Abstract: A method and circuit arrangement identifies the presence or absence of known frequencies in an input signal composed of a plurality of frequencies, whereby a frequency generator controlled by a reference frequency generates four switch signals having frequencies dependent upon the frequency to be identified and having a phase difference of 90.degree. and respectively one switch signal is mixed with the input signal in a respective mixer. The respective mixer products of two mixers are additively combined and are filtered through a respective filter for filtering AC components out, and the DC voltage component contained in the respective mixer product given the presence of the known frequency is evaluated with respect to the amplitude.

Abstract: To increase the fidelity of radio reception in a moving receiver, for example a car radio, the signals received from various antennas on the radio are mixed with a carrier in the receiver, and the resulting mixed signals, directly and 90.degree. phase-shifted, are added to a summing signal, in which, additionally, the phase positions of the direct and 90.degree. phase-shifted signals are changed in dependence on the phase difference between the respective intermediate frequency mixed signal and the overall summed signal in a direction to maximize the summed signal (u.sub.s).

Abstract: A diversity combiner is provided for combining two received radio signals having the same frequency and modulation. For each of the radio signals (s, s') there is included a mixer (1, 1') with an associated voltage controlled local oscillator (2, 2') and a following intermediate frequency filter (3, 3') for generating an intermediate frequency signal (m,m') and a phase comparator (5, 5') for comparing the intermediate frequency signal with a reference signal (a) originating from a weighted aggregate (e) of the intermediate frequency signals (m, m). Each phase comparator (5, 5') sends a signal responsive to the phase difference and which controls the frequency of the local oscillator (2, 2'). The weights of the sub signals can be varied such that the quotient of the contribution of the sub-signals to the aggregate can be caused to correspond to an arbitrary power, which is greater than or equal to one, of a corresponding quotient before the addition.

Abstract: A circuitry in a diversity unit of an FM receiver for a telephone system having at least two channels for receiving signals, and at least one phase-lock loop. The signals received by the channels which possibly differ from each in amplitude and frequency. Each channel comprises a mixer and a band-pass filter for forming an intermediate-frequency signal. The phase-lock loop has phase-lock branches operably connected between each mixer of the channels which comprises a frequency-phase comparator. The phase-lock loop equalizes the channel signals in phase and amplitude. The phase-lock loop further has a summation circuit for adding the channel signals which have been equalized. The frequency-phase comparator has a single phase-lock branch exiting therefrom along with a voltage-controlled oscillator connected to one of the mixers of one of the channels. The voltage-controlled oscillator has a switch on an input side thereof.

Abstract: For diversity reception from a plurality of antennas, particularly in an automotive vehicle (FIG. 4), the respectively received signals are mixed with a local oscillator signal to form a plurality of IF signals (u.sub.1 . . . u.sub.n). The respective IF signals are weighted with a weighting coefficient which is derived from a sum circuit of all the IF signals, and the respective IF signal, which weighting circuit includes an integrator to minimize temporal variations in the amplitude of the sum signal. The sum signal forms the actual IF signal, for further processing, and demodulating to derive an audio signal. Preferably, the signals from the antennas are branched, and the branch signals phase-shifted 90.degree., which, again, are weighted by similarly generated weighting coefficients, and the weighted, phase-shifted signals are combined in the adding or summing circuit (70) to form said eventual IF signal for demodulation.

Abstract: Diversity combiners for use in satellite and other communication systems. Such combiners are able to accommodate fast and dramatic signal fades and doppler shifts inherent in satellite communications by employing differential and common mode automatic phase control and differential and common mode signal weighting techniques. Phase control takes place in these combiners after signal weighting to decrease differential loop phase detector gradients and noise bandwidth as a function of signal-to-noise imbalance of the channels. An acquisition circuit is provided to deactivate the differential phase control loop when either signal falls below a predetermined level. During times when the faded signal reemerges, the combiner establishes optimal combining with minimum phase discontinuities on the output or phase lock reacquisition disturbances.

Abstract: A combined diversity receiving apparatus comprises first mixers for mixing receiving signals from plural antennas with a signal from a feedback circuit, band-pass filters connected to outputs of the first mixers and having a band width to pass a random phase component due to fading and a main component of a modulation signal among received signals, second mixers for mixing output signals of the band-pass filters with the received signals, a coupler for combining outputs of the second mixers, and a feedback circuit for feeding back the output signal of the coupler to the first mixers.

Abstract: A diversity reception of signals involves first and second mobile receivers which recover first and second baseband signals. The first and second receivers have first and second wave detectors, respectively, for generating output voltages corresponding to the strength of an FM modulated signal. When the difference in output voltages between the first and second detectors exceeds a predetermined value, a comparator gives an output detection signal. An adder circuit combines the first and second recovered baseband signals. First and second switching circuits selectively cut off the lower level one of the first or second recovered signal, which is then being supplied to the adder circuit. A third switching circuit adjusts the gain of the adder circuit. When the comparator does not give an output detection signal, the first and second switching circuits feed both the first and second recovered baseband signals to the adder circuit.

Abstract: A diversity receiving system for differential detection of minimum shift key (MSK) signals. The system may be advantageously implemented in order to realize high quality mobile satellite communication systems where shadowing is a significant problem and channel bandwidth and power are constrained. Signals from each of a plurality of receiving branches are translated to different intermediate frequencies which differ from each other by multiples of the transmitted signal symbol rate. The intermediate frequency signals are summed and detected via a common differential detector, the latter being followed by a low pass filter having a bandwidth corresponding to a fraction of the symbol rate. The plural signals are easily and stabely combined at an intermediate frequency stage without phase adjusters, signal quality measurement circuits or switching controllers.

Abstract: An apparatus for identifying multi-frequency signals, the received signals being processed in selective receivers after having passed through a digital bandpass filter. The input signal to the receivers is multiplied at sampling times by a coefficient from each of two sets of coefficients. The first set is obtained by multiplying a sine function by a weighting function and the other by multiplying the same sine function phase-shifted .pi./2 by the same weighting function. The product of multiplication is formed and squared individually for each one of the multiplications, and the squared results are summed to obtain a measure of the signal energy within the passband.

Abstract: An improvement to a baseband system having a plurality of down converters feeding a single baseband receiver for assuring the same mean time to intercept while maximizing the probability of intercept as a multi-band, autonomous receiver. All channels of the converter unit are operated simultaneously and a unique tag is added to the output signal from each of the down converters whereby the signal can be identified by the balance of the system as to its associated converter. In one embodiment, the tag comprises an amplitude notch appearing on the output signal at a different time following the receiver threshold being exceeded. In a second embodiment, the tag comprises a frequency step added to and/or subtracted from each output signal at the same time following the exceeding of the receiver threshold. In a third embodiment, the tag comprises a phase shift applied to the output signal.

Abstract: A diversity signal strength indicator for transmission site selection in a cellular-like mobile radio system produces an output strength indication signal which is proportional to the logarithm of the average strength of two diversity input signals. The two input diversity signals are time multiplexed together to form a composite signal, and a log amplifier/envelope detector then produces an intermediate log signal which is proportional to the logarithm of the envelope of the composite signal. The intermediate log signal is then operated on by a peak detector to produce a peak intermediate log signal which is then passed through a low pass filter to produce an output strength detection signal proportional to the average of the intermediate log signal and thus proportional to the logarithm of the average strength of the diversity input signal.

Abstract: A data communications system is described that covers a geographic area divided into a plurality of non-overlapping zones and includes a general communications controller (GCC), a plurality of channel communications modules (CCM) and associated transmitters and receivers, and a plurality of portable radios. Message signals carrying alphanumeric information are communicated between the GCC and the portable radios by way of a radio channel. Each CCM takes a signal strength measurement every time it receives a message signal from a portable radio. The GCC gathers the signal strength measurements from the CCM receivers receiving the same message signal and computes an adjusted signal strength for each zone. The GCC then selects the zone having the largest adjusted signal strength for determining the location of the portable radio that transmitted the message signal.

Abstract: A subscriber distribution terminal is connected to the transmission medium for serving a group of subscribers. Within the distribution control terminal is located a plurality of television converters. A local oscillator in each of the converters is controlled by a microprocessor, which establishes the channel selected from the multi-channel television signal received from the transmission medium. The output of each converter is connected to a subscriber drop which is connected to the subscribers television set.

Abstract: A signal switch and combining system for a radio communication system having two receivers (R.sub.A, R.sub.B) includes a comparator operable to determine which of the receiver output signal to noise ratios is the greatest at any instant. There is also a threshold detector arranged to determine when the difference between the two signal to noise ratios exceeds any one or more of a number of predetermined threshold levels. A gating network (GN) responds to the outputs of the comparator and threshold detector (CT) to control a switching and impedance network SZ. This controls the connection of ratio signals from the two receivers (R.sub.A, R.sub.B) to an output load. The network is arranged to connect to the load either one of the two radio signals or a combination of the two signals in one of a number of predetermined ratios. The signal to noise ratios of the two receiver output signals are conveniently indicated by the receiver automatic gain control signals.

Abstract: The stability of reception of information signals in a low-quality radio communication circuit is notably improved by a method and apparatus of diversity reception which, by means of the local oscillation frequencies of a plurality of receiving systems, permits one or more coherently interrelated received signals to be phase-locked in the phase-lock loops of the respective receiving systems and which, when any of the phase-lock loops has accidentally lost the phase-lock of the received signals, enables the lost phase-lock loop to resume normal phase-lock by borrowing and using, as its own local oscillation frequency, the local oscillation frequency of the phase-lock loop of one of the remaining receiving systems still locking the phases of the received signals.

Abstract: Flutter in received radio signals at and above 150 MHz is reduced by a system having a plurality of directional antennas with receiving patterns that can be caused to rotate to sweep in azimuth. The antenna that receives the strongest signal is stopped from sweeping until another antenna receives a stronger signal, at which time it is stopped from sweeping and the antenna that was stopped is swept. Signals from all antennas are combined in a maximal-ratio diversity receiver to provide a combination of the signals that is additive regardless of their relative phase.

Abstract: A diversity system utilizing a plurality of branches has been found for an angle modulated digital signal transmission. The received signal on each branch is modulated with a local signal which has the same period as the digital signal, and satisfies the orthogonal relationship with each other. The modulated signals are combined by simply summing them, and the combined signal is differentially detected. In the case of two branches, said orthogonal local signals are .sqroot.2/T.multidot. sin (2.pi./T)t, and .sqroot.2/T.multidot. cos (2.pi./T)t, where T is the bit duration of the digital signal, and said local modulation is the amplitude modulation. The present invention can provide the same diversity effect as the prior maximal ratio combining system, although the present invention does not utilize a complicated cophasing means between each branches.

Abstract: A device for producing a voice warning over a speaker which is also used with an entertainment sound production system such as a radio or cassette recorder. The voice warning device incorporates a switching device in the circuit between the speaker and a source of entertainment sound-bearing electric signals, and also incorporates a mechanism for selectively generating electric signals representing human voice sounds for conveying warnings. When a warning signal is being generated, the switching device is switched over from its state where it connects the speaker to the entertainment sound-bearing electric signals to its state where it connects the speaker to the warning signals. Optionally, several different speakers of an entertainment system may be selectively connected to said warning signals by several switching devices.

Abstract: In order to reduce bit errors resulting in a space-diversity broad-band digital radio receiver from selective fading, an amplitude dispersion detector detects the amplitude dispersion caused, if any, by the selective fading in each of IF signals produced by the space-diversity reception and produces a detector output having an amplitude variable with the detected amplitude dispersion and used in combining the IF signals. The detector may comprise three band-pass filters having different narrow passbands in the IF band to produce filter outputs with amplitudes dependent on first-order and second-order dispersion components of the amplitude dispersion. Alternatively, the detector may comprise a band-pass filter having a narrow passband repeatedly variable throughout the IF band at a lower frequency to produce a filter output with an amplitude variable with the first-order and the second-order dispersion components and, above all, with a notch-shaped dispersion component.

Abstract: A receiving system is disclosed that substantially instantaneously receives an RF signal. The inventive receiving system may be advantageously utilized at a central station of a mobile radio system for providing an omnidirectional receiving pattern. Both voice and digital information signals modulated on the RF signal transmitted from a mobile station are substantially instantaneously acquired by the central station. The receiving system includes an omnidirectional antenna configuration having a plurality of spatially disposed directional sector antennas, converting circuitry for converting the RF signals received by each directional sector antenna to an IF signal, IF bandpass filters for filtering each of the IF signals, and a maximal-ratio predetection diversity combiner for continuously combining the filtered IF signals to provide a composite IF signal so that any received RF signal is substantially instantaneously acquired.

Abstract: A radio signal receiving system has first and second signal receiving sections, the outputs of which are combined to provide a combined signal. The signal combiner has first and second input terminals for respectively receiving the outputs of the first and second receiving sections. First, second and third interlocking switches are interconnected so that, when two outputs are derived in a normal state, from the first and second receiving sections, the first and second switches are closed, with the third switch opened. When either of the first or second outputs is driven out of the normal state, the first or second switch receiving the normal signal and the third switch is closed, while the first or second switch, receiving the abnormal signal, is opened. This way, the remaining normal signal replaces the abnormal signal to maintain the impedance balance in the system.

Abstract: A method and apparatus for measuring Faraday rotation of a received rf signal. The disclosure describes a specific implementation of a simultaneous orthogonal polarization receiver which compensates for a 3 db loss due to splitting of a received signal into left circular and right circular polarization channels. The compensation is achieved by rf and modulation arraying utilizing a specific receiver array which also detects and measures Faraday rotation in the presence or absence of spin stabilization effects on a linear polarization vector. Either up-link or down-link measurement of Faraday rotation is possible utilizing the method and apparatus disclosed herein.

Abstract: An improved high speed digital communications diversity receiver using a forward adaptive transversal filter equalizer, having a plurality of weighting sections in each diversity channel to provide a combined weighting signal, wherein the required complex multiplications and correlations needed for weighting purposes are performed at IF frequencies, while the time-delayed combining operations for providing the desired combined weighted output signal are performed at baseband frequencies. Such an arrangement reduces the number of tapped delay lines normally needed for such transversal filter equalizer operation and further reduces the signal losses incurred in operating delay line devices at intermediate frequencies so that fewer large gain-bandwidth product amplifiers are required in the system than the number required in previously available systems using such forward transversal filter equalizers.

Abstract: A tropospheric scatter radio communication system uses a multiple signal diversity system in order to improve reliability of reception. A dual time diversity is used in which adjacent bits in a digital word are interleaved with bits from adjacent digital words so that more than one bit from a particular digital word is unlikly to be adversely affected by short term fading.

Abstract: A receiving system without antenna switching wherein signals received by two or more spaced antennas are heterodyned using local oscillation signals at frequencies spaced from each other by not less than the fundamental frequency of a modulating signal. The resultant intermediate frequency outputs are combined and detected to produce an output signal.

Abstract: An AM/AGC weighted diversity combiner utilizing the AGC and AM voltages f the AGC loops of a plurality of receivers for generating an optimum weighting signal or combining ratio.