Abstract: A demodulator receives a radio signal and causes a carrier signal reproducing circuit to reproduce the carrier signal of the received signal. One amplifier amplifies the amplitude of the reproduced carrier signal by K, and another amplifies the amplitude of the reproduced carrier signal by (K+2). An adder adds the reproduced carrier signal, amplified by K, and the received signal. A subtracter subtracts the received signal from the reproduced carrier signal amplified by (K+2). The output signal of the adder is demodulated by a first FM demodulator and the output signal of the subtracter is demodulated by a second FM demodulator. Another subtracter outputs the difference between the demodulated signals from the first and second FM demodulators as a demodulated signal of the received signal.

Abstract: An improved modulator circuit for mixing a modulation signal with a carrier signal includes first and second harmonic mixers which are operative to produce modulated output signals at an output frequency corresponding to both the sum and the difference of the modulation signal frequency and the even harmonic frequencies of the carrier signal frequency. In one configuration employing a 90.degree. hybrid, the output signals of the harmonic mixers are combined to produce a single sideband modulated output signal. A novel harmonic mixer circuit is also provided along with demodulator circuits and methods of modulating and demodulating modulation signals.

Abstract: A sideband receiver that locks to a pilot component of a received signal. The pilot component is down-converted and then up-converted prior to phase comparing the pilot component information to provide a lock function. The receiver architecture allows monolithic integration of the receiver on a single integrated circuit (401).

Abstract: SSB receivers which use feedback and feedforward automatic gain control (AGC) are subject to bursts of noise in the audio output due to the action of the feedforward AGC when signals having low signal to noise (S/N) ratios are being received. This invention minimizes such noise bursts by disabling the feedforward AGC at a predetermined threshold S/N ratio independent of the feedback AGC control voltage. Noise within the received channel is bandpass filtered and a first signal generated which has an amplitude proportional to the filtered noise. The first signal is compared with a reference voltage which corresponds to the threshold at which the feedforward AGC is disabled.

Abstract: A system and method for detecting the level of random noise contained in a band-limited amplitude-modulated signal. A sychronizing signal is produced which is .pi./2 out of phase with respect to the carrier of the amplitude-modulated signal. The amplitude-modulated signal and the synchronizing signal are multiplied together. Only a low frequency component is extracted from the multiplication output, and the low frequency component is taken as an indication of the level of the random noise contained in the amplitude-modulated signal.

Abstract: A compressed single side band communication system and method in which the audio signal is compressed prior to pre-emphasis and thereafter summed with a pilot tone for further compression prior to transmission. Initially, only the pilot tone is transmitted at full rated power to aid in acquisition of the signal by the receiver. Thereafter, the transmitter ALC is disabled and the pilot tone is attenuated. The receiver adjusts the frequency characteristics of the pilot tone filter and phase lock loop filter in the detector as a function of lock-on. The delay after loss of lock-on in reverting to wide band pilot tone and wideband loop filters is varied as a function of signal strength. The pilot tone may be frequency modulated for tone coded squelch, with the modulating source being located in the return end of the phase lock loop filter. A unique filter is provided to insure acquisition of the pilot tone.

Abstract: A frequency control circuit for a single sideband receiver is disclosed wherein the local oscillator is swept at a first rate to enable the acquisition of a transmitted signal. When the signal is acquired, the local oscillator is swept at a second rate in an indicated direction in order to center the signal. Upon centering, the local oscillator is maintained at a frequency which centers the signal in response to the activation of a squelch detector.

Abstract: An automatic frequency control circuit for a single side band receiver employing a split-loop phase locked loop system is disclosed. Initially, both a first and second voltage controlled oscillator lock to a received pilot taken after the IF strip of the SSB receiver. Once lock is achieved, a sample is taken of the control line voltage of the first VCO whereafter the first VCO control line is held at the sampled voltage and will no longer track the received pilot until such time as the second VCO deviates from a predetermined range. Simultaneous to switching the first VCO, the loop filter of the second VCO is adapted to maintain identical loop dynamics both before and after switching control of the first VCO.

Abstract: A compressed single side band communication system and method in which the audio signal is compressed prior to pre-emphasis and thereafter summed with a pilot tone for further compression prior to transmission. Initially, only the pilot tone is transmitted at full rated power to aid in acquisition of the signal by the receiver. Thereafter, the transmitter ALC is disabled and the pilot tone is attenuated. The receiver adjusts the frequency characteristics of the pilot tone filter and phase lock loop filter in the detector as a function of lock-on. The delay after loss of lock-on in reverting to wide band pilot tone and wideband loop filters is varied as a function of signal strength. The pilot tone may be modulated for tone coded squelch. The modulating source is located in the return end of the phase lock loop filter. A unique filter is provided to insure acquisition of the pilot tone.

Abstract: A transmitted signal includes a pilot signal at a given frequency and an information signal occupying a different band of frequencies. A noise reduction system for a signal receiver detects modulation on the pilot signal and generates a signal having a frequency that varies in response to the detected modulation. The system includes an apparatus for combining the received signal with the generated signal to produce a signal at another frequency with reduced frequency noise.

Abstract: A compressed single side band communication system and method in which the audio signal is compressed prior to pre-emphasis and thereafter summed with a pilot tone for further compression prior to transmission. Initally, only the pilot tone is transmitted at full rated power to aid in acquisition of the signal by the receiver. Thereafter, the transmitter ALC is disabled and the pilot tone is attenuated. The receiver adjusts the frequency characteristics of the pilot tone filter and phase lock loop filter in the detector as a function of lock-on. The delay after loss of lock-on in reverting to wide band pilot tone and wideband loop filters is varied as a function of signal strength. The pilot tone may be modulated for tone coded squelch. The modulating source is located in the return end of the phase lock loop filter. A unique filter is provided to insure acquisition of the pilot tone.

Abstract: A single carrier is amplitude-modulated by a signal which is a transform (as the sine function) of the audio signal, and one set of sidebands is removed. In a receiver, the signal can be recovered by first deriving the Hilbert transform of the sine transform, and multiplying it by the signum of the derivative of the original audio signal to obtain the cosine transform. The sine and cosine transforms are then decoded to obtain the original audio signal.

Abstract: The present invention relates to a frequency-hopped single sideband (SSB) mobile radio system implemented by hopping the carrier frequency of an input signal (s(t)) every .tau. seconds. The hopping is controlled by a carrier-frequency-hopped sequence (f.sub.i (t)) generated by a carrier-frequency-hopping generator (16,24). When employed in a frequency-hopped SSB transmitter (10), the carrier sequence functions to modulate the input signal, "hopping" it to a different carrier frequency every .tau. seconds. The carrier-frequency-hopped SSB receiver (20) employs the identical carrier sequence as used by the transmitter to demodulate the transmitted carrier-frequency-hopped SSB signal, thereby recovering the original single sideband signal (s(t)). By frequency hopping the carrier signal of an SSB signal, the present invention mitigates the effects of co-channel interference and frequency selective fading inherent in prior art SSB cellular mobile radio systems.

Abstract: In a single sideband radio receiver utilizing a limited, pilot-controlled, gain correction arrangement (38) to compensate for radio channel fading, a signal (RECT CAP) representing receiver audio output level is utilized (97) during intersyllabic quiet intervals to increase the limiting threshold on the gain correction signal to suppress noise and interference.

Abstract: A receiver for demodulating a single sideband signal which is subject to rapid phase jitter employs a Hilbert splitter for obtaining the Hilbert transform of the single sideband signal, and a local oscillator for signal demodulation. A post-oscillator feedback loop instantaneously derives the amount of phase jitter in the single sideband signal, and employs the derived phase jitter to adjust the phase of the local oscillator so that the local oscillator tracks the single sideband signal.Instantaneous derivation of the phase jitter is obtained because all post-oscillator signal manipulations are algebraic; post-oscillator Hilbert transform generation is not required. A first embodiment derives the exact amount of phase jitter. A second embodiment, more simple than the first, derives the approximate amount of phase jitter.

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 frequency conversion system, including a time shared frequency converter and a time shared band limited amplification system, whereby a plurality of information bearing signals are commonly obtained, determined, filtered and amplified over a single path. The process admits signals whose carriers are separated by frequency or phase, and whose amplitudes are different.Synchronous and asynchronous receivers which ordinarily require dual mixers, filters and amplifiers are simplified by this invention. Phase locked loop demodulators, including AM, DSSC and Costas loop demodulators, which ordinarily require a pair of phase detectors, filters and amplifiers to generate the in-phase and quadrature-phase channels are simplified by this invention. The use of a common path for the in-phase and quadrature-phase channels also permits the close matching of gain and frequency response in each channel.

Abstract: Effects of multipath fading and Doppler frequency spread in a single sideband radio communication system are largely overcome by separating (17) from a received signal spectrum, a pilot frequency component including those effects and using that component to accomplish both phase (36) and gain (38) corrections on an information-containing frequency component. Signals essentially free of those effects are provided (10) for controlling necessary frequency translations in the receiver. One illustrative embodiment (FIG. 4) is conveniently arranged for facilitating diversity signal combining.

Abstract: Automatic frequency control (afc) particularly for single sideband (SSB) receiving systems.In a SSB receiving system, fine tuning is carried out using an afc loop. In one embodiment the loop includes a frequency discriminator for measuring the frequency of a composite i.f. signal (pilot carrier and modulating signal) and producing a waveform having an amplitude corresponding to the measured frequency. The amplitude waveform comprises the pilot carrier interspersed by the modulating signal. The frequency of the pilot carrier is measured using a peak detecting circuit and this measurement is used to automatically fine tune the receiver.

Abstract: A single sideband receiver having a demodulator or mixer for carrier frequency demodulation in response to the output of a controllable variable frequency oscillator and an intermediate frequency demodulator for providing a demodulated signal is provided with an automatic frequency control system comprising a low pass filter for separating a low frequency portion from the demodulated signal a discriminator for detecting the level of the low frequency portion with respect to a predetermined level, and a circuit for controlling the frequency of the variable frequency oscillator in response to the detected relationship between the low frequency portion and the predetermined level.

Abstract: The invention relates to an AM-receiver for receiving one of the sidebands of a double sideband signal, for example, in medium wave or short wave broadcast. Selective fading is avoided by the reception of one sideband only. The circuit can substantially be implemented from input to output in integrated circuit technology. It enables the high-grade reception of the double sideband AM-signals without crosstalk or squal.