Abstract: A transmitter includes a Loran pulse generator, a dispersion filter, an equalizer, a power amplifier, an antenna tuner, and an antenna. The Loran pulse generator is configured to generate a Loran pulse signal. The dispersion filter is coupled to the Loran pulse generator, and is configured to generate a dispersed signal responsive to the Loran pulse signal. The equalizer is coupled to the dispersion filter, and is configured to generate an equalized dispersed signal responsive to the dispersed signal. The power amplifier is coupled to the equalizer, and configured to generate an amplified signal responsive to the equalized dispersed signal. The antenna tuner is coupled to the power amplifier, and is configured to generate a tuned signal responsive to the amplified signal. The antenna is coupled to the antenna tuner, and is configured to radiate a transmitted signal responsive to the tuned signal.

Abstract: A digital television transmitter for an ATSC or NTSC signal includes a digital vestigial sideband modulator having a digital sinusoidal source. A digital multiplier arrangement multiplies a digital signal including the information in the digital television signal by a sequence derived by the digital sinusoidal source to derive plural orthogonally phased digital product signals. A digital lowpass filter arrangement passes low frequency components of the plural digital product signals and rejects high frequency components of the plural digital product signals. A signal combiner arrangement combines a carrier with signals containing information passed by the lowpass filter arrangement necessary to derive a vestigial sideband signal. The combiner arrangement includes at least one digital to analog converter that in different embodiments derives a vestigial sideband signal that modulates an I.F. or R.F. carrier.

Abstract: A reduced bandwidth 8VSB, ATSC transmitter transmits to conventional DTV receivers having bandpass filters with root raised cosine (RRC) band edge responses. The transmitter includes a vestigial sideband modulator for transferring energy in a portion of a spectrum on a first side of a predetermined frequency to a second side of the predetermined frequency. At the low band edge of the spectrum, the predetermined frequency is the pilot carrier frequency. At the high end of the spectrum, the predetermined frequency is the Nyquist sampling frequency. The energy transfer is such that no energy is transmitted between at least one band edge of the spectrum and an intermediate frequency between the band edge and the predetermined frequency. The energy is transferred on a frequency to frequency basis as a function of the energy in the RRC transition and the amplitude of a weighting function extending between the intermediate frequency and the predetermined frequency.

Abstract: An FM transmitter includes I and Q channels, each deriving a baseband sinusoidal wave having a frequency determined by speech and/or music broadcast information amplitude and nominally having the same maximum amplitude. Each wave drives a different balanced mixer, each responsive to orthogonally phased carrier waves. Outputs of the mixers are added to derive a frequency modulated output wave. The channels, mixers, and circuitry associated with them tend to introduce unwanted components in the output wave. Offset, peak amplitude, phase and relative delay of the added mixed outputs are such that the unwanted components are substantially eliminated from the output wave. The sinusoidal waves are derived by DACs responsive to signals derived by a digital processor having a memory storing amplitude vs. phase position values and slope vs. phase position values that are combined in response to samples of the broadcast information.

Abstract: An improved scrambler for serial digital video that is compatible with SMPTE Standard 259M inserts a detector/dithering circuit between the input serial digital signal and a scrambler. The scrambler's statistics are observed by a pair of up/down counters. One counter monitors the scrambled data prior to NRZI encoding to determine transition density, and the other monitors the NRZI encoder output to determine the relative density of "ones" and "zeros" in the scrambled output signal. A pseudorandom generator generates a dither signal which is combined with the least significant bit of selected video words of the input serial digital signal when enabled by the terminal count output from either counter. A complementary descrambler has a similar detector/dithering circuit at its output to restore the original least significant bit of the selected video words. The improved scrambler/descrambler may be implemented in either the serial or the parallel domain.

Abstract: An improved NRZ clock and data recovery system lends itself to integration, includes a NRZ phase detector, an NRZ frequency detector and a lock detector, and provides automatic centering of the clock edge within the bit interval in a manner that is independent of analog delays and process and temperature variations. NRZ data is applied to one side of an exclusive-OR gate and a twice delayed version of the NRZ data is applied to the other side. The output of the XOR gate, a "blivet" signal, is applied to a NRZ phase detector comprising two AND gates, one of which has as its other input a recovered clock signal output of a VCO and the other of which has as its other input an inverted version of the recovered clock signal. The "up" and "down" outputs of the AND gates indicate which direction a frequency control signal should change the VCO frequency. A data holding flip-flop whose input is a once delayed version of the NRZ data is clocked with the recovered clock signal.

Abstract: A multiple section cable equalizer with a signal level detector produces a clipping control signal for amplifiers in each equalizer section, so that a variable level input signal is restored to an equalized output signal that is free of distortion and attendant bit errors. A fixed reference clipping stage after the last equalizing stage produces a signal clipped to a final output level. A feedback path restores DC and low frequencies lost due to AC coupling. A test output stage permits monitoring of the operation of the equalizer stages. The signal level detector contains (in series), a differential amplifier with low pass filtering, a balanced modulator detector, a voltage amplifier, a comparator and peak detector, a transconductance amplifier and a plurality of current mirrors operatively connected to determine a difference current from the output of the transconductance amplifier and convert this to a clipping control signal voltage level.

Abstract: An analog "blue" signal detector detects when the amplitude of a spectral component of an input signal associated with a blue signal exceeds a given level for a predetermined period of time to provide an indication that the blue signal is present. When the blue signal is removed, the indication is rapidly removed also.

Abstract: A voltage controlled reference oscillator with a high Q and narrow tunability bandwidth produces an output oscillator frequency which is frequency divided by four alternative constants to produce four different clock frequencies for four different digital video standards, D1 component at 270 MHz, NTSC D2 composite at 143 MHz, PAL D2 composite at 177 MHz, and a proposed new composite video standard that is to operate at a 360 MHz clock rate. Automatic identification of which serial digital video is present is accomplished by having the clock generator produce a clock signal at the frequency required by one of the video formats while a phase lock loop attempts to lock onto the incoming signals at that frequency. If no lock occurs within a predetermined time interval, the clock generator is made to produce a clock signal at the frequency required by a different one of the video formats and the phase lock is attempted again. This is repeated until a lock is attained.

Abstract: A low jitter direct digital frequency synthesized frequency shift keyed modulator has a tapped delay line to provide polyphase sampling of an asynchronous data input signal. The samples from the tapped delay line are input to a correction signal generator that produces a correction signal as a function of the location of data transitions in the data input signal with respect to a specified point of a sample clock pulse. The correction signal is used to offset a modulating input to a direct digital frequency synthesizer so that the frequency shift keyed output reflects the data transitions within 1/n of the period of the sample clock pulse.

Abstract: An optical device compensator obtains from an input modulating signal an additive component and a multiplicative component. The additive and multiplicative components are combined with the input modulating signal to produce a compensated modulating signal which is applied to a driver for modulating an optical device.

Abstract: A numerical precorrection technique for modifying a digital signal corresponding to a desired analog signal to compensate for the characteristics of an analog filter which processes the digital signal after it is converted from digital to analog converts the digital signal into its spectral components. The spectral components are corrected according to the corresponding spectral characteristics of the analog filter for both amplitude and phase within the filter pass band and for phase only outside the filter pass band. The resulting corrected spectral components are converted into a corrected digital signal which is used to produce the desired analog signal.

Abstract: An AM stereo modulator is disclosed which includes a limiter responsive to first and second audio signals for providing first and second equally limited amplitude limited signals. A quadrature amplitude modulator responds to the first and second amplitude limited signals and provides an amplitude modulated carrier signal having in-phase and quadrature-phase components modulated in accordance with the first and second amplitude limited signals, respectively. A distortion detector monitors the envelope of the quadrature amplitude modulated signal for detecting the extent to which the envelope differs from one of the two amplitude limited signals and for controlling the limiter in accordance with the extent of the difference. The distortion detector can also be used to control quadrature channel signal gain instead of the limiter. A program analyzer determines whether to control quadrature channel signal gain or the limiter with the distortion detector.

Abstract: An AM stereo demodulator having monophonic and stereophonic modes of operation and adapted to demodulate a QAM signal whose quadrature-phase signal has a low frequency slot containing substantially no information signal therein. The demodulator includes a low-pass filter for filtering the quadrature-phase signal so as to provide a filtered signal containing only signals in the low frequency slot of the quadrature-phase signal. A window comparator compares the amplitude of the filtered signal with two threshold levels and provides a first output signal when the filtered signal is outside of the range bounded by the threshold levels. A circuit is included for placing the AM stereo demodulator in the monophonic mode of operation in response to the first output signal.

Abstract: Apparatus is disclosed for use in improving the separation between the individual channels of a plural channel communication system such as a stereo AM radio broadcasting system. The separation corrections are made to the baseband signals. Two sources (14, 16) provide input signals to a matrix circuit (18) which generates sum and difference signals therefrom. A circuit (44) adjusts the phase of the difference signal relative to the sum signal. The circuit (44) includes phase shifting circuits (50, 52) which provide two difference signals phase shifted by ninety degrees relative to one another. The two signals are combined in a signal adder (54). The degree of phase shift provided by the circuit (44) is selectively adjusted by varying the gain of gain circuits (46, 48) included in the paths of the two difference signals. Means (42, 44) are included for varying the gains of the input signals to the difference signal. The gain factors are frequency dependent in some embodiments.

Abstract: A receiver (12) including an asynchronous demodulator (28) for recovering program signals from a composite modulated signal (46) including in-phase (48) and quadrature-phase (50) components. A phase detector (52) provides a signal corresponding to the phase of the composite modulated signal, while an envelope detector (54) provides a signal corresponding to the envelope of the composite modulated signal. The quadrature-phase component is demodulated by multiplying the phase and envelope signals together in an analog multiplier (56). In one embodiment, this demodulated signal is distortion-corrected by combining it with a distortion correction signal. Circuitry (66, 68, 69) is also provided for using the envelope and phase signals to asynchronously demodulate the in-phase component of the composite modulated signal. A signal processing circuit (70) recovers the program signals from the in-phase and quadrature-phase modulating signals.

Abstract: A compatible AM stereo system employing a modified quadrature modulation scheme where the gain in the quadrature-phased channel, and thus the phase angle between the L and R modulated phase components of the composite modulated signal, is dynamically varied in accordance with changing modulation conditions. The average phase angle between the L and R modulated phase components is much greater than was previously possible in fixed gain systems, thus signal-to-noise ratio (SNR) in stereophonic receivers is improved. In the transmitter (FIGS. 3, 7A and 7B), a matrix circuit (40, 188) adds and subtracts L and R audio signals to produce sum (L+R) and difference (L-R) signals. An analog divider (54; 194, 200) adjusts the gain of the (L-R) signal in accordance with a gain control signal A.sub.Q. The (L+R) and gain adjusted (L-R) signals are transmitted on two quadrature-phased carriers by a quadrature AM (QAM) transmitter (50, 160). A distortion estimator (56, 190, FIGS.

Abstract: A compatible AM stereo system employing a modified quadrature modulation scheme where the gain in the quadrature-phased channel, and thus the phase angle between the L and R modulated phase components of the composite modulated signal, is dynamically varied in accordance with changing modulation conditions. The average phase angle between the L and R modulated phase components is much greater than was previously possible in fixed gain systems, thus signal-to-noise ratio (SNR) in stereophonic receivers is improved. In the transmitter (FIGS. 3, 7A and 7B), a matrix circuit (40, 188) adds and subtracts L and R audio signals to produce sum (L+R) and difference (L-R) signals. An analog divider (54; 194, 200) adjusts the gain of the (L-R) signal in accordance with a gain control signal A.sub.Q. The (L+R) and gain adjuster (L-R) signals are transmitted on two quadrature-phased carriers by a quadrature AM (QAM) transmitter (50, 160). A distortion estimator (56, 190, FIGS.

Abstract: A switching modulator (FIG. 3) for generating an FM composite stereo signal is disclosed. The modulator includes a switching circuit (40) for time division multiplexing the stereophonically related input signals onto an output line. The operation of the switching circuit is controlled by bilevel switching control signals provided by a function generator (48). The function generator provides bilevel switching control signals which have been modified so that the output of the switching circuit inherently lacks the third harmonic component which would have been present had conventional squarewave switching control signals instead been used. A low-pass filter (56) eliminates other, higher harmonics. A switching demodulator (FIG. 9) is also disclosed. This demodulator demodulates an FM composite signal through use of the same modified switching signal as used in the modulator.

Abstract: A filtering system for use in an FM modulating system. The filtering system provides frequency limiting of an input signal and does not overshoot amplitude limitations thereof. This filtering system includes a first filter and a second filter, separated by an overshoot compensator. The compensator modifies the output of the first filter in such a manner that, when the modified signal is filtered by the second filter, an output signal will be provided which does not overshoot a preselected amplitude. The overshoot compensator includes a threshold clipper which separates out any overshoot component generated by the first filter, an amplifier which amplifies the overshoot component, and a subtractor circuit which subtracts the amplified overshoot component from the output of the first filter to provide the modified signal. The second filter is of a type which provides a constant delay for all frequencies within the passband on the filtering system.