Abstract: A radio receiver front end is disclosed that processes a multi-carrier signal with a large dynamic range. An illustrative embodiment of the present invention incorporates both feedforward and feedback mechanisms to suppress the amplitude of spurious carrier signals so as to prevent those signals from flooding the dynamic range of the mixer that mixes down the multi-carrier signal.

Abstract: A process and system for improving the detection of signals in additive correlated non-Gaussian noise using multichannel data. This improves detection performance of receivers through the signal processing architecture when the observation data X(n) is first split into an upper and lower path. In the upper path, the known signal is first subtracted from the data and then passed directly to the prediction error filter. The output of the prediction error filters are then input to the zero-mean non-linear processor and their associated estimated variances are used to determine H.sub.0 and H.sub.1 where H.sub.0 denotes the condition where no signal is present in the data and H.sub.1 denotes the signal present case.

Abstract: An inversion prevention device to prevent inversion and provide the best S/N ratio detects a point where the zero crossing is missing from a quantized FM signal. An output is provided by switching between the digital FM signal and the output signal of at least one sideband suppression filter based on a result of the inversion detection. Alternatively, an output is provided by switching between the digital FM signal and a specified value based on a result of the inversion detection. As a further alternative, an output is provided by switching between the digital FM signal, the output signal of a low-sideband emphasis filter and the output signal of a sideband suppression filter based on a result of the inversion detection.

Abstract: A generalized noise canceler for canceling noise in a channel having noise composed of correlated noise components. The noise canceler is realized with a finite number of cascade networks, each network being composed of an inner product filter is series with another filter wherein both filters have characteristics determined from a eigenvector equations expressed in terms of the channel operator and noise operator.

Abstract: A composite signal recognizer, separator, and FM demodulator apparatus for processing received radio signals. The receiver utilizes N demodulators to process a received signal, where N is equal to or greater than the number of co-channel signals or perceived interference. Detailed in both cross-coupled and cascaded fashion, the receiver first tracks to a predominant (stronger) signal, and regeneratively improves track on other (weaker) signals by subtracting the predominant signal or the predominant noise portion from the input of further demodulation stages.

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 method is provided for obtaining a reference signal for suppressing an interfering signal received by a radio receiver system. The radio receiver system receives the interfering signal on an antenna along with a signal of interest. An electrically conducting structure on which is present an interfering signal corresponding to the interfering signal present on the antenna and close to the antenna is selected and the interfering signal present on the conducting surface is sampled to obtain a reference signal. The reference signal is provided to an interference cancellation system which generates a cancellation signal used to suppress the interfering signal received by the radio receiver system.

Abstract: A noise attenuation circuit (43) is provided for reducing noise in an RF stage of an AM radio receiver. A RF amplifier (44) amplifies an RF signal with amplitude modulated audio information from the signal path of an AM receiver. An AM detector (46) receives the amplified RF signal and removes the audio information. A high-pass filter (47) filters out a majority of the audio information. A noise pulse couples through the hi-pass filter (47) which is detected by a pulse detector (48) when above a predetermined threshold voltage. The pulse detector (48) enables an RF timer (49) for generating a pulse of a predetermined width. The RF timer enables a RF attenuator (51) for attenuating the RF signal in the signal path of the AM receiver. The RF attenuator (51) attenuates an average noise pulse to a level approximately equal to the magnitude of an unmodulated RF signal.

Abstract: A radio system and interference cancellation system for use with the radio system include a receiving radio and a transmitting radio which are coupled to a common antenna. A reference coupler provides a reference signal in response to the signal transmitted by the transmitting radio and provides the reference signal to a vector modulator and a synchronous detector. A receiver coupler is responsive to the transmitted signal which is reflected by the antenna and to the signal which is desired to be received and provides a received signal containing an interfering signal component and a desired signal component. An error coupler samples the received signal which includes any residual interfering signal component after cancellation, and provides an error signal to the synchronous detector. The synchronous detector compares the reference signal with the error signal and provides a detector output to the vector modulator.

Abstract: A method and an apparatus for adaptively canceling an interference signal in any D/U ratio is disclosed. The method and apparatus are directed to being implemented in a two-branch space-diversity system having an array of first and second receivers assigned to a first diversity branch and a second diversity branch, respectively. The feature resides in the ratiow.sub.2 /w.sub.1 =(m.sub.1 g.sub.1 m.sub.2 g.sub.2 *) / (m.sub.2.sup.2 g.sub.2 g.sub.2 *),wherein w.sub.1 and w.sub.2 are the weights by which a first branch signal and a second branch signal, respectively, are to be multiplied, m.sub.1 and m.sub.2 are the gains of the first and second receivers, and g.sub.1 and g.sub.2 are the transmission coefficients of the interference signals received by the first and second receiver, respectively.

Abstract: A GPS receiver downconverter combines on a single integrated circuit, a first super-heterodyne mixer, a voltage controlled oscillator, a phase locked loop, a pair of quadrature mixers and a pair of quantizers with in-phase and quadrature-phase sampler outputs operable at twenty-five MHz and 2.5 MHz. Emitter-coupled logic and special low-voltage bipolar semiconductor technology are combined for 3.3 volt operation at under one hundred milliwatts.

Abstract: An enhanced nonlinear signal processor for RFI suppression using either biased null zone amplifier or a biased inverting limiter. Two or more nonlinear interference processors are connected in cascade. As a result, a deliberate tracking error, selected to provide only a small amount of relative interference rejection, is introduced into each processor. The effect of each stage is cumulative until some limit to performance improvement, determined by the input/output characteristic of each stage, is reached. The benefits of this discovery are increased dynamic range capability (higher levels of interference-to-wanted signal ratio can be fully rejected), simplification of gain control, and increased flexibility in hardware implementation options resulting from reduced sensitivity to RFI tracking error.

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 cellular receiver range extender has an input terminal connectable to an antenna and an output terminal to which may be connected a microwave radio receiver for cellular communication signals. The input terminal directs RF signals to a bandpass preselector covering a frequency spectrum of 825 MHz to 890 MHz leading to a low-noise preamplifier for amplifying the preselected RF signals. A divider coupled to the preamplifier feeds signals from the preamplifier at equal power levels into first and second RF paths. The first path includes a band pass filter covering the reverse cellular communication channel RF signal band from 825 MHz to 845 MHz, and the second path includes a band pass filter covering the forward cellular communication channel RF signal band from 870 MHz to 890 MHz. In the first path reverse channel signals are amplified by a low-noise amplifier while in the second path forward channel signals are attenuated.

Abstract: A circuit which restores portions of an input signal lost due to clipping distortion includes a comparator which locates the portions of the input signal which have been subject to clipping distortion and generates a pulse signal where each pulse corresponds to a clipped portion of the input signal. This pulse signal is used to generate parabolic pulses which are combined with the input signal to generate a modified signal that approximates the input signal without the clipping distortion. One circuit generates the pulse signals by controlling an oscillator to produce a parabolic pulse train which changes in frequency and amplitude to match each pulse of the pulse signal and then selecting one of the parabolic pulses for each pulse of the pulse signal. Another circuit generates the parabolic pulses by doubly integrating the pulses of the pulse signal.

Abstract: A partial response Trellis decoder that performs trellis coded modulation in a high definition television (HDTV) having a specific and detailed configuration and includes a distance mapper for calculating first, second, third and fourth Euclidean distances between the input signal and a reference value; a Viterbi decoder for Viterbi decoding the first, second, third and fourth Euclidean distances calculated by the distance mapper; a first delay for delaying and outputting the Yiterbi decoded data for each Euclidean distance; a ruler selector for selecting a ruler type signal based on the signals output by the first delay; and a slicer for slicing the selected ruler type signal and the input signal.

Abstract: A communications system is disclosed for spectrum sharing of a microwave point-to-point system and a PCS system. The invention comprises a microwave communications system. This system includes a transmitter for transmitting a first signal and a second signal. The first signal and the second signal are oppositely circularly polarized electromagnetic waves within a predefined frequency range. The system also includes a receiver for receiving the first and second signals. In the preferred embodiment of the present invention the receiver may further include a first microwave receiver for receiving the first signal. It would then include a second receiver for receiving the second signal. The receiver would also include signal combining circuitry for combining the first signal and the second signal to generate a composite signal. It would then include a signal comparator to generate a comparison signal by comparing the average value of the amplitude of the composite signal with a predetermined value.

Abstract: The electricity consumption of a telephone kiosk is reduced when quiescent by a clock handler which varies the frequency of the pulses sent to the microprocessor for operating it.

Abstract: An FM receiver comprising a local oscillator (23), a heterodyning stage (24) and a demodulator stage (33). The heterodyning stage has a signal producing arrangement and a multiplier arrangement. The signal producing arrangement (25,26,27,29,30,31,32) produces n signals a.sub.1 . . . a.sub.n wherein each signal consists of a message signal modulated at the intermediate frequency of the receiver, and these signals a.sub.1 . . . a.sub.n are related by the expressiona.sub.i =cos [.omega..sub.IF t+k.sub.f .intg..sup.t A(t)*dt+.OMEGA.+.pi.*(.sup.i /n)]where .omega..sub.IF, k.sub.f and .OMEGA. are constants, n is a positive integer greater than or equal to 2 and i takes the values of all positive integers up to and including n. The multiplier arrangement (28) multiplies the n signals together and thus produces an output signal from the heterodyning stage, wherein the message signal is modulated at a frequency of n times the intermediate frequency.

Abstract: A postdistortion network for a receiver at a receiver location in an optical transmission system is disclosed. The receiver converts an optical signal carried over an optical transmission link to an RF signal. The postdistortion network includes an input terminal for receiving the RF signal and a distortion generator for generating a distortion signal from the RF signal. An adjusting circuit for adjusts the phase and amplitude of the distortion signal based on distortion at said receiver location. The adjusted distortion signal is combined with the RF signal in order to cancel or substantially suppress distortion in the RF input signal. The present invention permits individual receivers in an optical transmission system to be compensated for distortion which may be unique to that receiver location. A communications system including a predistortion network and a postdistortion network is also disclosed.

Abstract: An equalizer employed with a receiver for cancelling an interfering signal due to low cross-polarization isolation. The present equalizer provides a simple and inexpensive cross-polarization interference cancellation system. The equalizer uses an error signal generated in a residual carrier detector to determine the magnitude of an interfering signal and inputs a cancelling signal to the co-polarized channel until power in the error signal is minimized. In the equalizer, the determination of the magnitude of the interfering signal is performed at baseband (after demodulation but prior to data detection) and the cancellation is performed at RF, prior to dispersive microwave elements. In the receiver, co- and cross-polarized signals are received and amplified. A copy of the cross channel input signal is supplied to each receiver channel. An RF vector modulator is used to control the phase and amplitude of the cross-polarized signal prior to summation with a desired co-polarized signal.

Abstract: A predistortion circuit for an optical communications system includes a main path for an RF modulating signal and a predistortion path for a predistortion signal, which signals are combined to modulate a laser diode. The distortion path includes a distortion generator which generates a distortion signal which is substantially the same as the distortion generated by the modulation of the transmission system with the RF modulating signals. In one implementation, the distortion generator comprises a square law device which preferably is a field effect type device. The square law device operational characteristic closely mimics the major component of distortion in optical communications systems, composite second order (CSO) distortion. In a second implementation, two square law devices are coupled in an anti-phase arrangement to substantially cancel odd order distortion components from the distortion signal and to enhance even order distortion components, particularly CSO.

Abstract: A radio receiver front end having both feedforward and feedback mechanisms to suppress the amplitude of spurious signals so as to prevent those signals from flooding the dynamic range of the mixer of the front end. An illustrative embodiment of the present invention comprises splitting the input signal into a first signal and a second signal, creating a third signal based on the difference of the first signal and a difference signal, mixing down the third signal with a first oscillatory signal, isolating a feedback signal from the mixed down signal, mixing up the feedback signal with a second oscillatory signal and creating the difference signal based on the difference of the second signal and the mixed up signal.

Abstract: A high frequency transmitter comprises a large number of narrowband channels spaced over a broad bandwidth transmission. In one arrangement input data to be transmitted is demultiplexed (1101) so that sections of data are transmitted in groups of channels at 50 baud (say), each 50 baud channel produces a number of diversity channels modulated using difference phase shift key (DPSK) (103) and then added (105) for transmission. In the receiver, coherent summation (803) of close-bunched channels can be used and semi-coherent channel addition (805) can be used across the complete bandwidth. The received signal is convened to digital form then processed by an FFT circuit to produce frequency bins corresponding to the transmitted diversity channel frequencies. DPSK demodulation is carried out and running averages are carried out in each channel to determine the proportion of times that the phase difference falls within allowed limits (907).

Abstract: An FM noise reduction circuit including a level detection circuit receiving an intermediate frequency signal. The level detection circuit rectifies the intermediate frequency signal, and outputs a rectified intermediate frequency signal. A first frequency filter passes the rectified intermediate frequency signal in a first frequency range, and outputs a first voltage responsive to the portion of the rectified intermediate frequency signal passed in the first frequency range. A first interference signal detection circuit includes a second frequency filter. The second frequency filter passes the rectified intermediate frequency signal in a second frequency range and outputs a second voltage responsive to the portion of the rectified intermediate frequency signal passed in the second frequency range. The second interference signal detection circuit includes a third frequency filter.

Abstract: In the following manner, a receiver that receives quadrature modulated signals may determine desired components of the quadrature modulated signals by minimizing effects of transmitted distortion produced by gain, phase, or gain-phase imbalance. A quadrature modulated signal that includes a desired component, a fading component, and a transmitter distortion component is received by the receiver, wherein the transmitter distortion component includes a conjugate component and an imbalance component. The receiver estimates the fading component, the conjugate component, and the imbalance component and determines the desired component based on these estimates and the quadrature modulated signal.

Abstract: It is desirable that a cordless telephone system include a single base unit and at least two remote handunits. With such a system, two users may maintain participation in a three-way conversation while being free to move about within reasonable transmitting distance to and from the base unit. Circuitry is provided in which the signal received from one handunit is transmitted to the other handunit, and sidetone from one handunit is transmitted back to that handunit. The base unit comprises first and second double conversion intermediate frequency arrangements with respective first IF frequency portions being tuned away from a nominal frequency value by a substantially equal amount in opposite directions.

Abstract: An interference wave removing apparatus removing interference wave between angle diversity branches is disclosed. This apparatus is suitable for microwave communication beyond line-of-sight. The apparatus comprises a first reception unit for main beam, a second reception unit for angle beam, a first correlator for generating a first correlation signal corresponding to the first reception unit, a second correlator for generating a second correlation signal corresponding to the second reception unit, a first multiplier for multiplying an output of the first reception unit and the first correlation signal, a second multiplier for multiplying an output of the second reception unit and the second correlation signal, a subtractor for subtracting an output of the first multiplier from an output of the second multiplier, a channel quality compensator for compensating for an output of the subtractor for the channel quality, and a delay element for delaying an output of the channel quality compensator.

Abstract: Improved automatic gain control for an amplifier is obtained by controlling the size of a null zone in a drive signal for the amplifier. The size of the null zone is controlled by estimating strength of an interference signal, and dynamically varying the size of the null zone based on the estimated strength of the interference signal. As a result, the amplifier rarely saturates, regardless of signal strength. The invention is useful to reduce the harmful effects of jamming or interference.

Abstract: The Radio Data System (RDS) protocol promulgated by the European Broadcasting Union provides for alternate frequencies (AF) for the same broadcast. Receivers periodically switch over to such an alternate frequency, leading to momentary crackling noises. In a radio receiver having a device for temporary switchover from a received frequency to some other frequency, substitute signals are inserted into the audio signals that are interrupted during the temporary switchover. The substitute signals are formed from the audio signals before and optionally also after the temporary switchover.

Abstract: Circuitry and concomitant methodology for demodulating Direct-Sequence, Spread-Spectrum Code-Division Multiple-Access (DS/SS CDMA) channel signal using multiple samples per transmitted symbol and a minimum mean squared error criterion to suppress interference. In one embodiment, a bank of cyclically shifted filters determined with reference to the conventional matched filter for CDMA is used to demodulate the channel signal. In another embodiment, a bank of sub-filters determined with reference to the conventional matched filter for CDMA is employed to demodulate the channel signal. In yet another embodiment, the output of a conventional matched filter is oversampled to demodulate the channel signal. Each embodiment utilizes a set of adaptive coefficients selected to minimize the mean square error between the transmitted symbol and detected symbol.

Abstract: This invention provides a method and circuit for separating a signal of interest from an angle modulated interfering signal in which a composite signal, including the signal of interest and the interfering signal, is used to produce first and second signals, the first signal being representative of the composite signal and the second signal being representative of the envelope of the composite signal. Selected components are removed from the second signal to produce a filtered signal. The filtered signal is mixed with the first signal, to produce an output signal including a component representative of the signal of interest having a greater spectral power density than other components of the output signal.

Abstract: A radio frequency receiver (300) typically contains electronic devices commonly used in amplifying or mixing circuits (315) which are seldom ideal. The non-ideal characteristics of these devices lead to intermodulation (IM) distortion. A measurement of the amplitude of the received signal (301) is taken both unattenuated (503) and attenuated (507). The difference between the two measurements is compared (511) to predetermined limits (L1, L2 or L3) wherein the received signal (310) is determined to be valid, invalid or unsure. A valid received signal is demodulated in the receiver (300). An invalid signal, confirming the presence of IM distortion, is rejected. The unsure signal may be rejected or demodulated as determined by the receiver designer. This type of signal characterization is particularly useful for cellular radiotelephones (101) attempting to gain access to the system provider (111) in which it is registered.

Abstract: In a receiver comprising a receiver filter (12) with a frequency attenuation band and a pilot oscillator (25) for generating a pilot oscillation signal with a pilot frequency in the frequency attenuation band, a coupler (26) couples the pilot oscillation signal and a filtered receiver signal of the receiver filter to form a coupled signal. A low noise amplifier (13) amplifies the coupled signal into an amplified signal which comprises an amplified receiver signal component derived from the filtered receiver signal and an amplified pilot oscillation signal component derived from the pilot oscillation signal. A branching filter (27) branches the amplified signal into the amplified receiver signal component and the amplified pilot oscillation signal. A pilot signal component detector unit (28) detects the amplified pilot oscillation signal component to produce a direct pilot signal.

Abstract: A method and circuit for suppressing periodic noise interference in a broadcast signal received by a receiver, in which, during reception of the broadcast signal a dip occurs in the amplitude of the received broadcast signal each time noise interference is present, each dip having a slope, by the steps of: determining the values of the amplitude of the received signal; setting a basic received signal threshold value which is less than the value of the received signal at a time when no noise interference is present; during each occurrence of noise interference, increasing the threshold value by an amount proportional to the slope of the corresponding dip in the amplitude of the received signal; and acting on the received signal to suppress noise interference during a time when the amplitude of the received signal is below the increased threshold value produced by the increasing step.

Abstract: The present invention relates to a method for eliminating noise in a signal. The frequency band of the signal is divided into sub-bands, whereafter the useful value of the signal of each sub-band is determined by comparing the signal level to a reference level, in which case a constant signal of substantially the same level as the reference level is suppressed as noise and a varying signal, defined as a useful signal, is combined, unsuppressed, with the useful signals of the other sub-bands. The frequency band of the channel is divided into sub-bands by means of an all-pass filter construction. The method can be implemented using an analog or a digital filter construction.

Abstract: A demodulation apparatus incorporating an adaptive equalizer, capable of realizing a highly reliable communication, lower power consumption, and a compact size. In the demodulation apparatus, an output of one of two demodulators, at least one of which including an equalizer, is selected according to a presence or absence of multipath which is determined from a non-coincidence of bit codes, eye apertures, bit error ratea, or a matched filter output, while the operation of the other demodulator is stopped for reduction of power consumption, by stopping a supply of power or clock signals to the other demodulator. In a case using a frequency offset detection unit and a frequency offset memory, one of these is selected according to a convergence or divergence of an error signal from an equalizer, while the operation of the other one is stopped for reduction of power consumption.

Abstract: A repeater diversity spread spectrum communication system provides substantially fade free communications between a transmitter (1) and a receiver (7). A transmitted signal is relayed through a plurality of linear communications repeaters (3-6) that produce copies of the transmitted signal, the copies each arriving through an independently fading signal path. The transmitter and/or the receiver may be mounted upon a mobile platform, and the plurality of repeaters may be terrestrial, or may be provided in satellites in low earth orbit or in geosynchronous earth orbit. The receiver processes the received signal copies to equalize them to one another in delay, frequency, and phase, and then combines the multiple received and equalized signal copies to produce a composite signal having a greatly reduced fading depth.

Abstract: A method for reconstructing an incomplete signal in a sub-band transmission system is disclosed. Signal degradation from signal loss in a sub-band transmission system may be avoided by formulating an error function, and finding an optimal signal which minimizes the error between the sub-band signals interpolated from received sub-band signals and the sub-band signals obtained by convolving an optimal reconstructed signal with the original analysis filters. The minimized system equation is solved to provide an optimal reconstructed output signal.

Abstract: A demodulation apparatus incorporating an adaptive equalizer, capable of realizing a highly reliable communication, lower power consumption, and a compact size. In the demodulation apparatus, an output of one of two demodulators, at least one of which including an equalizer, is selected according to a presence or absence of multipath which is determined from a non-coincidence of bit codes, eye apertures, bit error rates, or a matched filter output, while the operation of the other demodulator is stopped for reduction of power consumption, by stopping a supply of power or clock signals to the other demodulator. In a case using a frequency offset detection unit and a frequency offset memory, one of these is selected according to a convergence or divergence of an error signal from an equalizer, while the operation of the other one is stopped for reduction of power consumption.

Abstract: There is disclosed a noise eliminating device for an angle-modulated wave, in which a carrier amplitude fluctuation of an angle-modulated input wave is detected in a frequency difference detector to obtain a frequency variation signal corresponding to a frequency variation arising at an amplitude limiter from the carrier amplitude fluctuation. Noise caused by the amplitude fluctuation is eliminated from the angle-modulated input wave by subtracting the frequency variation signal from an output signal of the amplitude limiter after or before the frequency difference detector.

Abstract: Predetection noise bandwidth reduction is effected by a pre-averager capable of digitally averaging the samples of an input data signal over a single symbol, the averaging interval being defined by the input sampling rate divided by the output sampling rate. As the averaged sample is clocked to a suitable detector at a much slower rate than the input signal sampling rate the noise bandwidth at the input to the detector is reduced, the input to the detector having an improved signal to noise ratio as a result of the averaging process, and the rate at which such subsequent processing must operate is correspondingly reduced. The pre-averager may form a data filter when the output sampling rate is reduced to one sample per symbol of received data.

Abstract: A method and apparatus is disclosed for automatic elimination of frequency instabilities in a receiver frequency converter. Such instabilities result from temperature variations and mechanical vibrations of the local oscillator of a first stage converter. A marker signal is introduced into the first stage down converter mixer and is subjected to the same variations in frequency conversion as is the received signal from an antenna. Intermediate down converted received signals and an intermediate down converted marker signal are received by a second stage converter where such signals are applied to a mixer, the output of which is free of frequency variations introduced by the local oscillator of the first stage converter.

Abstract: Undesired signals detected by a main antenna are cancelled by corresponding interference cancelling signals. The output of the main antenna is frequency converted to IF region and decomposed into first and second main baseband components. Decision circuits are provided for making a decision on whether each of the first and second main baseband components exceeds each of multiple thresholds and produces multibit codes as well as error signals. Auxiliary antennas respectively detect the undesired signals and feed auxiliary frequency converters for translating the frequency of the respective outputs of the auxiliary antennas to the intermediate frequency. Auxiliary quadrature demodulators are provided for respectively decomposing the output of each auxiliary frequency converter into first and second auxiliary baseband components. Correlations are detected between the first auxiliary baseband components and the first error signal and between the second auxiliary baseband component and the second error signal.

Abstract: A microwave receiver self-test capability which includes at least two channels with each channel including an amplifier and an IF receiver, the microwave receiver, also including a local oscillator capable of mixing with either of said channels for providing an IF signal and a data modulated signal source capable of coupling with said local oscillator through one channel of said microwave receiver and thereby, generating a microwave test signal for the other of said channel of said microwave receiver.

Abstract: A receiver for receiving angle-modulated radio signals includes detecting occurrence of interference from adjacent channels when an evelope of demodulated signal of the received radio signals exceeds a threshold. This receiver improves the quality of received signals, attenuates them, limits the amplitude thereof, or blocks them and to insert interpolation signals in replacement thereof when the detection output is transmitted thereto.

Abstract: A real-time rejection circuit for passing low level desired signals in the resence of one or more strong, interfering signals. A chirp-Z transform system separates the various frequency components of a received signal into frequency segregated time domain signals. A power splitter separates the time domain signal into two paths. One path includes a modulator or switch that is normally biased "ON" for passing the time domain signal. The second path includes a diode detector that produces pulses of sufficient strength when a strong interfering component is present to override the bias and turn the modulator "OFF" for a sufficient period of time to attenuate the unwanted frequency components in the other path. The modulator output will primarily contain the low level desired frequency components that are passed through an inverse transform device for producing a frequency domain signal of the desired signal uncorrupted by unwanted signals.

Abstract: A transmission line switch allows a single output line (3) to be switched to one of two or more input lines (1,2) to which it is permanently connected at a common junction (4). Each input line (1,2) has an associated amplifier stage (10) which can be biased in a normal high gain (`on`) state, or in an isolation (`off`) state. Suitable biasing in the `off` state ensures that the amplifier stage output presents a low impedance to its own input line, the length (L) of which is chosen to reflect a high impedance at the junction (4) with the other lines. Correct design enables the return loss and insertion loss of the `on` path to be kept to low values while simultaneously offering a high insertion loss to the `off` path signals.

Abstract: A divider circuit arrangement in which in order to avoid dividing by zero the divisor (V.sub.d) is modified by the addition of an extra signal (X.sub.a) to form a modified divisor V'.sub.d =V.sub.d +X.sub.a and the dividend (V.sub.i) is modified by the addition of the product of the quotient (V.sub.o) and the extra signal (X.sub.a) to form a modified dividend V'.sub.i =V.sub.i +V.sub.o X.sub.a. A particular but not exclusive application of this divider circuit arrangement is in normalizing an ouptut signal from a dual branch receiver (not shown).

Abstract: A chirped backscatter filter 10 compares a received signal (RSIG) to a reference signal related to a transmitted signal (TSIG) and removes from RSIG the frequency component which is equal to TSIG in frequency. This removed frequency component corresponds to the frequency of the transmitter backscatter radiation. The filter of the invention adds a frequency offset (f.sub.n) to both RSIG and TSIG in mixers 12 and 14 before substracting one from the other in mixer 22. Thus, equal frequency components in both RSIG and TSIG, such as the backscatter radiation frequency component of RSIG, will equal f.sub.n. The frequencies resulting from this subtraction are thereafter passed through a notch filter 24 which is centered on f.sub.n and which passes all frequency components except f.sub.n. The output of the notch filter thus no longer has a frequency component associated with the backscatter frequency component.