit cascade connected to the output side of the ceramic filter in a plurality of intermediate frequency amplifying stages, and a plurality of passive band-pass filters connected between the respective intermediate frequency amplifying stages of the intermediate frequency amplifying circuit. Thereby, the receiver is able to reduce the size and costs thereof.

Abstract: A double super-heterodyne receiver has a high-frequency input circuit that includes a high-frequency amplifying device, a low-pass filter and a high-pass filter used for obtaining bandpass characteristics for the receiving band. A switching device for changing the cut-off frequency of, at least, the low-pass filter is further provided for the high-frequency input circuit. The switching device is controlled to be on or off in response to the receiving frequency, thereby changing the passband of the high-frequency input circuit. Image disturbance characteristics can thus be improved.

Abstract: There is disclosed a fully integrated television receiver for receiving a standard antenna or cable input and outputting a standard video baseband signal and a standard audio baseband signal. The receiver employs an up-conversion mixer and a down-conversion image-rejection mixer in series to produce an on-chip IF signal. Audio detection of the IF signal is performed via an audio delay-locked loop operating in quadrature to the audio FM signal. Video detection of the IF signal is performed by frequency mixing the IF signal with the extracted video carrier of the IF signal. Variable load drive capability is provided for both the video output and the audio output.

Abstract: In a process for transmitting data in a data processing system and with a data processing system having distributed computer nodes (N) communicating with one another by way of a serial data bus (BUS) between which objects can be exchanged, it is provided that an object transmitted to the bus is tested in a computer node by a plurality of acceptance filters (AF1, AF2, AFm) which each have associated with them at least one receive buffer (RB1, RBn-1, RBn), and that after the receive buffer, the object is stored in a memory (M) associated with a central unit. Through the hierarchical arrangement of the acceptance filters, a freely-selectable association with the receive buffers and a definition as a band pass- or rejection filter, it is possible very flexibly to transmit further only desired objects and thus to provide an optimal configuration for managing the objects of a computer node.

Abstract: A 3-element series parallel resonator, which performs series resonance and parallel resonance at a predetermined frequency by a combination of three elements including an inductor and a capacitor of concentrated constants, is used as a filter. This design can reduce the circuit constant and permits a filter to be formed on a semiconductor substrate. Accordingly, various micro-wave devices, such as an amplifier which requires a filter, a frequency converter, a multiplier and signal switcher, can be designed into an MMIC on a single chip.

Abstract: In a television receiver a SAW filter (FSAW) is preceded by a coupling network (CNW). The coupling network (CNW) includes an inductor (LP) between two input terminals of the SAW filter (IS1, IS2). It further includes a series resonance circuit (SRC) coupled to at least one of the input terminals (IS1). In order to reduce signal distortion a resistor (RP) is coupled between the two input terminals (IS1, IS2). Alternatively, a resistor (RS) is coupled in parallel to the series resonance circuit (SRC).

Abstract: An RF communications receiver permits greater integration on standard silicon chips and consumes less power than previous receivers. Sub-sampling and discrete-time signal processing techniques are used to frequency down-convert, filter, amplify, and select a desired analog RF channel. A sample-and-hold circuit sub-samples the desired analog RF channel of carrier frequency f.sub.c, thereby down-converting it to a discrete-time image signal of frequency f.sub.i. Successive down-sampling, anti-alias filtering, and amplification of the discrete-time image signal yield a low-frequency discrete-time signal containing a down-converted channel of frequency f.sub.k. The low-frequency discrete-time signal is then digitized, filtered, and demodulated to reveal its baseband information content.

Abstract: A radio communication apparatus having a reception system having an automatic gain control circuit, which includes a first band-pass filter with a wide band inserted into a signal supplying passage to a digital demodulator located in the subsequent stage of a variable gain type intermediate frequency amplifier. The automatic gain control circuit further includes a second band-pass filter with a narrow-band set narrower than that of the first band-pass filter, inserted in a circuit that forms an automatic gain control (AGC) loop. Received analog signals are modulated and subjected to digital demodulation by the digital demodulator after passing through the first band-pass filter. Received intermediate-frequency signals which have passed through the second band-pass filter are supplied to a detector provided in the AGC loop.

Abstract: A wireless audible indication system comprising a transmitter and a receiver. An embodiment of the transmitter includes a crystal oscillator which produces a signal having a predetermined audio frequency. A duty cycle limiting circuit limits the duty cycle of the oscillator signal to be less than 25%. The limited duty cycle signal is applied to a radio frequency oscillator to produce an amplitude modulated radio frequency signal. An embodiment of the receiver includes a superregenerative detector which provides wide band detection of transmissions about a carrier frequency. A signal processing circuit formed by a cascade of a crystal filter stage, an amplifier/comparator stage, and a detector stage, processes the signal from the superregenerative detector. A sound generator integrated circuit, which generates an audible signal indicative of reception of a transmitted signal, is coupled to the signal processing circuit.

Abstract: The invention concerns an I.F. filter arrangement in a receiver for receiving FM signals. An I.F. filter arrangement is to be provided which no longer contains the disadvantageous effects of a control loop from which a control value is extracted from the MPX signal to be used for tracking the I.F. filter. The solution according to the invention is an I.F. filter arrangement having a filter device which comprises a defined, in particular, a fixed adjusted bandpass region and at least two outputs having center frequencies staggered with respect to one another or I.F. frequencies staggered with respect to one another at the same center frequency. The signals from the outputs are fed to a weighting device which is regulated by a control value extracted from the demodulated FM signal.

Abstract: An active filter circuit used in a receiver circuit of a cellular telephone or the like has a voltage/current conversion circuit, an integrating circuit and a current dividing circuit. The voltage/current conversion circuit converts an input signal voltage to a signal current. The signal current output by the voltage/current conversion circuit is divided between the integrating circuit and ground. The current dividing circuit divides the signal current output by the voltage/current conversion circuit between the integrating circuit and ground. The current dividing circuit extracts low frequency components of the input signal voltage from the integrating circuit, and adjusts the cutoff frequency with respect to the extracted low frequency components to change the dividing ratio of the signal current output from the conversion circuit between the integrating circuit and ground.

Abstract: A frequency modulation receiving apparatus comprises a signal-converting circuit for converting a signal received by an antenna into a signal consisting of wave clusters having various frequencies, first limiting circuit for limiting those of the wave clusters which have frequencies outside a first frequency range, second limiting circuit for limiting those of the wave clusters which have frequencies outside a second frequency range narrower than the first frequency range, shearing circuit for combining and outputting a ratio of a signal output by the first limiting circuit and a signal output by the second limiting circuit, frequency-demodulating circuit for frequency-demodulating a signal output by the selecting circuit, detecting circuit for detecting whether or not an adjacent interfering wave exists in a signal output by the frequency-demodulating circuit, and for outputting a signal indicating whether or not an adjacent interfering wave exists in the signal, and control circuit for delaying a signal out

Abstract: A novel direct conversion receiver utilizing a sample and hold circuit for subsampling the input signal. The output of the sample and hold circuit is applied to a sigma-delta loop to provide a high speed low resolution data stream which in turn is applied to a decimator which provides a high precision, low data rate signal having quadrature outputs.

Abstract: A wideband RF-to-IF frequency converter providing multiple use of frequency conversion components for many different types of RF input signals. In specific examples, many different types of signals for communication, navigation, and for interrogation are processed through at least partly common frequency-conversion channels. Such RF input signals in the range from approximately 2 MHz to 2,000 MHz are converted to output IF frequencies, such as 1 MHz and 30 MHz, for further processing in the common receiver. Some narrow band signals, after conversion to IF, are subjected to off-center filtering in relatively broadband IF filters. Input RF filters are not used. Among several frequency conversion stages, only one of the local oscillator signals is tunable; but it is made tunable in relatively small, precise steps by using a double phase-locked loop arrangement in the frequency synthesizer.

Abstract: A filter switching circuit for switching between two or more filters. The filter switching circuit may be integrally formed upon an integrated circuit chip and may be advantageously utilized as a portion of a dual bandwidth receiver, such as employed in a radiotelephone, operable to receive both narrowband and wideband signals.

Abstract: The apparatus includes a mobile receiver for digital audio broadcasting. The transmission process is substantially entirely digital and a whole frequency range is used for the terrestrial transmission. The apparatus includes a receiver for a digital radio signal, particularly wherein the filter coefficient is changeable by a control circuit which generates a first value for the filter coefficient to get the real signal component and thereafter generates a second value for the imaginary signal component, whereby with the switching over of the first and second values for the filter coefficient a simultaneous downsampling of the digital signal is performed.

Abstract: An FM receiver (100) that includes a plurality of filtering elements (120-124) that have various center frequencies and bandwidths that adjust to maximize the signal quality of a desired signal (104) recovers the desired signal (104) by inputting the desired signal (104) to each of the plurality of filtering elements (120-124). Signal recovery is performed on an output of each of the filtering elements (120-124) to obtain a plurality of recovered signals. The recovered signals are then measured to obtain a plurality of signal quality metrics for the desired signal.

Abstract: The invention relates to switchable band filter apparatus for switching signals on-board a satellite, enabling signals of different and unforeseeable bandwidths to be switched between multiple input ports and multiple output ports. The invention also provides various payload architectures using such apparatus. Finally, the invention provides methods of implementing such apparatus and architectures for performing transparent switching of signals on-board a satellite.

Abstract: According to this invention, an SAW electric part includes an SAW filter and an SAW oscillator formed on a substrate having the same temperature characteristics as those of a substrate on which the SAW filter is formed. A frequency converter includes the SAW electric part, a second local oscillation circuit, a frequency converter, a first mixer, and a second mixer. The second local oscillation circuit oscillates a second local oscillation signal using the SAW oscillator. The frequency converter converts a frequency of the second local oscillation signal to generate a first local oscillation signal. The first mixer mixes the first local oscillation signal with an input signal to output a composite signal to the SAW filter. The second mixer mixes an output from the SAW filter with the second local oscillation signal to output a frequency conversion signal.

Abstract: The invention relates to an adjustable filter comprising means for analysing the received signal which identifies the type of interference signal present from a predetermined set of interference signal types and an adaptive filter responsive to a control signal produced by the means for analysing the received signal dependent on the type of the interference signal detected.

Abstract: A method of controlling the time constant of a filter for use in a radio receiver which receives a signal, transmitted from a transmitting station at a predetermined period, intermittently at the predetermined period and demodulates and delivers the received signal, a filter circuit having the time constant control function based on the method, and a radio receiver having the filter circuit. Preferably, the filter has its time constant switchable stepwise and specifically, parallel connection of capacitors or shortcircuiting of resistors is controlled by turning on/off switches.

Abstract: A radio-frequency detection apparatus including a signal input for providing an input signal and a phase shifter having a first connection and a second connection. The phase shifter includes a SAW device having a first electrical connection and a second electrical connection, wherein the SAW first electrical connection is coupled to the phase shifter first connection and the SAW second electrical connection is coupled to the phase shifter second connection. The radio-frequency detection apparatus also includes a multiplier having a multiplier first input connection, a multiplier second input connection and at least one multiplier output connection, the multiplier first input connection being coupled to the signal input and the phase shifter first connection and the multiplier second input connection being coupled to the phase shifter second connection. The phase shifter introduces approximately a 90 degree phase shift into the input signal at approximately the frequency of minimum insertion loss.

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 narrow-banded with respect to the channel bandwidth, is controlled in dependence on the receiving conditions. 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 said 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 circuits providing signals characterizing receiving and interference states.

Abstract: A bandpass filter, having an input port and an output port, comprises a first microstrip split-ring resonator coupled to input port, and a second microstrip split-ring resonator coupled to the first microstrip split-ring resonator, and coupled to the output port. A lumped or distributed capacitance is disposed between the first microstrip split-ring resonator and the second microstrip split-ring resonator.

Abstract: A filter (13) for providing temperature compensation for the quality factor thereof comprises transconductance amplifiers (23 and 24) in a gyrator configuration coupled between an input node (21) and an output node (22). A parallel capacitor (25) is coupled between the input node (21) and a supply voltage, and a parallel resistor (26) is coupled between the input node (21) and the supply voltage. A series capacitor (27) is coupled to the output node (22), and a series resistor (28) is coupled between the second capacitor (27) and the supply voltage.

Abstract: A receiver apparatus having a mixer circuit, an oscillator circuit and a tuner circuit is provided with a trap circuit, interposed between the tuner circuit and the mixer circuit, for removing disturbing mutual modulation waves generated by receiving two or more RF signals. Further, the mixer circuit employs a double balanced mixer structure to offset two or more disturbing mutual modulation waves.

Abstract: A band switching filter circuit includes a first filter for filtering an input signal with predetermined characteristics to output a first filtered signal, and a second filter for filtering the first filtered signal output from the first filter with frequency characteristics of a band narrower than that of the frequency characteristics of the first filter to output a second filtered signal. A switching circuit selects the first filtered signal output from the first filter or the second filtered signal output from the second filter in accordance with the level of an input control signal.

Abstract: Networks which remove the jamming signal from the television signal supplied to subscribers for a premium T.V. channel in a cable (CATV) or other subscription television system utilizes surface accoustic wave (SAW) devices arranged to provide a broadband all pass response across the entire band covered by all of the transmitted television channels except for a notch at the frequency of the jamming signal. The narrow band response of the filter in the premium channel is such that the notch presents insertion loss at the jamming signal frequency and over a frequency range to accommodate shifts in the frequency response of the SAW devices with respect to the frequency of jamming signal, which insertion loss is about 100 times the insertion loss at the picture carrier frequency of the television signal, even though the picture carrier and the jamming signal frequency may be within about 200 KHz apart from each other.

Abstract: A bandpass filter is disclosed which may be used in a superheterodyne receiver in front of the first mixer. The bandpass filter provides a narrow front end filter which is tuned automatically as the local oscillator frequency is changed. In the present exemplary embodiment, a series tuned reflective notch filter is coupled to a node of a balanced resistive bridge in such a manner that the tuned circuit presents a short circuit to the node at the filter's resonant frequency to thereby assure a maximum transfer of signal from the input to the output of the circuit at a desired frequency. At all other frequencies, the series tuned reflective notch filter will present essentially an open circuit across the node of the resistive bridge so that the node is balanced and no transmission occurs. The inclusion of the series reflective notch filter thereby produces a bandpass characteristic from the circuit input to output.

Abstract: A stripline split-ring resonator bandpass filter comprises first and second conducting layers and first and second substrates connected to each other between the conducting layers. A first stripline ring resonator is located on the top side of the second nonconducting substrate and is coupled to the input port of the BPF. The first stripline ring resonator has a gap located therein. A second stripline ring resonator is also located on the top side of the second nonconducting substrate between the first stripline ring resonator and the output port of the BPF. The second stripline ring resonator has a gap located therein. The first substrate has at least two slots therein to allow lumped capacitors to be placed in the gaps in the first and second ring resonators.

Abstract: The RF data communication band pass filter is a fixed device that filters both RF multi-level data signals and binary-level data signals. The RF data communication band pass filter comprises a low pass filtering means having a corner frequency of approximately 2900 Hertz and as high pass filtering means of approximately 340 Hertz. By using precision components the overall group delay envelope is such that both multi-level RF data signals and binary-level RF data signals are adequately filtered without substantial harmonic distortion or spectral distortion. In addition, the communication band pass filter meets the strictest of international RF data communication requirements.

Abstract: An SCA receiver is provided which has a close to ideal passband characteristic which greatly improves frequency response to produce a brighter sound due to the use of ceramic resonator elements. The use of ceramic resonator elements and a superheterodyne approach also provides a receiver which can be rapidly aligned and which has improved noise protection, lower distortion, increased stability, less residual subcarrier in the audio, and more consistent performance from one unit to the next. In one embodiment the superheterodynes circuit operates at 455 kHz which up-converts the usual 67 kHz signal by mixing it with the output of a ceramic resonator controlled local oscillator/mixer. The ceramic resonator and ceramic filter along with the local oscillator/mixer I.C. provides low group delay, improved impulse noise rejection, while most importantly achieving at least an order of magnitude better audio response over the signal bandwidth.

Abstract: The present application relates to an active bandpass amplifier comprising a single stage operational amplifier, a bridged "T" network single frequency elimination filter in the negative feedback path of the amplifier and a phase shift correcting capacitor associated with the bridged "T" network single frequency elimination filter to effect a phase shift sufficient to maintain an appropriate feedback such that the amplifier is stable. The bridged "T" network single frequency elimination filter in conjunction with the circuit capacities and phase shifts in the integrated circuits introduces a phase shift which would result in the amplifier oscillating when the network is placed in the feedback path and the corrective capacitor effects a corrective phase shift to render the amplifier stable.

Abstract: A zero-IF radio receiver circuit comprises an input filter (3), quadrature mixers (9,10), d.c.-blocking capacitors (24,26) and a demodulator (22). The circuit is partly integrated on a semiconductor chip and an inductive component of the input filter comprises one or more of the chip bond-wires. In order to compensate for the inevitable variation of the inductance of these bond-wires from circuit to circuit part of the signal from the local oscillator (12) is added to the input signal before its application to the input filter and the d.c. component of the resulting output from one mixer (10), which component is representative of the phase shift of the local oscillator signal produced by the input filter and hence of any tuning error of this filter, is applied to a tuning control input (30) of the filter to reduce the error. Alternatively the tuning control signal may be adjusted to maximize the sum of the squares of the d.c.

Abstract: A modem for transmitting and receiving digital information includes an oscillator, a switch connected to both the oscillator and to a data input for switchably controlling the oscillator to impress data on a transmission channel, and a receiver also connected to the transmission channel for receiving data thereon to demodulate the data and supply it to a processor.

Abstract: A complex circuit component for a video signal circuit in a television receiver set has a single substrate, on which a first ceramic trap for removing speech carrier wave together with an inductor for that trap, a second trap for removing color subcarrier wave, and a delay circuit coupled with output of said second trap are mounted. The capacitors for those circuits are implemented by a pair of conductive patterns deposited on front surface and rear surface of the substrate. The capacitor for said first ceramic trap is subject to trimming so that the characteristics of the trap is adjustable.

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 split band filtering scheme to reduce adjacent band interference in a communications network, such as a cellular mobile radio system, is disclosed. A repeater, interposed between a base or cell site and a mobile/portable radio, includes a down converter for converting a system operating frequency to a lower frequency signal. The lower frequency signal represents a communications band. The signal is presented to a split band filter having a narrow passband with steep skirts. The processed signal is coupled to an up converter where it is restored to the system operating frequency. In this way, the passband of the repeater is restricted to that of the desired communications band and adjacent band interference is reduced or eliminated.

Abstract: A circuit arrangement of input stages for a television tuner for the UHF, VHF and hyperband frequency bands in a continuous frequency range having primary bandpass filters for the UHF and VHF bands arranged in parallel, and connected to a signal input aerial (7). The input of the VHF primary bandpass filter is coupled to at least one grounded first inductance (27), series-arranged second and third inductances (29 and 31) between the output and the first inductance (27) and a grounded variable capacitor (33) arranged at the output and a first switch (35) which shunts the second inductance (29) and switches between the BI and the BIII ranges of the VHF band.

Abstract: Scrambling and descrambling systems utilizing jamming signals provide improved pictures with minimal distortion due to ghosts and artifacts. The television signal is combined with a jamming signal or signals located preferably in the vestigial sideband (VSB) of the modulated picture carrier and at about a null in the spectrum of the modulation of the picture carrier by the horizontal sync. The jamming signal or signals also preferably are placed between the harmonic components of the horizontal sync which define the horizontal sync spectrum and at frequencies which comply with governmental regulations respecting frequency locations of strong signals of CATV purposes. The jamming signals are generated by phase locking to the horizontal sync signals of the television signals or to a submultiple of the horizontal sync frequency.

Abstract: The invention relates to a circuit arrangement for a tuner, particularly a television tuner, for a change over switching between two frequency bands with the aid of a switching diode, said frequency bands, particularly the VHF band and the hyperband, being filtered out by means of bandpass filters (1,7). The bandpass filters have at their inputs and outputs capacitance diodes for the purpose of tuning. The filtered signals are applied to a common tunable circuit (15) on the secondary side of the bandpass filters. The bandpass filter for the hyperband is constructed and dimensioned such that the signal is switched through by means of a switching diode (83) arranged at the low end of the bandpass filter (1). When this diode (83) is conducting a smaller output reactance, whereas in the case of a blocking switching diode (83), this bandpass filter (1) cuts off the signal and has a larger output reactance.

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.