Abstract: A method of reducing noise and ingress in cable return paths is disclosed in which the return frequency spectrum is divided into two regions; one frequency region being for transmissions from in-home devices such as television settops and personal computers, and another frequency region being for transmissions from communications devices called coaxial termination units located between the drop cable and the home coaxial wiring. By locating blocking filters between the drop cable and home coaxial wiring, undesirable signals emanating in the home in the second part of the return spectrum are prevented from entering the cable return system. The location of the blocking filter reduces the noise in the second part of the return spectrum substantially and allows the establishment of reliable telecommunications services on the cable return in such second part of the return spectrum.

Abstract: A phasing receiver includes a quadrature mixing arrangement for frequency converting an input or high IF information signal to a pair of quadrature related low IF signals. The low IF signals are applied to a polyphase filter which functions as a low pass and adjacent channel rejection filter. One or more elements effecting a fine adjustment of relative phase away from quadrature and/or relative amplitude away from equality of the low IF signals are incorporated in information or oscillator signal paths in or about the mixing arrangement or a superhet stage preceding the quadrature mixing arrangement. These elements effect a predistortion of relative phase and/or relative amplitude of the low IF signals in order to compensate for mismatches in an input stage of the filter, and thereby improve image rejection by the filter.

Abstract: The invention provides a frequency converter for a cable television transmitter, which executes frequency conversion with one frequency mixer to simplify the total configuration, to prevent deterioration of the carrier vs. noise ratio, and to effectively remove spurious frequency components. The frequency converter of the invention includes a frequency conversion unit that executes frequency mixing of an intermediate frequency signal and a local oscillator signal to convert the intermediate frequency signal into a high frequency signal corresponding to a transmission channel, and plural stage variable tuning filters connected in cascade to the output of the frequency conversion unit, which are each individually tuned to the high frequency signal corresponding to the transmission channel.

Abstract: A signal having a substantially uniform spectral distribution, e.g., a flat noise signal such as a signal ground, is provided at the input of a bandpass filter such as an IF filter of a receiver circuit, to thereby produce an output signal at the output of the bandpass filter. The output signal is processed in a limiter to produce a limited signal. An average frequency of the limited signal is determined, and the bandpass filter is adjusted based on the determined average frequency. According to one embodiment of the present invention, the bandpass filter comprises a Gm-C filter having a transconductance, and the filter is adjusted by adjusting the transconductance of the Gm-C filter based on the determined average frequency. According to another aspect of the present invention, a desired center frequency for the bandpass filter is identified. A resolution and a desired confidence interval are also identified.

Abstract: A hands-free cellular telephone base includes a privacy switch unit having a contact switch and a spring-biased switch actuator. The contact switch is mounted in a housing and is operable to control operation of a control circuit unit between a privacy mode and a broadcast mode. The switch actuator is mounted movably on the housing and is movable from a normal position, where the switch actuator does not actuate the contact switch for operation in the privacy mode, and a pressed position, where the switch actuator actuates the contact switch for operation in the broadcast mode. A magnet member is disposed in the housing such that, when an earphone is disposed adjacent to the switch actuator, the magnet member will attract with the earphone, thereby forcing the switch actuator to the pressed position against biasing action of the spring.

Abstract: A variation in tuning frequency of an RF tuning circuit due to temperature changes in a radio receiver is prevented. A tuning frequency of an RF tuning circuit results from a coil (L) and a varicap diode that constitute the RF tuning circuit. A capacitance of the diode is corrected on the basis of a received frequency of a desired station and characteristics of the diode so that the tuning frequency matches the desired station. Thereafter, a temperature is detected by a temperature detection circuit. If a detected temperature T is within 0° C. to 50° C., the tuning frequency of the RF tuning circuit is maintained without change. If the detected temperature T is below 0° C. or higher than 50° C., the tuning frequency is fine adjusted to become lower or higher, respectively.

Abstract: A signal having a substantially uniform spectral distribution, e.g., a flat noise signal such as a signal ground, is provided at the input of a bandpass filter such as an IF filter of a receiver circuit, to thereby produce an output signal at the output of the bandpass filter. The output signal is processed in a limiter to produce a limited signal. An average frequency of the limited signal is determined, and the bandpass filter is adjusted based on the determined average frequency. According to one embodiment of the present invention, the bandpass filter comprises a Gm-C filter having a transconductance, and the filter is adjusted by adjusting the transconductance of the Gm-C filter based on the determined average frequency. According to another aspect of the present invention, a desired center frequency for the bandpass filter is identified. A resolution and a desired confidence interval are also identified.

Abstract: An improved wrist-carried radiotelephone includes a first housing including a microphone, a display and a radio transceiver. A second housing includes a latch, a user interface, a speaker, and a removable battery. A flexible wristband has a first portion including an antenna extending downwardly and a latch clip at one end thereof operable to be received in the latch of the second housing. A second portion of the wristband includes electrical connections to connect the circuits of the first and second housing. The wristband includes support members to maintain the wrist-carrier radiotelephone in a predetermined configuration when the first portion of the wristband is unlatched from the second housing such that the speaker and microphone of the radiotelephone are at an optimum orientation in relation to a user's ear and mouth.

Abstract: A programmable dynamic range receiver which provides the requisite level of performance at reduced power consumption. The .SIGMA..DELTA. ADC within the receiver is designed with one or more loops. Each loop provides a predetermined dynamic range performance. The loops can be enabled or disabled based on the required dynamic range and a set of dynamic range thresholds. The .SIGMA..DELTA. ADC is also designed with adjustable bias current. The dynamic range of the .SIGMA..DELTA. ADC varies approximately proportional to the bias current. By adjusting the bias current, the required dynamic range can be provided by the .SIGMA..DELTA. ADC with minimal power consumption. A reference voltage of the .SIGMA..DELTA. ADC can be descreased when high dynamic range is not required, thereby allowing for less bias current in the .SIGMA..DELTA. ADC and supporting circuitry. The dynamic range of the .SIGMA..DELTA. ADC is a also function of the oversampling ratio which is proportional to the sampling frequency.

Abstract: A radiotelephone unit for conducting time division mutiplex receiving includes a two intermediate-frequency filters provided with the same performance, and switches for switching alternately the two intermediate-frequency filters every time when a receive slot is changed. First and third receive slots are associated with one IF filter and second and fourth receive slots are associated with the other IF filter.

Abstract: A tunable filter (400) provides dual injection mode operation over a continuously tunable frequency range (500). A combination of mirrored series resonant circuits (432, 446) tuned through varactors (434, 448) allows the frequency response to shift. The use of a series capacitor and shunted inductor (430, 428), (444, 442) mirrored onto each series resonator (432, 446) provides both high-side and low-side injection protection.

Abstract: A first mixer (306) shifts a first end (208) of a desired signal frequency bandwidth (206) of a desired signal (202) to an edge (508) of a first filter frequency bandwidth (502) of a first filter (312), wherein the first filter frequency bandwidth (502) is greater than the desired signal frequency bandwidth (206). Signals within a first undesired frequency spectrum (504) are attenuated by the first filter (314). A second mixer (316) shifts a second end (210) of the desired signal frequency bandwidth (206) to an edge (608) of a second filter frequency bandwidth (602) of a second filter (320) to receive the desired signal (202).

Abstract: To achieve a high passband attenuation, a switchable bandpass filter for a multiband tuner, includes at least a capacitance diode for frequency-tuning of at least a resonant circuit of the bandpass filter, and a switching diode arranged at the input and the output, this switching diode being switchable to either the blocked state or to the conducting state by DC voltages. The capacitance diode is additionally usable for blocking the bandpass filters and is integrated in the resonant circuit of the bandpass filter in such a way that, in dependence upon a switching potential, the capacitance diode couples the resonant.

Abstract: A receiver includes at least two intermediate frequency (IF) filters, with the first IF filter and a second filter having a narrower bandwidth than the first bandwidth. The receiver also includes a switch operable to select between the IF filters. In use, the receiver measures the signal strength of adjacent channels to the signal strength of a desired channel and switches to the second IF filter with a narrower bandwidth when a ratio of the signal strength of the channel and the signal strength of adjacent channels is less than a predetermined threshold. The predetermined threshold is determined based on considerations of range of detection and adjacent channel interference. The bandwidth of the filters in the receiver is also designed to optimize performance in consideration of both range of detection and adjacent channel interference.

Abstract: A radio communication apparatus is designed for at least first and second radio communication formats which prescribe first and second desired IF pass bandwidths respectively. The first desired IF pass bandwidth is greater than the second desired IF pass bandwidth. The radio communication apparatus includes an IF band-pass filter processing a first IF signal into a second IF signal and having a predetermined pass bandwidth corresponding to the first desired IF pass bandwidth. A demodulator recovers a first baseband signal from the second IF signal generated by the IF band-pass filter. A baseband filter processes the first baseband signal generated by the demodulator into a second baseband signal. The first baseband signal generated by the demodulator is selected as a final output signal when the first IF signal is of the first radio communication format.

Abstract: This separating device is provided with a transmitting filter and a receiving filter. Each of the transmitting and receiving filters comprises a variable capacity diode and a resonant element, and compose a band elimination filter. Each of the elimination bands of the transmitting and receiving filters can be adjusted by changing the capacity value of each variable capacity diode. The elimination band of the transmitting filter is adjusted so as to coincide with the receiving frequency of the communication channel currently used. The elimination band of the receiving filter is adjusted so as to coincide with the transmitting frequency of the communication channel currently used.

Abstract: A method and apparatus for tuning an analog filter that is embodied in a larger circuit in which the analog input signal to the filter is, at some point prior to the filter, in digital form. The digital version of the input signal to the filter is stored in memory. The output signal from the filter corresponding to the stored input signal is digitized and compared to the stored digital input signal to the filter. Based on the known input signal and the known desired frequency characteristics of the filter, the desired output signal is a known quantity. If the actual output signal differs from the expected output signal, the filter is tuned accordingly. The process may be performed continually on all input data or on discrete sections of the input data.

Abstract: For eliminating the emphasis given an audio signal in the transmitter, an audio signal processor of an audio device (e.g., a car radio) contains a low-pass filter. In order to attenuate the spurious higher-frequency signal fractions in case of poor reception and accordingly low received field strength, the cutoff frequency of the low-pass filter is shifted in the direction of lower frequencies in accordance with a received field strength signal when the field strength becomes lower. In order to avoid external adjusting components and save pins on the IC chip, the field strength signal is supplied to an analog-to-digital converter and the latter supplies a digital signal to a low-pass filter whose cutoff frequency is variable. For this purpose the low-pass filter contains a number of integrated components one of which is connected or disconnected by a digit place of the digital signal in each case.

Abstract: A radio communication apparatus uses an intermediate frequency section to convert a signal from a receiver into an intermediate frequency signal. The intermediate frequency signal is filtered in a filter section, and then demodulated. Matching circuits with variable circuit constants connect the filter section with the intermediate frequency section and the demodulator. A control section supplies a transmitter with an input signal which is then transmitted to the receiver, converted to an intermediate frequency, filtered, and demodulated. The control section adjusts the variable circuit constants in accordance with the input signal and the demodulated signal. Thus, inappropriate circuit constants are adjusted so that the radio apparatus has a high receiving sensitivity without a mismatch.

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 variable-gain amplifier circuit has an offset correcting function by which the fluctuation of offset due to the switching of a gain is decreased. In an offset detection mode, an input offset voltage of the variable-gain amplifier circuit is inputted to an offset retaining section, and in a signal amplifying mode, the offset is corrected by subtracting the output of the offset retaining section from an input signal by means of an input section of the variable-gain amplifier circuit. In addition, the variable-gain amplifier circuit can be applied to a radio receiver. The offset produced in a baseband section of a receiver is corrected by the offset correcting function of the variable-gain amplifier circuit, so as to prevent the quality of communication from being deteriorated.

Abstract: A method and apparatus for automatic tuning calibration of electronically tuned filters which comprises a programmable frequency generator for producing a calibration frequency signal, a filter for filtering the calibration frequency signal, a detector for producing a detector voltage, a processor for programming the frequency generator to specific test frequencies and for producing a stepped filter tuning voltage and storing the detector voltage in response to the stepped filter tuning voltage, and a converter for digital-to-analog conversion of the stepped filter tuning voltage. Calibration frequency signal versus tuning voltage responses are stored for a number of calibration iterations within the usable range of the filter and the resulting table can be used to determine the correct tuning voltage for the filter when operating at any frequency within the usable filter range.

Abstract: A mobile telephone receiver, utilized in a cellular communications system, is provided with a group of IF bandpass filters which are arranged in parallel and which respectively have different passbands with each other. The IF filter group allows an incoming IF signal to be filtered out using one of the IF bandpass filters. A signal contamination determiner is operatively coupled to the IF filter group and detemines a degree of signal contamination by examining a signal which has passed through the IF. bandpass filter selected for filtering the incoming IF signal. The selector changes the selection of the IF bandpass filters according to the degree of signal contamination.

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: A radio receiver is disclosed for demodulating both wideband and narrowband frequency-modulated signals. The radio receiver improves the capacity of a system by reducing the bandwidth occupancy of analog frequency modulation systems. The radio receiver comprises a superheterodyne frequency device which converts the received frequency-modulated signal to a fixed intermediate frequency signal. A filter then filters the intermediate frequency signal with a first filter bandwidth adapted to a wideband frequency-modulated signal. The filtered wideband frequency-modulated signal is demodulated in a demodulator using a frequency discriminator. The intermediate frequency signal is then filtered using a second and third filter bandwidth adapted to a narrowband frequency-modulated signal. Finally, the further-filtered intermediate frequency signal is demodulated using a frequency discriminator.

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 synchronous tracking filter circuit for use in a broadcast satellite tuner that comprises four varactors and a strip-shaped inductor plate or pcb-printed strip line which produces a resonant frequency. The circuit is used in a doubly tuned resonant circuit to incorporate the tracking with the frequency changes of a voltage controlled oscillator (VCO) synchronously. The circuit can also control the image interference. This type of design is applicable in the tuner of an indoor broadcast satellite receiver unit to act as the synchronous tracking filter of input frequencies.

Abstract: An FM receiver having an RF section, a first tunable mixer stage for the frequency conversion of a desired RF FM reception signal into a first intermediate frequency signal, an IF device and an FM demodulator. In order to enhance the integration of the apparatus, while maintaining a signal processing ability which is free from distortion, the FM receiver includes circuitry incorporated in the signal path for converting a single-phase signal into a pair of signals in mutual phase quadrature. The pair of phase-quadrature signals is applied to in-phase and quadrature signal paths of the IF device. The IF device having a polyphase IF filter incorporated in the in-phase and quadrature signal paths and has a bandpass characteristic which is symmetrical around its resonance frequency. The polyphase IF filter is coupled to the FM demodulator.

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 device for filtering wide-band signals at radio frequencies is usable either in a base station cellular telephony system or separately. The wide-band signal occupies a total frequency band comprising frequency bands allocated to that signal and a central frequency band extraneous to that wide-band signal. Within the device, the wide-band signal is mixed with a heterodyne wave to translate the signal from RF to IF. The signal at IF is then filtered by two surface acoustic wave (SAW) band-pass filters which have respective pass bands which correspond at IF to the allocated frequency bands of the wide-band signal, and which the SAW filters have the filtering effect of passing with low attenuation signals in those allocated bands while substantially attenuating signals and/or noise in the central extraneous frequency band between those allocated bands.

Abstract: A radio receiver has a frequency down conversion stage including a first passive filter tuned to a lower frequency. An amplifier functioning as a voltage-to-current converter includes a resistor (60) which can be shunted by a second passive filter in response to actuation of symmetrically arranged switching devices. When the second passive filter shunts the resistor, the overall pass band is raised to a higher frequency. Additionally, the amplifier has a lower noise figure when the second passive filter shunts the transconductor.

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 CW (Continuous Wave) radio frequency signal converted to an IF (Intermediate Frequency) signal is mixed with a local oscillator signal by an IF mixer, and the obtained signal is converted to a digital signal by an ADC (Analog-to-Digital Converter). A digital bandpass filter passes only the target component in the output of the ADC. The passed IF signal is demodulated by a digital demodulator, and the demodulated signal is converted to an analog signal before being output as a sound. When pitch control to increase the reception pitch by .DELTA.f is instructed, an MPU (Microprocessor Unit) alters the frequency of the local oscillator signal by .DELTA.f as well as the center frequency of the digital bandpass filter by .DELTA.f, so that the center frequency of the input signal to a narrow-band filter coincides with the center frequency of the digital bandpass filter.

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: The present invention relates to a method of tuning a radio receiver to a desired frequency. The frequency of each tuning circuit in the radio receiver is controlled by controlling the capacitance diodes of the tuning circuits. The control is accomplished with an individual DA converter arranged for each tuning circuit with which the frequency of the tuning circuit associated therewith can be controlled independently of the other tuning circuits. The optimal control values of each DA converter is defined at least in two points of the frequency range of the radio receiver. These control values are stored in a memory provided in the radio receiver. On the basis of the stored control values the control values for the entire frequency range are calculated for each control means.

Abstract: A tunable filter (25) is described for use in loop control circuits. The filter (25) has a time constant which is determined by a resistor (40) and a capacitor. The capacitor is simulated by the series combination of an impedance converter (41) and a variable resistor, such as a field effect transistor (42). The resistance of the transistor (42) is determined by a control signal present on a control line (32) and the impedance converter (41) converts the resistance into an equivalent capacitive reactance. Therefore, the control signal on the control line (32) effectively controls the capacitance present at a node (43) and, in conjunction with the resistor (40), determines the time constant, and therefore the response time and bandwidth, of the filter (25). Multiple pole, lowpass, bandpass, highpass, and bandstop filters can be constructed. The impedance converter (41) uses a very small capacitor to simulate a large capacitance value at the node (43).

Abstract: The invention provides a filter circuit for use in a double-conversion TV tuner exhibiting low diode insertion loss, in which intermodulation distortion does not occur even when an incoming signal has a large amplitude. In the filter circuit according to one preferred embodiment of the invention, there are provided three bandpass filters (BPFs) which allow corresponding RF signals in different frequency bands to pass through them, and six variable attenuation diodes whose impedance is controlled by an AGC voltage applied to an AGC terminal (16). There are also provided switching diodes (20) disposed between an input terminal (1) and the inputs of three BPFs so that the switching diodes (20) select exclusively one of three BPFs so as to apply an RF signal received at the input terminal (1) only to the selected BPF (it will be assumed hereinbelow that the BPF (21) is selected).

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: A method for tuning and aligning an electronically tuned FM broadcast receiver is described. The system described compensates for the mismatch of component values between the antenna and RF amplifier tuned circuits, and the IF offset between the local oscillator frequency and the center frequencies of the antenna and RF resonant circuits by developing independent tuning signals for the circuits. The system also provides temperature compensation, and can be aligned without mechanically adjusting inductors and/or capacitors in the tuned circuits.

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: 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 power divider couples a received signal to a pair of signal channels. The first channel includes a pulse signal processor coupled to the power divider through a band reject filter. The second channel includes a continuous wave signal detector and processor coupled to the power divider through a bandpass filter. The bandpass and band reject filters are responsive to a control signal for tuning the center frequencies of the respective pass band and reject band to a frequency within a predetermined range of frequencies. The continuous wave signal detector and processor determines the frequency of a detected continuous wave signal using the first channel, and tunes, by producing the above-mentioned control signal, the center frequencies of the bandpass and band reject filters to the frequency of the detected continuous wave signal. The band reject filter rejects the continuous wave signal in the first channel.

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: 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: 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: A variable frequency RF passband filter is aligned or calibrated to maximize the sensitivity of a radio receiver using reference frequencies obtained using a fixed frequency oscillator present in a different band tuning section of a multiband receiver. The intermediate frequencies of the various band sections of the multiband receiver are selected whereby a fixed frequency source in one band corresponds to an intermediate frequency employed in the band for which the tunable RF filter is being aligned.

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: Interference detection and reduction is disclosed in which an interference carrier is reduced by processing a signal of an input frequency to a demodulator such as a PSK signal appended with bit sequence for carrier recovery and bit timing recovery for use in the TDMA system, for example, a signal of the intermediate frequency (IF) band of a 140 MHz center frequency, so that the attenuation of a band-elimination filter is limited to a value smaller than a certain one, or for the frequency bands in which spectra are produced by the bit sequence, the IF signal is combined with the band-elimination filter output via a narrow band-pass filter to control the attenuation in each of these frequency bands to a value smaller than a certain one, thereby preventing the signal quality of the TDMA signal from being degraded by the insertion of the band-elimination filter.

Abstract: An FM subcarrier receiver of the type useful for detection of a relatively high frequency subcarrier signal transmitted on an FM carrier which includes baseband and relatively high frequency signals is disclosed. It comprises radio frequency circuitry for providing a radio frequency signal having frequency modulated baseband and subcarrier components. High pass filter circuitry receives the output of the radio frequency circuitry. A tuned circuit receives the output of the high pass filter. It comprises a first inductor and a first capacitor tuned substantially to the frequency of the subcarrier which one wishes to detect. A second tuned circuit is tuned to the subcarrier which one wishes to detect. The second tuned circuit comprises a second inductor and a second capacitor. The first and second inductors comprise ferrite cores and are positioned with respect to each other to allow magnetic coupling therebetween.