Abstract: A multiband receiver and associated method are provided for simultaneous reception of a number of RF signals with partially different carrier frequencies. An RF/IF converter is provided with a number of local oscillators corresponding to a number of RF signals in order to produce L0 in phase components corresponding to the carrier frequencies and quadrature components; in addition to an in-phase mixer and a quadrature mixer for mixing the respective L0 in-phase and quadrature components with the RF signals in order to produce intermediate frequency signals with IF in-phse components and IF quadrature components. A complex fiber carries out complex filtering on the basis of the intermediate frequency signals in order to suppress reflected intermediate frequency signals.

Abstract: A mixer circuit can suppress image interfering signals and interfering signals related to higher harmonic component of an oscillator. Using the mixer circuit, it is possible to provide a high-frequency signal receiver which maintains good signal receiving condition. This mixer circuit comprises a plurality of mixers, oscillators, a plurality of oscillator phase shifters which serve to phase-shift the output of the oscillators and supply the output to the mixers, and a plurality of intermediate frequency phase shifters which serve to phase-shift the output of the mixers. The high-frequency signal receiver comprises at least a pre-filter and the mixer circuit.

Abstract: A radio transceiver comprises a reception path, a transmission path, and a frequency generator with a programmable phase lock loop. The reception path, the transmission path, and the frequency generator share a maximum amount of common circuitry to facilitate implementation of the entire radio transceiver on a single integrated circuit. The reception path includes an amplifier and a quadrature mixer for producing low intermediate frequency signals. The transmission path can be controlled by either a modulated voltage controlled transmitter or an in-phase and quadrature modulator transmitter.

Abstract: A received wireless signal contains a plurality of path components, each having a phase indeterminate data stream derived from an original data stream. The receiver splits the received signal into N signal copies for N raking channels, which correlate each of the N signal copies with N locally generated signals, respectively, to generate N correlated signals. Each of the N correlated signals carries an estimated phase indeterminate data stream. The raking channels then synchronize each of the correlated signals to a system clock in phase and frequency to generate N synchronized signals. The N raking channels then align the N synchronized signals to generate N aligned signals, each of which carries an aligned path data stream that is normalized in time with respect to the other aligned signals. Finally the receiver combines the aligned signals to produce an estimated original data stream.

Abstract: A receiver for rejecting an image signal is provided that does not require a phase-shifter and that requires less mixers than prior receivers. Thus, the phase imbalances and gain mismatches imparted by phase shifters are avoided, and harmonics due to non-liner effects in the mixers are reduced.

Abstract: A radio transmitter system designed using an FSK modulator with IQ up-mixers and sinewave coded digital-to-analog converters (DACs). The radio transmitter system may include a frequency shift keying (FSK) coding logic circuit coupled to the inputs of an IQ modulation and image reject up-mixer through a respective DAC and a respective low pass filter (LPF) for each the I and the Q channels. The FSK modulation scheme may employ sine and cosine signals for the I and Q channels, respectively, where the sine and cosine waves are directly coded into the DACs. The coded levels required by the DACs may be generated using current sources and may be Gray-coded. The output of the IQ modulation and image reject up-mixer may be connected to a power amplifier, which may be used to transmit the modulated RF signal via a loop antenna.

Abstract: Techniques to correct for phase and amplitude mismatches in a radio device in order to maintain channel symmetry when communicating with another device using MIMO radio communication techniques. Correction for the amplitude and phase mismatches among the plurality of transmitters and plurality of receivers of a device may be made at baseband using digital logic (such as in the modem) in the receiver path, the transmitter path or both paths of that device. In a device, amplitude and phase offsets are determined among the plurality of radio transmitter and radio receiver paths by measuring phase and amplitude responses when supplying a signal to a transmitter in a first antenna path of the device and coupling the radio signal from a first antenna to a second antenna path of that device where the signal is downconverted by a receiver associated with the second antenna path, and similarly coupling a signal from the second antenna path to the first antenna path.

Abstract: The present invention relates to an apparatus for cancellation of electromagnetic interferences (n), including means (3) for dividing a reference signal (sc) into a first and second signal (scl, scQ) having different phases, tow multipliers (4, 5) for each multiplying a weight coefficient to one of the phase displaced signals (scl, scQ) each and for outputting a multiplied signal each, and adder (6) for adding the two multiplied signals and for outputting a corrected reference signal (sn), and a subtracter (7) for subtracting the corrected reference signal (sn), from an input signal (sd) and for outputting an error signal (se). According to the invention different weight coefficients (l(f), Q(f)) are used for different frequencies or frequency bands (f) of the interference (n).

Abstract: An image rejection mixer of reduced power dissipation includes a signal distributor supplied with local signals having a phase difference to distribute the local signals, a first and a second signal mixer for mixing the distributed local signals and RF signals having a phase difference and outputting respective IF current signals, a phase shifter for shifting in phase the respective mixed IF current signals so as to provide them with a relative phase difference of 90 degrees, and a signal adder for adding the respective phase shifted intermediate frequency current signals. The shifter shifts the phases of the respective IF current signals outputted from the first and the second signal mixers.

Abstract: Methods of improving a signal to noise ratio using synchronous rejection are enclosed. Also disclosed are various synchronous rejection systems. In one method of synchronous rejection, the method includes correlating a phase of a reference signal to a phase of the interference signal; collecting a first data set during a first period of time using the reference signal; inverting the reference signal and re-correlating the phase of the reference signal to the phase of the interference signal; collecting a second data set during a second period of time using the inverted reference signal; and integrating the first and the second data set.

Abstract: A direct conversion receiver (DCR) with a pair of quadrature conversion paths. Each of the quadrature conversion paths receives an RF input signal and converts the RF input signal to a digital baseband signal. The quadrature conversion paths each include a mixer mixes the RF input signal with a carrier phase signal. Quadrature baseband signals from the mixer pass through an analog filter which provides a filtered baseband signal. An analog to digital converter (ADC) converts the quadrature baseband component to a digital baseband signal. A 5th order elliptical filter filters the quadrature baseband component. The 5th order elliptical filter may be before or after the ADC. A digital baseband component from the ADC and filtered by the 5th order elliptical filter passes to a phase equalizer which compensates for phase distortion from the analog filter. The quadrature digital baseband outputs from the quadrature conversion paths are passed to a baseband processor.

Abstract: A receiver with reduced near field noise is described. The receiver has a far range receiving section configured to sense a desired signal that includes near field noise. The receiver further includes a near range receiving section configured to sense a near field noise reference signal. An adaptive noise canceller (ANC) of the receiver is configured to detect the magnitude of an error vector from the far range receiving section. The ANC is configured to adjust the phase and gain of the near field noise reference signal in response to the magnitude of the error. Accordingly, the ANC can generate a corrected near field noise reference signal that is added to the desired signal with an adder. The near field noise is canceled by the addition of the corrected near field noise signal. The ANC uses a least mean square technique to determine the amount of correction needed.

Abstract: A signal reception circuit includes a main antenna which receives signals in at least two predetermined reception frequency bands. A sub-antenna receives a signal in one of the reception frequency bands of the main antenna. A filter for interrupting a signal in the same frequency band as the reception frequency band of the sub-antenna is provided on a transmission line of a reception signal of the main antenna. A filter reflection signal in the same frequency band as the reception frequency band of the sub-antenna is induced in the sub-antenna, due to the antenna coupling thereof. The phase of the filter reflection signal is adjusted by a phase shifter between the main antenna and the filter, so that the induced signal of the sub-antenna is in phase with the reception signal of the sub-antenna. As a result, the level of the composed signal of the induced signal and the reception signal and is to be transmitted from the sub-antenna to a signal processing unit is greatly improved.

Abstract: A method and apparatus for minimizing multipath interference for commercial FM signals which use SCA secondary signals in QAM format that includes tracking the time series of phase measurements of a received stereo pilot signal for determining the proper phase reference for demodulation of QAM signals at the center of the time series. Phase measurements of the pilot signal are tracked over a predetermined tracking period. The phase measurement is used to support demodulation of the QAM signal. The SCA secondary signals in QAM format transmitted on commercial FM have minimal multipath interference and Doppler interference by movement of transmitter and receiver (vehicular).

Abstract: A mixer circuit with image frequency rejection comprising a quadrature phase divider (30, 30′) presenting an input connected to the input (Fi) of the mixer circuit and two outputs respectively delivering two signals in phase quadrature which are applied respectively to two simple mixers (31, 32; 31′, 32′), said mixer circuit comprising a quadrature phase and frequency divider (33, 33′) having a frequency division ratio and presenting two inputs respectively connected to the respective outputs of the two simple mixers (31, 32; 31′, 32′) and a first output delivering a first output signal (Fo) of the mixer circuit, which signal is applied to the inputs of the two simple mixers.

Abstract: A transmitter for transmitting a high frequency transmit signal generates a low intermediate frequency quadrature signal, and up-converts the low intermediate frequency quadrature signal to the high frequency transmit signal. The frequency spectrum of the high frequency transmit signal has a transmit band and a sideband corresponding to the transmit band. The transmit band is confined to a total transmit band outside of which severe sideband filtering requirements.apply. Before up-converting, the transmitter provides that the sideband falls at a side of the transmit band such that the sideband falls within the total transmit band.

Abstract: Embodiments of the present invention relate generally to receivers. One embodiment relates to a digital FM receiver having multiple sensors (e.g. antennas). In one embodiment, the digital receiver includes a baseband unit having a channel processing unit. In one embodiment, the channel processing unit is capable of calculating or estimating a phase difference between the incoming signals prior to combining them. One embodiment uses phase estimation method for diversity combining the signals while another embodiment utlizes a hybrid phase lock loop method. Also, some embodiments of the present invention provide for echo-cancelling after diversity combining. An alternate embodiment of the channel processing unit utilizes a space-time unit to diversity combine and provide echo cancelling for the incoming signals.

Abstract: A system is provided that enables real time active phase control at higher RF signal power levels to be achieved by compensation for phase variations due to daily and lifetime fluctuation of equipment temperature, equipment aging effects and path length changes due to redundancy reconfiguration among others. This automated approach achieves the fastest and most accurate phase correction for efficient signal recombining. The system employs an RF signal which is split into parallel paths whose phase is adjusted employing the output of a feedback device and then amplified and sensed to provide the feedback signal and ultimately recombined.

Abstract: The design and performance of an analog cancellation system is presented. The system generates either narrow or wideband nulls in order to minimize the effect of interfering signals on a receiver. A microcontroller directs the detection and classification of the interfering signal relative to frequency, amplitude and modulation, such as pulse-width or continuous wave modulation. A sampled version of the interfering signal at frequency, fi, is phase-inverted, amplified, and vector-summed with the input signal stream to null the interfering signal at fi. The microcontroller also monitors and adjusts the cancellation systems' circuit parameters to minimize any residual interfering signal at fi or respond to changes in the interference. The example system operates from 100-160 MHz, and can generate wideband nulls over a 5MHz bandwidth with a 15dB depth attenuation or narrowband nulls with a Q greater than 200, and with a null depth greater than 30dB.

Abstract: A system and method for a single conversion tuner which generally uses phase shifted in-phase and quadrature-phase signal paths as an image rejection circuit. Through the use of broadband input LNA and mixer circuits, substantially the entire input signal bandwidth may be processed in the tuner. The broadband input LNA may pass the signal through to the mixers, which may split the signal into in-phase and quadrature terms. Then the in-phase term may be shifted by plus 45 degrees and the quadrature may be shifted by minus 45 degrees. When the terms are subsequently summed together, the desired signal components add together, while the undesired image components subtract from each other. In this way the image signal is suppressed, thus generally eliminating the need for a notch filter. A phase error correction feedback loop may be implemented to compensate for errors between the separate circuit paths.

Abstract: A direct conversion receiver is disclosed, in which a DC offset is estimated in two stages. A coarse DC estimation is performed, and the estimate is removed from the received sequence. Then, a coarse synchronization is performed in order to estimate the synchronization position within the burst. Subsequently, a coarse channel estimation and a finer DC estimation are performed simultaneously, and the refined DC estimate is removed. Finally, a refined synchronization and channel estimation are performed, and the refined estimate of the channel is fed to an equaliser, which acts on the received signal, after removal of the refined estimate of the DC component.

Abstract: A noise suppression apparatus for use in a receiver includes an input terminal adapted to receive an inbound signal. A channel splitter is coupled to the input terminal and configured to split the inbound signal into a substantially identical first signal and second signal. A first mixer coupled to the channel splitter and configured to receive the first signal, and a second mixer coupled to the channel splitter and configured to receive the second signal. A first local oscillator is coupled to the first mixer and configured to generate a first LO frequency signal, and a second local oscillator coupled to the second mixer and configured to generate a second LO frequency signal, where the first LO frequency signal and second LO frequency signal differ from one another.

Abstract: A method and apparatus for processing cochannel signals received at a sensor array in a cumulant-based signal processing and separation engine to obtain a desired set of output signals or parameters. For use in a signal recovery system, the output signals are recovered and separated versions of the originally transmitted cochannel signals. An important feature that distinguishes the cumulant-based system from other signal separation and recovery systems is that it generates an estimated generalized steering vector associated with each signal source, and representative of all received coherent signal components attributable to the source. This feature enables the invention to perform well in multipath conditions, by combining all coherent multipath components from the same source. In a receiver/transmitter system, the estimated generalized steering vectors associated with each source are used to generate transmit beamformer weight vectors that permit cochannel transmission to multiple user stations.

Abstract: Phase and amplitude deviations, which are generated, for example, by cables connecting an array antenna of a CDMA base station and the base station, are calibrated in the baseband.

Abstract: Distortion is reduced in a radiocommunications system in which a radio signal is received with a carrier frequency with a group antenna. The group antenna includes at least two receiver channels with an antenna element and components for amplifying and processing the respective signal. A first phase shift by a predetermined value is performed directly after reception of the signal in the respective channel. A second phase shift by a value is performed which corresponds to the first phase shift but in the opposite direction. In this manner, distortion which arises as a result of, for example, non-linearities in an antenna array, is reduced.

Abstract: A system and method for effecting wideband image rejection. In a receiver implementation, the inventive method includes the steps of receiving a first signal in a first frequency band and generating in-phase and quadrature signals therefrom. The phase of the in-phase signal is shifted to provide a second signal and the phase of the quadrature signal is shifted to provide a third signal. A predetermined phase relationship is thereby effected between the second and the third signals. The second and third signals are then summed to provide an output signal which has minimal interference from a mixing signal. In an illustrative receiver application, the phase shifting is achieved via the use of all pass networks. Each of the all pass networks include a differential amplifier having first and second input terminals. The first and the second terminals are connected to a first end of first and second resistive elements, respectively.

Abstract: The invention provides a television reception circuit wherein a front end circuit of a television receiver is integrated and outputting of an image frequency is suppressed. The television signal reception circuit comprises an integrated circuit which in turn includes an automatic gain circuit for controlling a level of an input signal, first and second frequency mixture circuits to which an output of the automatic gain circuit is inputted, a &pgr;/2 phase shifting circuit for supplying local oscillation frequencies having a phase difference of &pgr;/2 from each other to the first and second frequency mixture circuits, first and second &pgr;/4 phase shifting circuits for shifting phases of outputs of the first and second frequency mixture circuits by +&pgr;/4 and −&pgr;/4, respectively, and an addition circuit for adding outputs of the first and second &pgr;/4 phase shifting circuits.

Abstract: If a local oscillation wave of a frequency approximately half the received signal frequency is input to a low noise amplifier 2, a dc offset voltage caused by the nonlinearity of the amplifier is produced, thus degrading reception sensitivity. This problem is resolved by disposing before the low noise amplifier 2 a filter means, such as a bandpass filter 12, band-elimination filter 13, or high pass filter 14, with characteristics for passing the received wave and suppressing a frequency band at approximately half the received wave frequency, thus preventing a radiation wave at substantially the same frequency as the local oscillation wave from being input to the low noise amplifier 2. A filter circuit 15 is also provided in the low noise amplifier 2 as a means for eliminating a radiation wave input to the low noise amplifier 2.

Abstract: An image reject mixer arrangement 1 comprises a transconductor 2, first and second mixer cores 3 and 4, first and second phase shifters 5 and 6 and a summer or combiner 7. The mixer arrangement 1 receives a single-ended RF voltage signal on a terminal 8, a differential local oscillator signal on I-LO terminals indicated at 9 and a 90° phase shifted differential local oscillator signal on Q-LO terminals 10, and provides differential IF output signals on output terminals 11. From the output of the transconductor 2 to the output of the combiner 7, the image reject mixer arrangement 1 carries signals in what can be described as a “current mode”, i.e. it is the current, not the voltage, which conveys the desired signal. In this current mode, it is advantageous to provide each active circuit block with a high output impedance and a low input impedance wherever possible.

Abstract: A direct conversion receiver for receiving a first input signal and directly downconverting it to baseband frequencies. The receiver includes a frequency translator which is responsive to a phase-split input signal having 2n components, wherein n is an integer greater than 1. The phase-split signal has a period T which is about n times the period of the first input. The frequency translator alternates, at a rate of about 2n/T, between switching the first input signal to a first output, and switching the first signal to a second output. A preprocessor is available to improve the switching characteristics of the phase-split input signal.

Abstract: A receiver and an associated method are disclosed for combining signals having substantially different polarizations. The receiver is used with a first antenna which receives first polarized signals and a second antenna which receives second polarized signals, the first polarized signals having a substantially different polarization than the second polarized signals. The receiver includes a phase shifter and a combiner circuit. The phase shifter adjusts the phase of the first polarized signal in response to the phase of the second polarized signal to produce a phase compensated first signal. The combiner circuit sums the second polarized signal and the phase compensated first signal to generate a combined polarization received signal. In this manner, the depolarized signals are phase-aligned with, and then combined with, the polarized signals to provide a strong received signal irrespective of any depolarization of the received signal.

Abstract: In a radio transceiver operating in a time division duplex system, a cancellation use transmission signal which is reverse in phase and equal in amplitude to a leakage transmission signal from an antenna in the signal transmission is supplied to an input port of the receiving amplifier of a receiver connected to an antenna system applied in common to the signal transmission. The transmission signal is fed via a circulator, which separates a transmission and reception path, to the antenna. The leakage transmission signal from the antenna is inputted via the circulator to the receiving amplifier. The cancellation use transmission signal is fed to the receiving amplifier via a second circulator which distributes the transmission signal and cancellation use signal disposed at an output side of the transmitting amplifier.

Abstract: A method and apparatus for determining a delay vector from inputs of in-phase and quadrature phase low pass filters to an output of the demodulator of a dual mixer radio receiver and from such delay measurement computing and providing DC offset correction to said receiver.

Abstract: A weaker signal receiving system inclusive of stronger nearby-sourced interference signal cancellation capability. Stronger interference signal cancellation is accomplished by actively canceling or subtracting from the received signal an intermediate signal in which the weaker signal has been attenuated but the stronger signal remains. Attenuation of the weaker signal in this intermediate signal is accomplished in a feedback loop arrangement by an amplitude-responsive signal processing element embodied from for example a ferrite material such as yttrium iron garnet disposed in a physical wave propagating and wave amplitude sensitive film. The cancellation or subtracting is accomplished using received signals and without need for a direct output sample of the stronger signal at its source. Military aircraft use of the disclosed system in the microwave and other spectral regions with transmission mode as opposed to reflection mode signal amplitude discrimination by the ferrite device is included.

Abstract: The invention relates to a method and apparatus for protecting a transmission path between a base unit and a mobile key unit in an access control system, in particular for motor vehicles. A carrier signal which is modulated with a user signal is transmitted from a transmitting unit to a receiving unit. According to the invention, a separate reference signal, which has a fixed phase angle with respect to the carrier signal, is also transmitted. The phases of the reference signal and of the carrier signal are compared in a test circuit, and an alarm signal is emitted if a phase difference which varies with time is found.

Abstract: A phase compensation circuit, for use with an FM reception system, includes a delay circuit and a control circuit. The delay circuit receives a composite input signal that exhibits a variable phase error and provides a plurality of selectable discrete delays. The control circuit is coupled to the delay circuit and receives a control signal whose value corresponds to the phase error associated with the composite input signal. The control circuit selects one of the plurality of selectable discrete delays responsive to the control signal, which is utilized to delay the composite input signal to provide a phase compensated composite output signal.

Abstract: In a cellular telephone having a receiving circuit of a direct conversion type using an even harmonic orthogonal mixer, high-pass filters for removing a DC offset component are arranged before and after a variable gain amplifier in a base band circuit. The DC offset component occurred in the even harmonic orthogonal mixer is always constant, and the DC offset component occurred in the variable gain amplifier frequently varies so that a cutoff frequency of the front high-pass filter is set to be lower than a cutoff frequency of the rear high-pass filter, and the frequencies are set to achieve a fast transition response.

Abstract: In a demodulator, a local oscillator 7 feeds a local oscillation signal having a frequency of f/n to a phase shifter 8. In the phase shifter 8, all-pass filters 9 and 10 produce two oscillation signals separated in phase by 90/n degrees from each other, which are then fed individually to n-times frequency multiplier 11 and 12. The n-times frequency multipliers 11 and 12 multiply the frequency of those oscillation signals by a factor of n and thereby produce two carriers having a frequency of f and separated in phase by 90 degrees from each other, which are then fed to mixers 2 and 3.

Abstract: A radio frequency identification system includes a transponder and a transponder reader. The transponder, responsive to an interrogation signal continuously transmitted by the transponder reader, generates a transponder signal modulated by an identification signal readable by the transponder reader. The identification signal includes a synchronization portion, a data portion, an output format identification portion, and an error detection portion. The output format identification portion is used by the reader to configure itself for communication with an attached controller. In another aspect of the invention, the transponder reader may be configured to read FSK as well as PSK encoded signals from the transponder.

Abstract: In order to increase accuracy of DC-offset compensation within radio receivers and to ensure that such compensation does not erode the dynamics of the decoders located within the receivers, the present invention separately performs mean value estimation and channel estimation. Additionally, a bias DC offset value caused by the use of a training sequence to perform mean value estimation can be corrected for in the channel estimator and equalizer.

Abstract: A frequency mixing system provides an expanded dynamic range when compared to the dynamic range(s) of an individual mixer(s) that make up the arrangement. The frequency mixing system uses a feed-forward arrangement to reduce the distortion emanating from a single mixer due to a signal power level which would result in a frequency converted signal outside the dynamic range of the mixer. For example, the frequency mixing system splits an input signal onto a first path and a second path. On the first path, a first mixer frequency mixes the signal to produce a frequency converted signal with distortion, such as intermodulation distortion. On the second path, the amplitude of the signal is attenuated then frequency mixed by a second mixer to produce a frequency converted signal with a low and/or insignificant level of distortion.

Abstract: The present invention relates to a frequency conversion receiver at low intermediary frequency including a first analog mixer of a received signal with a signal coming from a local oscillator at a first conversion frequency and a second analog mixer of the incoming signal with the signal coming from the local oscillator out of phase by 90°. The receiver further includes, on the digital side, circuitry for detecting a possible phase difference and a possible gain difference between the signals of the two paths, the first conversion frequency corresponding to the central frequency of the received channel, plus half the channel frequency band.

Abstract: Two all pass filers (11, 12) with 90° phase-shifted different center frequencies are employed to pass an alternating signal S with jitters in the period to generate signals, S1 and S2, 90° phase-shifted from each other. A pulse generator (22) generates a sampling pulse Sp by detecting a zero cross point of the phase-shifted signal S2. A full-wave rectifier (21) rectifies full waves of the phase-shifted signal S1 and provides a rectified output to a sampling circuit (23), which extracts a peak value of the amplitude at the timing of the sampling pulse Sp.

Abstract: A transmitter includes a pair of electrodes separated in space, and transmit circuitry for varying the voltage difference applied across the electrodes in order to vary the spatial gradient of the electric potential field generated by the transmitter in accordance with the data to be transmitted. The receiver includes a pair of electrodes separated in space and receive circuitry which detects these variations in the quasi-electrostatic potential field in order to receive the transmitted data. Thus the receive electronics unit includes a detector connected to said electrodes for producing a signal which varies as the spatial gradient of the electric potential field across the receive electrodes varies but which does not depend on changes in potential within any given electrode.

Abstract: The phase of a transmitted signal is regulated in a device which is part of a system for electromagnetic signal transmission. The transmitted signal has periods when it contains information and periods when it does not contain information. The modulation position of a phase shifter which has a linear and a non-linear range is controlled. Power of the signal is amplified. Unwanted phase shifts in the signal transmitted by the device caused within the power amplifier are detected, and the information content of the signal is detected. The phase shifter is reset to a particular predetermined modulation position in the event of detection of the absence of information in the signal. The predetermined modulation position to which the phase shifter is reset is preferably situated within the linear range of the phase shifter.

Abstract: Apparatus for extracting a primary signal from a GSM signal containing co-channel interference partitions a signal burst into successive segments. Known characteristics of the GSM signal channel are used to estimate propagation path characteristics in respect of the first segment, and these are used to demodulate the segment. The demodulated signal is then used in a recursive process to estimate revised propagation path characteristics which are used for demodulating the subsequent segment. The demodulated segments and the estimated path characteristics are also used to derive segment signals representing the primary signal component alone, and these segment signals are used to reconstitute the primary signal. The derived primary signal can be subtracted from the received signal to extract the co-channel interfering signal. The apparatus functions with an omni-directional antenna, mounted for example on a moving vehicle.

Abstract: An approach for providing image rejection during signal down conversion involves phase shifting quadrature signals at a frequency other than the down converted center frequency. One or more phase shifters coupled to a summer/subtractor provide forty five (45) degrees and one hundred thirty five (135) degrees of phase shift with respect to two quadrature input signals. The one or more phase shifters perform the phase shifts of the quadrature input signals at a frequency other than the center frequency of the down-converted signal.

Abstract: A radio receiver providing compensation for a direct current offset which includes a first frequency converter for converting a signal received by the receiver to first and second intermediate frequency signals, each signal having an angular frequency &ohgr;r and being in phase quadrature with respect to each other. All analog-to-digital converter for converting the first and second intermediate frequency signals to first and second intermediate frequency digital signals, each having an angular frequency &ohgr;r and being in phase quadrature with respect to each other, a direct current offset being generated within the analog-to-digital converter. A second frequency converter for converting the first and second digital signals and the direct current offset to first and second baseband signals, and low pass filters each having a cutoff frequency &ohgr;T for removing frequency components of the first and second baseband signals which are higher than &ohgr;r.

Abstract: A radio FM receiver is provided with a receiver portion with quadrature channels for converting received radio frequency signals into center frequency quadrature signals, a center frequency filter circuit connected to the former for suppressing undesirable image frequencies, and a first quadrature PLL demodulator for demodulating the obtained center frequency quadrature signals, said PLL being tuned to the carrier frequency within the selected frequency band. An error detector is furthermore present for detecting amplitude and phase errors in the quadrature channels, which error detector in response to the quadrature components of the center frequency signals, the quadrature signals of a VCO in the quadrature PLL demodulator, and the filtered difference said quadrature components of the center frequency signal, supplies amplitude and phase correction signals to a quadrature channel correction network which is provided between the filter circuit and the quadrature PLL demodulator.

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.