Abstract: A system for detecting data spectrum distortion in a transmitted signal, in particular distortion caused by selective fading. The system includes: two blocks in parallel, which act on the spectrum average power of the input signal in an equal but opposite manner (i.e. they have equal slopes but act with opposite effect on the amplitude of the input signal versus frequency); two detectors which detect the average power output from the two respective blocks, each being associated with one of the blocks; and one comparitor for comparing the outputs of the two detectors. The system allows one to detect the asymmetries of the data spectrum and, by adding an AGC and a reference voltage, information related to the notch frequency f.sub.o is also obtained. The distortion measurement obtained in this manner allows one to generate a switching criterion, as a countermeasure for selective fadings in the transmitted signal.

Abstract: A method for processing electrical signals includes the steps of: storing a plurality of first digital data signals each representative of an instantaneous amplitude of a first input signal in a memory; selecting one of the first digital data signals in response to a second input signal; combining the selected one of the first digital data signals with a second digital data signal representative of a subsequent instantaneous amplitude of the first input signal, to produce a digital difference signal; producing a first output signal in response to the digital difference signal; and combining the digital difference signal and the selected first digital data signal to produce a modified digital data signal and for replacing the selected one of the first digital data signals with the modified digital data signal in the memory. The method can be performed by an equalizer in a circuit for compensating for amplitude variations in a radio frequency signal or by a comb notch filter.

Abstract: An interference signal suppression system and method that suppresses coherent jamming signals. The system comprises first and second receiving antennas that are physically separated from each other to generate non-coherent received signals of interest. The antennas are positioned to receive communication signals that are jammed with coherent energy. The separation distance is typically 40 to 50 wavelengths of the non-coherent scattered wave radio frequency signals. Phase and amplitude adjustment circuitry is provided that alters the phase and amplitude of the received signals such that the coherent received signals are balanced and out-of-phase. These signal are then summed in a summing circuit and the output of this circuit generates signals wherein the coherent signals are nulled and the non-coherent signals are detectable. The signal suppression system and method is independent of the direction of arrival of the coherent signals, which overcomes limitations of conventional techniques.

Abstract: Apparatus for demodulating information signals frequency-modulated on an RF carrier signal carrying spectral components within the audio frequency range, a pilot carrier signal having an imparted phase shift from the phase of the transmitted pilot carrier signal, and amplitude-modulated spectral components having another imparted phase shift in a subcarrier channel frequency range above the audio frequency range. The apparatus includes a demodulator for demodulating the frequency-modulated information signals to provide a detected composite signal which includes a detected pilot carrier characterized by an imparted phase shift due to the effects of multipath reception, and detected amplitude modulated spectral components exhibiting another multipath induced phase shift.

Abstract: A phaseshift network (2) exhibits approximately equal impedances to the outputs of an IQ mixer (10), over a range of modulation frequencies (Fm). The phaseshift network furthermore exhibits an approximately equal time delay for the I and Q modulated signals propagating therethrough. The phaseshift network includes a first branch having an input node for receiving a first frequency signal that varies within a range of frequencies about a frequency Fo. The first branch includes a phaseshifter for providing a frequency signal representative of the first input signal that is retarded by a first predetermined number of degrees. The phaseshift network further includes a second branch having an input node for receiving a second frequency signal that varies within a range of frequencies about the frequency Fo. The second branch includes a phaseshifter for providing a frequency signal representative of the second input signal that is advanced by a second predetermined number of degrees.

Abstract: A power amplifier arrangement includes a power divider for dividing the signal to be amplified into equal-amplitude components. Each component is amplified by a signal amplifying path. The amplified signals are applied to a phase-sensitive power combiner. The combined signal appears at the sum port and a phase-related difference signal appears at a difference port of the combiner. The difference signal is processed to produce a control signal for controlling the relative phases of the signals passing through the signal amplifying paths.

Abstract: An ultra-widebandwidth compressive receiver includes a power divider for processing a composite input signal consisting of individual input signals. The power divider provides a plurality of power divided signals to corresponding nondispersive delay lines. Each nondispersive delay line generates a unique time delay for each power divided composite signal. The unique time delay is generated in accordance with an arithmetic progression. The unique time delay has the effect of altering the phase of a corresponding individual input signal. The time delayed composite signals are provided to a frequency converter which heterodyne mixes them with local oscillator signals of frequencies which are a base frequency plus multiples of a reference signal frequency. The result is provided to a power combiner which re-combines the time delayed and frequency converted individual input signals in order to generate a group of narrow signal pulses that are separated in time according to their frequency.

Abstract: According to the receiving method for mobile reception has a plurality of individual receiving antennas, also known as diversity receiving method, on the individual antenna output signals an auxiliary modulation is superimposed and the antenna output signals are added to give a summation signal which as amplified selected intermediate-frequency summation signal is then demodulated in relation to amount and frequency or phase, the phase position of an individual signal in relation to the phase position of the summation signal and/or the amplitude contribution of an individual signal to the amplitude of the summation signal thereby being determined. This information is utilized for optimizing the useful signal with a view to optimum interference suppression for example in that the phases and/or amplitudes of the high-frequency individual signals are changed in dependence upon the phase position and/or amplitude contribution determined.

Abstract: In a radio receiver in accordance with the heterodyne principle or with the homodyne principle, two additional transmission channels are provided for interference suppression. The two additional transmission channels have a different degree of distortion. Either mixing with a heterodyne oscillator signal takes place in each of the two transmission channels and the resultant intermediate frequency signals or baseband signals are added in phase opposition to give a sum signal, or the output signals of the two additional transmission channels are added in phase opposition to give a sum signal and the resultant sum signal is mixed with a heterodyne oscillator signal to give an intermediate frequency signal or baseband signal. The signals obtained after addition and mixing and derived from the output signals of the two additional transmission channels are frequency-selected and demodulated, and the demodulated signal is used for gain control.

Abstract: A satellite transmission capturing method for the GPS receiver whereby PLL operation is stopped until the demodulation intensity of a demodulator reaches a predetermined level. The frequency of the reproduced carrier of the demodulator is consecutively changed in increments of a frequency range wider than the PLL capture range in search for satellite transmissions. This allows the demodulation intensity to reach the predetermined level in fewer frequency changing steps than ever before. Thus the time required to capture the desired satellite transmission is reduced. Where the integral time constant of a low pass filter in the demodulator is set to a value smaller than that in effect during PLL operation until the demodulation intensity of the demodulator reaches the predetermined level, a wide band demodulation intensity curve is used in search for satellite transmissions until that level is exceeded.

Abstract: A circuit array for frequency translation by means of quadrature heterodyne signals has very low quadrature errors even at very high frequencies and is monolithically integratable with little external circuitry. The circuit array includes a first mixer which receives a first portion of an input signal, a second mixer which receives a second portion of the input signal, and a heterodyne signal generator which receives a local oscillator signal and supplies quadrature heterodyne signals to the mixers. The heterodyne signal generator includes a control loop to ensure a 90.degree. phase shift between the quadrature heterodyne signals. The circuit array can be used in a modulator for a transmitter or in a demodulator for a receiver.

Abstract: A zero IF receiver which is capable of detecting short duration or CW signals and of operating over a large dynamic range includes an input terminal for receiving an input signal, a quadrature down-converter coupled to the input terminal for producing quadrature related, frequency down-converted signals in a pair of signal paths. These signal paths each include an amplifier having a substantially sinh.sup.-1 transfer characteristic so that the pair of signal paths produce substantially logarithmic quadrature related output signals which are coupled to a demodulator. The demodulator converts the quadrature related output signals into amplitude and frequency descriptions of the input signal relative to a center frequency of the receiver. The amplitude description is determined by selecting the one of the quadrature related output signals having the larger absolute value and applying an amplitude correction thereto.

Abstract: In accordance with the teachings of this invention, a multi-path distortion simulator is constructed having two paths, one path including a delay means, and both paths including phase shifters and attenuators. The phase shifters are closely matched, thereby compensating for drift and errors in the phase shifters. Similarly, the attenuators are closely matched, thereby compensating for drift and errors in the attenuators.

Abstract: A direct conversion receiver for demodulating an FM signal converted frequency down converts the signal to quadrature related baseband signals (I,Q). These signals are applied by way of respective d.c. blocking capacitors (16, 18) and differentiating circuits (26, 28) to a differential arctan demodulator (20). The action of the differentiating circuits (26, 28) is to remove any d.c. component in the I and Q signals and to perform a frequency shaping which enables the demodulator (20) to recover correctly the modulating information. Measures are disclosed to overcome the effects of 180 degree phase jumps which will occur when the direction of rotation of the phasor reverses and of frequency dependent amplitude scaling introduced into the differentiated signals (I', Q').

Abstract: A receiver for receiving a transmitted signal comprising first and second bandwidth limited component signals modulating a single high frequency carrier in phase quadrature with the first component signal as originally transmitted including an identification signal has a source of a reference signal subject to phase error. Circuitry combines the received transmitted component signals with the reference signal to provide first and second demodulated signals characteristic of the first and second component signals respectively. A detector responds to the first and second demodulated signals to provide first and second detected components of the identification signal. Feedback circuitry responds to the detected components of the identification signal by providing a correction signal that is applied to the source of reference signal to reduce the phase error.

Abstract: A high-power high-isolation switch for high-power devices which switch power to one of several alternative output ports. Unwanted leakage is attenuated and high-isolation between the output ports is obtained. In addition, protection against burn-out during abnormally high leakage conditions is provided where the devices employed are not self protecting.

Abstract: A frequency difference detector (FDD) implemented as a balanced quadricorrelator has an automatic gain control system (68) having inputs capacitively coupled to the quadrature related, baseband frequency paths from the front end mixers (12,14). The a.g.c. system (68) has quadrature related mixers (78,80) coupled to said inputs for frequency up-converting the baseband signals to an intermediate frequency. The IF signals from the mixers are summed in a summing circuit (82) and subsequently squared in a squaring circuit (86). Any ripple in the output of the squaring circuit is removed by low pass filtering to produce a d.c. control signal which is applied to gain controlled amplifiers (22,24) present in said baseband frequency paths in order to render the output (V.sub.o) of the FDD less sensitive to variations in the input signal (V.sub.i).

Abstract: A correction circuit for a digital signal pair having an in-phase signal and a quadrature signal includes a value determining stage and an error-detecting stage. The value-determining stage determines a maximum value and a minimum value for the in-phase signal, a maximum value and a minimum value for the quadrature signal, and two held values for the quadrature signal that correspond to the maximum and minimum values of the in-phase signal. These signals are used in the error-detecting stage to derive an in-phase offset error signal, a quadrature offset error signal, a phase-error signal, and an amplitude-error signal from which an in-phase-offset-correcting signal, a quadrature-offset-correcting signal, a quadrature phase-correcting signal, and quadrature amplitude-correcting signal are formed by associated controllers.

Abstract: A dual branch receiver in which the frequency of the first local oscillator (32) is offset by a few hundred hertz from the input carrier in order to provide separate wanted and image components. Gain and phase control are provided to compensate for differences between the two branches (12, 14), the image signal being used to provide the required error signals. However in the event of the modulation frequency being equal to the offset frequency, the image signals cannot be distinguished from the wanted signals thus inhibiting gain and phase control. This drawback is overcome in the receiver in accordance with the present invention by wobbling the frequency provided by the first local oscillator (28). The wobbling frequency is preferably sub-audible so as not to be discernable to the ear.

Abstract: A noise reduction apparatus in which an input signal is supplied to a first signal path (2) including a variable low-pass filter (2) and a second signal path (1), a control circuit (4) control is such that a cut-off frequency of the variable low-pass filter (2) is varied in accordance with a frequency of the input signal S(1), and an output signal is obtained from the first signal path when noise is generated and from the second signal path when noise is not generated.

Abstract: A synchyronous receiver with direct mixing comprising a phase detector and an amplitude demodulator is provided with a square-law envelope detector and means for making the envelope signal audible or visible for tuning purposes.

Abstract: An FM interference suppressor comprises two FM demodulators, one of which is fed with an input signal via an envelope detector and is arranged to feed a zero frequency detector and a phase inverter to produce a baseband composite signal comprising wanted and unwanted modulation. The other FM demodulator is fed directly with an input signal directly to produce a baseband signal comprising the unwanted modulation alone. A combiner is provided for subtractively combining the baseband signal and the baseband composite signal to produce the wanted modulation signal.

Abstract: A lossless spatial filter having N input ports and N output ports and printed on a single substrate. The filer is used in combination with an antenna system which radiates wave energy signals into a selected angular region of space and into a desired radiation pattern. The aperture of the system includes a plurality of N antenna elements. The antenna elements are arranged along a predetermined path and each element is connected to only one output port of the spatial filter. A beam steering unit controls the direction of radiation. A signal generator supplies a power divider having N output signal ports each connected to a phase shifter controlled by the beam steering unit.

Abstract: A radio transmission system a base station comprises a plurality of transmitters arranged to transmit from the same site and having substantially the same output power, each transmitting on an individual channel within a dedicated block of contiguous channels. Receivers tuned to channels within said block of channels therefore require a limited image and adjacent channel rejection, of the order of 30 db. The receiver is preferably a direct conversion phasing receiver which has a local oscillator which can be tuned to a frequency within the block such that an image of any channel also falls within the block of channels. The system is suitable for local area radio systems such as paging or cordless telephones.

Abstract: In a receiving station having an adaptive receiving antenna, a phasing system comprises a plurality of reception paths receiving telecommunications signals derived from the same useful signal combined in transmission with a disturbing signal having a frequency band outside the frequency band of the useful signal, via a plurality of primary sources of the receiving antenna. The phasing system includes a narrowband filtering circuit for filtering the overall telecommunications signal in one of the reception paths to derive a reference signal undisturbed by the disturbing signal and solely dependent on the useful signal. In phasing circuits respectively assigned to the reception paths, the useful signal alone is set to a phase as close as possible to the phase of the reference signal in order to obtain, after signal summing at outputs of the phasing circuits, a maximum power using signal mixed with an attenuated scrambling signal.

Abstract: A signal detection apparatus wherein pulses of the reverse polarity to that of the signal pulse to be detected are detected from an input pulse signal, and thereafter the signal outputting path is cut off for a fixed period, so that noise pulses which have oscillating waveforms in both positive and negative polarites are segregated from the signal pulses which can be provided with a unipolarity, by making use of the difference in polarity, and thereby, the noise pulses are eliminated regardless of their pulse heights. Further, the signal input to the cut-off circuit is delayed for a fixed period of time so that the first peak of the noise pulses may be eliminated even if it is of the same polarity as that of the signal pulse.

Abstract: A digital pulse detection apparatus for correcting a distorted serial digital signal by differencing the signal and a delayed version of the signal in a differential amplifier to obtain the slope of the digital signal. The output signal from the differential amplifier is applied to a voltage hysteresis differential amplifier which provides the corrected digital output signal.

Abstract: The effects of multipath and other interference signals in communication receivers are reduced by implementing an adaptive array. The invention addresses a signal environment in which the directions of arrival and the time of arrival of the signal of interest and the unwanted multipath or interference signals are unknown. The feedback equation of the LMS adaptive array is changed so that a reference signal is not needed. The system uses the strongest received signal as the signal of interest and rejects the other received signals.

Abstract: An improved digital signal detector for indicating the presence of digital data used in a communication system. While attempting to detect valid data, the detector buffers an incoming signal in a first-in, first-out buffer and allows locally generated data, instead of the buffered signal, to be coupled to an output. After detecting valid data, the detector estimates where in the buffer valid data commenced and either releases data from that point or further delays the signal up to the maximum length of the buffer before releasing it to the output. The invention provides high sensitivity and rapid detection, reduces variation in detection time over previous methods, and allows locally generated data to be inserted into the signal path without loss of valid data.

Abstract: A frequency converter which is capable of rejecting unnecessary signals generated by image signals. The frequency converter has first and second local oscillation circuits which generate local oscillation signals whose frequencies are the same and whose phases are different by 90 degrees from each other. The converter further includes two mixer circuits, and a hybrid coupler. The mixer circuits generate two unnecessary signals whose phases are different by 90 degrees from each other. The hybrid coupler delays one unnecessary signal by a quarter of a wavelength to generate two unnecessary signals whose phases are different by 180 degrees from each other, so that they are cancelled by each other.

Abstract: A space diversity reception system which minimizes the inband amplitude and/or phase dispersion by controlling the phase shifter is described. According to the present invention, the interference waves in the two antenna outputs are combined in anti-phase condition. The phase shifter control direction is decided by the sign of the two parameters. One of them is difference between two antenna levels at the center frequency of the pass-band, and the other is the difference of the combined signal levels at the extreme edges of the pass-band. The control means comprises four detectors for detecting said levels, two subtractors for providing said level differences between them, and the control circuit for deciding the phase shifter control direction.

Abstract: A noise removal circuit for use in partial discharge measuring device of a high voltage apparatus. The circuit includes a first phase shift/reduction device responsive to an input signal for passing it directly while delaying it by a predetermined time and for reducing the delayed signal from the directly passed signal a second phase shift/reduction device for passing an output of the first phase shift/reduction device directly while delaying the output by the predetermined time and for reducing the delayed signal from the directly passes signal, and a phase shift/multiplying device for directly passing an output signal of the second phase shift/reduction device while delaying it by a time twice the predetermined time and multiplying the directly passed signal with the delayed signal.

Abstract: In a time division multiple access communication system including a nonlinear signal processing element, an accurate carrier power-to-noise ratio is obtained by the circuit of the present invention. In the inventive circuit, noise power is determined solely by the quadrature noise and, hence, is free from measurement errors caused by the compression of in-phase noise associated with a non-linear element in the transmission channel.

Abstract: Certain, but not all AM stereo radio broadcasting and reception systems suffer from a severe form of reception anomaly wherein the perceived stereo image moves from side to side, back and forth, which effect has come to be known as "Stereo Platform Motion" or simply "Platform Motion". A prior art patent proposed a method for sensing reception conditions conductive to Platform Motion and then switching the receiver from stereo to monophonic reception to avoid Platform Motion. The present invention enables the AM stereo receiver to maintain stereo operation under such reception conditions, and instead of switching the receiver to monophonic operation, it switches the receiver to a different method of stereo reception that does not suffer from Platform Motion.

Abstract: The present invention relates to a bootstrapping cross-polarization canceler which includes a noise-blanking limiter in the path before a correlation detector, and a processor which uses the output from the correlation detector to provide cross-polarization cancellation continuously or just during an outage condition where orthogonally received signals from a communication path include error rates which exceed a predetermined threshold. Alternatively, the processor can use the output of a pseudo error detection, which detects the error rate of the orthogonally received signals, when the error rates in the received signals are below the predetermined threshold in order to achieve convergence and cross-polarization cancellation in the canceler during a non-outage period.

Abstract: An analog signal which is affected by impulse noise is applied to a timing circuit that generates a sampling pulse in response to a noise impulse introduced in the desired signal. This noise-affected signal is also applied to a holding circuit which passes it in the absence of the sampling pulse and holds it in the presence of the sampling pulse to derive therefrom a modified analog signal. A differentiator generates a signal representative of the time-varying rate of the analog signal. A sampling circuit samples the rate representative signal in response to the sampling pulse and holds the sampled signal for the duration of the sampling pulse to derive therefrom a rectangular pulse, so that the amplitude and polarity of the rectangular pulse represent the gradient and polarity of the noise-affected portion of the signal. The rectangular pulse is integrated linearly at a rate variable as a function of the amplitude of the rectangular pulse to generate a ramp voltage.

Abstract: A multipath distortion reducing circuit particularly adapted for use with stereophonic receiving circuits in which the amount of mixing between right and left channels is reduced. In accordance with the invention, the envelope of the received FM signal is AM detected, and the envelope detected circuit is multiplied by the FM detected signal differentiated to provide a distortion cancelling signal. The distortion cancelling signal is summed with the detected FM signal to provide an output having a reduced multipath distortion component.

Abstract: An electronic noise filtration system for use in improving the signal to noise ratio of acoustic data transmitted from a downhole transducer in a measurement while drilling system. Signals from a pair of receiving acoustic transducers located in the mud flow path directed downhole are input to a differencing amplifier. The RMS output of the amplifier is converted from an analog to a digital signal and then processed by a computer programmed with a least mean squares technique for minimizing the signal. The input from one receiving transducer is routed through a delay line wherein a programmable clock controls the timing of the signal delay. The delay time is controlled and adjusted by the computer's calculation of the frequency with which the clock should drive the delay line to minimize the difference between the two received transducer signals. This function minimizes ambient noise in the acoustic transmission line formed by the column of drilling fluids when no data transmissions are being made.

Abstract: A device for aligning the phase and amplitude of a quadrature-detected coent two-channel receiver utilizing a mixer in each channel comprising a circuit for providing a sweep frequency signal to each receiver channel; a circuit for detecting the envelopes of the receiver channels at the outputs of the mixers and determining the voltage difference between the envelopes; and a circuit for controlling the amplitude level in one of the receiver channels in accordance with this voltage difference. Simultaneously, the output signals from the two mixers are added with the resulting sum signal being envelope-detected, and also subtracted from each other with the resulting difference signal being envelope-detected. The sum envelope and the difference envelope are subtracted from each other to generate a control signal for controlling the phase of one of the mixer local oscillator signals to ensure that the mixer local oscillator signals are in phase quadrature.

Abstract: In an AM stereo system wherein a low frequency pilot tone is added to the difference channel signal before modulation of the carrier, "image shifting" and audio distortion in a receiver, due to residual pilot tone signal, are removed by separating out a portion of the pilot tone after it has been filtered and phase shifed for enabling the stereo mode of operation. The separated signal is then inverted and delayed appropriately for each of the PLL and audio circuits.

Abstract: In radio communications receivers for use on frequency hopping radio communications networks, the received signal in each hop period is analyzed and assigned a quality value. If more than one signal is present during the hop period it is determined that more than one network has changed to the same frequency. Similarly if the received signal is out of synchronism it is determined that more than one network has changed to the same frequency. When more than one network has changed to the same frequency, the received signal is not output by the receiver but is replaced by an earlier (or later) received signal.

Abstract: Circuitry for use in an IF combiner, where main and diversity receiver path signals are combined. The circuitry generates an error signal for the purpose of controlling the phase of one of these signals by deriving a broad-band phase-modulated feedback path version of the signal. No modulation is introduced into the message channel. The feedback path version of the signal is quadrature modulated and combined with signals from the main and diversity receiver paths to generate an error signal providing maximum control loop sensitivity.

Abstract: The present invention relates to a space diversity combiner which includes two branches wherein separate multipath signals received from a remote source are propagated. The branch signals are combined and the combiner output signal is used for obtaining noncoherent spectrum measurements which are in turn used to account for both dispersion and noise in controlling the relative amplitudes and phases of the two branch signals to provide a maximum performance measure for the combiner.

Abstract: In an interference elimination device for use in a digital microwave communication system in which an interference component results from at least one different microwave communication system sharing a frequency band in common, a controller (21) controls a device input signal so that a controlled signal thereby produced may include a controlled component which is equal in amplitude to the interference component and be antiphase relative thereto. The controlled signal is subtracted from the device input signal to provide a difference signal which is free from the interference component. Together with the device input signal, the difference signal is supplied to a control signal producing circuit (41) for producing an amplitude and a phase control signal for the controller. Instead of the device input signal, an interference signal derived by causing the device input signal to pass through a narrow-band filter (11 or 12) may be delivered to the controller and the control signal producing circuit.

Abstract: A multipath interference reduction system for mobile subscriber access systems, each occupying one of a plurality of time slot channels. Interference caused by multipath returns is eliminated in the receiver portion of digital signal communications apparatus by a plurality of cascaded signal subtraction units wherein the detected signal is successively delayed by increasing multiples of the pulsewidth of the main lobe, varied in amplitude and subtracted from itself until all the multipath amplitudes of significance are subtracted out of the composite received signal.

Abstract: The present invention provides a method and apparatus for scrambling and unscrambling television signals to prevent reception of acceptable signals by an unauthorized television receiver while maintaining the television signal recoverable by an authorized receiver. The present invention can also be used for reducing the necessary carrier signal power of a television transmitter.A transmitter (12) passes a television signal through at least one linear filter (30, 32 and 34) of the type that produces multiple time delayed signals of differing time delays.A receiver (14) receives the multiple time delayed signals from the transmitter and passes them through at least one linear filter (64, 66 and 68) to add the signals together so that one signal representative of the original is reinforced, allowing acceptable reception by an authorized viewer.In one arrangement, the linear filters are SAW devices.

Abstract: The fade character of a received double-sideband, phase coherent signal is determined from the location of the fade notch frequency, (.omega..sub.F) relative to the center (.omega..sub.c) of the received signal frequency spectrum and the phase between fundamental components of first (P.sub.1) and second (P.sub.2) product signals. These product signals are derived (401, 403, 411, 413, 419, 420, 421 or 801, 802, 803, 805, 811) using first (.omega..sub.1) and second (.omega..sub.2) spectral components that are symmetrically disposed about the center of the received signal frequency spectrum. The fundamental components of each product signal are at a common frequency.

Abstract: A space diversity receiver with a combiner in which the useful signals of two space diversity receiver branches are connected together with a summing amplifier in the IF frequency band, and wherein an electronically controlled phase corrector P is mounted in one of the receiver branches and in which a phase monitoring circuit provides an output signal to control the phase corrector and is connected at the output of the electronic phase corrector between the two receiving branches. The space diversity receiver is constructed in the simplest possible manner with the lowest possible electrical interference and provides that the phase monitoring circuit consists of a phase discriminator D1 to which the signal from one reception branch is supplied through an automatically gain control amplifier RV2 without phase shift and the signal from the other receiving branch is supplied with an identical automatically gain controlled amplifier RV1 and through a 90-degree phase shifter.

Abstract: The effects of crosstalk of an FM carrier from a first signal channel into a second signal channel are reduced by a variable-frequency notch filter coupled in the second channel. The frequency of the notch in the transmission characteristic of the filter is controlled to track the frequency of the FM carrier. Signals in the second channel at the frequency of the FM carrier are attenuated, and therefore the crosstalk signal is attenuated and its effects reduced.

Abstract: A pre-detection maximal ratio combining system for a plurality of received signals is provided in which a plurality of control devices are arranged for controlling the phase and amplitude of each of a number of pre-detection signals corresponding to the received signals. The control devices operate by correlating the mutually orthogonal components of the pre-detection signals with a reference comparison signal, which is derived by combining the outputs of the several control devices into a combined signal, and normalizing the amplitude thereof.