Abstract: A device and method for correcting an amplitude slope in the frequency domain of an input signal. An amplitude slope is detected in parallel feedback loops that connect the combined output of two parallel out-of-band notch filters through a slope detection circuit to inputs of each of the two notch filters. Each feedback loop detects the energy at one of the high and low frequencies that define the frequency domain of the input signal, and provides a voltage indicative of the energy back to the notch filters to vary the Q of the notch filters, thereby correcting the amplitude slope. The energy is detected in each feedback loop by mixing the input signal with one of the high and low frequencies that define the frequency domain of the input signal, and filtering out all but the DC voltage indicative of the energy at the one frequency. The DC voltage changes the resistance of an element in the notch filters to vary Q.

Abstract: An IF limiting amplifier uses localized positive feedback in each amplifier stage to provide additional small signal gain while maintaining the limiting gain. The extra small signal gain results in higher overall sensitivity for the receiver at less bias current. The reduction in the number of stages needed to perform the same signal response results in a significant decrease in power consumption by the circuit.

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: An electric field level detecting apparatus includes an intermediate-frequency signal generator, an intermediate-frequency amplifier, an analog voltage generator, an analog/digital converter, N converting tables, and a control circuit. The variable attenuator receives an intermediate-frequency signal from the intermediate-frequency signal generator as an input and changes a passing attenuation value in accordance with an attenuation value set to be changed at N steps (N: arbitrary natural number) by a first control signal. Each of the N converting tables prestores a relationship between a digital voltage and an electric field strength of a radio frequency reception signal corresponding to the attenuation value set in the variable attenuator and converts the digital voltage from the analog/digital converter into an electric field level signal indicating a corresponding electric field strength to output the electric field level signal.

Abstract: An unwanted portion of a radio frequency signal spectrum appearing on a signal line (12) is adaptively canceled by first sampling the unwanted portion of the spectrum, and thereafter filtering the sample, typically at an intermediate frequency, to reduce signal losses. The first sample is then processed to yield a cancellation signal, having a variable phase. The cancellation signal is then injected into the signal spectrum after which time, the spectrum is again sampled. The second sample is correlated with the cancellation signal and the resultant correlation is employed to adjust the phase of the cancellation signal to maximize the cancellation of the unwanted portion of the spectrum.

Abstract: A radio receiver for an RF signal which is phase or frequency modulated by an information signal. The receiver has an analog receiving section which provides non-linear dynamic compression. The resulting analog signal is sampled and the samples are digitized by an A/D converter. The non-linear dynamic compression reduces the necessary number of quantizing steps in the A/D converter, which is less expensive, but thereby introduces non-linear distortion. To compensate such distortion, in the digital processing section of the receiver an expansion section is provided which processes the digital signal samples in accordance with the inverse of the non-linear dynamic compression characteristic. The resulting expanded digital sample values equalize the analog non-linear dynamic compression. The information signal is recovered from the expanded digital signals.

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: For suppressing interference signals in a multiplex signal an RC member which is preceded by a voltage divider is used. The voltage divider consists of a resistor and two diodes which are connected in parallel and in opposite directions and which perform a limitation with respect to a reference signal taken from the output of a fedback differential amplifier. The output signal of the RC member is applied to the non-inverting input of the differential amplifier. The limitation is carried out with respect to a reference signal corresponding to the signal smoothed by the RC member.

Abstract: A transceiver determines the signal quality of a desired signal and the strength of all received signals. When the signal quality of the desired signal is low, and the signal strength of all received signals is high, the receiver is adapted to operate in a higher current mode, thereby minimizing intermodulation distortion. Conversely, when the quality of the desired signal is low and the strength of all received signals is also low, or when the quality of the desired signal is above a threshold, the receiver operates in a lower current mode to conserve power and maximize battery lifetime. Also, when the transceiver adapts to operate in the higher current mode, a command is sent instructing a transmitting party to increase the quality of their message which may enable the listening transceiver to adapt (return) to a lower current mode.

Abstract: A frequency stabilization circuit for a PSK data packet receiver includes a reference oscillator for supplying a continuous reference signal to a limiter that supplies feeds received data packets to a phase locked loop detection circuit including a voltage controlled oscillator. The frequency of the continuous reference signal is close to the carrier frequency of the data packets and maintains the frequency of the voltage controlled oscillator close to the data packet carrier frequency between data packets. During data packets, the reference oscillator signal is "swamped out" by the limiter.

Abstract: A method and system for separating a noise signal into frequency components, then automatically performing noise reduction on the individual frequency components, and then recombining the processed frequency components to generate an output noise signal. The noise reduction parameters for each frequency component may be independently set. The output noise signal generated during performance of the invention will typically be recombined with a signal (such as a television signal) from which the input noise signal for the invention was originally extracted. In a preferred embodiment, the input noise signal supplied to the system of the invention is generated by subtracting two adjacent frames of a television signal.

Abstract: A radio receiver circuit which suppresses an interfering signal exhibiting an amplitude significantly greater than that of a desired signal and a frequency nearly the same as that of the desired signal is disclosed. A received signal is applied to a gain controlled amplifier and a limiter. The limiter provides a limited signal which reduces amplitude and power of the desired signal relative to the interfering signal. The gain controlled amplifier provides a constant amplitude signal at an amplitude where the interfering signal portion of the constant amplitude signal equals an amplitude of the interfering signal portion of the limited signal. The constant amplitude and limited signals combine through a subtraction operation resulting in a significant attenuation of the interfering signal while causing only a small attenuation of the desired signal. Switching and decision circuitry are provided to selectively utilize the interference suppression.

Abstract: Strong narrowband signals interfering with the reception of a desired broadband signal in systems such as spread spectrum systems are continuously suppressed by converting the received signal to a frequency-domain representation thereof wherein strong narrowband interference components appear as strong impulse components. These impulsive components are blanked or clipped at a level that is a function of the average magnitude of the input signal. Resulting suppressed frequency-domain signals are reconverted to time-domain signals that are then available for further processing by conventional broadband signal receivers.

Abstract: An intermodulation distortion reducing circuit for a frequency-modulated signal comprises a sinusoidal wave shaping circuit supplied with an input frequency-modulated signal including an intermodulation distortion component, for shaping the waveform of the input frequency-modulated signal into a waveform closely approximating a sinusoidal wave, and a mean DC level detecting circuit supplied with an output signal of the sinusoidal wave shaping circuit, for detecting a mean DC level of the output signal of the sinusoidal wave shaping circuit and producing a detection output. The sinusoidal wave shaping circuit is supplied with the detection output of the mean DC level detecting circuit and a waveform shaping quantity thereof is varied to obtain the waveform closely approximating the sinusoidal waveform. The sinusoidal wave shaping circuit produces a frequency-modulated signal having a waveform closely approximating a sinusoidal waveform, with its intermodulation distortion component reduced.

Abstract: A floating limiter circuit for reducing interference from high frequency, very large pulses or fast rise time pulses, without distorting the desired signal. The reference voltage for the limiter circuit is established by the envelope of the desired output signal, thereby allowing the desired signal to vary over a wide dynamic range.

Abstract: A method and apparatus for receiving and detecting pulsed RF signals within first frequency band. Incoming pulsed RF signals are supplied to a linear amplifier which amplifies any of the signals within a broader second frequency band. The pulsed RF output signals of the amplifier are supplied to an in-band signal detection circuit controlling switches in the outputs of a first video detector and a frequency discriminator which are also supplied with the amplifier output signals, so that output video and frequency signals are provided only for pulsed RF signals within the first frequency band.

Abstract: An AM stereo receiver for receiving AM stereo broadcasting of an AM-PM or AM-FM system. Between an IF AM signal amplifier and an limiter is interposed a 5 or more frequency multiplier so that the frequency of a spurious signal radiated from the limiter may lie outside of the frequency range handled by the RF tuner.

Abstract: A single sideband receiver translates the frequencies of a received signal composed of a data signal and a pilot tone to predetermined intermediate frequencies. Filters separate the intermediate frequency data signal and the intermediate frequency pilot tone. The frequency of the intermediate frequency pilot tone is translated to a frequency sufficiently removed from the frequency spectrum of the intermediate frequency data signal so as not to interfere therewith. The translated, intermediate frequency, pilot tone and the intermediate frequency data signal are amplified by a single automatic gain controlled amplifier. A demodulator produces audio output signals and a recovered pilot tune in response to the output signal of the amplifier. The recovered pilot tone is input to a pilot regenerator. The output signal of the pilot regenerator is input to the demodulator. The recovered pilot tone is also input to an automatic gain control circuit.

Abstract: A spread spectrum detector utilizes compressive receiver techniques and squaring of the incoming signal to detect the presence of a spread spectrum signal and to obtain its center frequency, with the squaring cancelling the pseudo-random code. Once having determined the center frequency, the gated output of the compressive receiver's dispersive delay line may be directly demodulated without resort to code correlation, by applying the output of the dispersive delay line to a narrowband filter set to the detected center frequency. Narrowband interfering signals are rejected by a continuous comb filter, hard limiters for the filter outputs and a summing device. The same narrowband signal rejection can be accomplished by hard limiting the output of the compressive receiver delay line and then returning to the time domain with an additional dispersive delay line having a dispersive characteristic inverse to that of the compressive receiver delay line.

Abstract: A limiter circuit comprises a low-pass filter which passes only a modulation signal out of the modulation signal having pulsive noises superimposed thereon and circuit means for supplying the modulation signal extracted by the filter to current source circuits for a limiter differential amplifier to control the current source circuit for the limiter differential amplifier in accordance with a waveform of the input modulation signal applied thereto.