Abstract: A system and method for in-service transmitter phase noise measurements determines phase nonlinearity by way of comparing unfiltered signal samples and regenerated reference signal samples to calculate phase nonlinearity error. Linear distortion is removed from the received signal samples in order to truly characterize nonlinear behavior of the transmitter. The unfiltered signal samples are generated without applying the receiver shaping filtering. Reference signal samples are regenerated from estimated transmitted symbols derived from the unfiltered signal samples. The transmitted symbols are estimated using a segmented slicer which dynamically estimates constellation decision levels from the unfiltered signal samples. A weighted, least-square based polynomial regression is performed on phase error samples of the unfiltered signal samples to estimate a phase nonlinear error function while suppressing the impact of other non-systematic distortions.

Abstract: An in-service composite triple beats (CTB) measurement system for a cable television (CATV) system isolates and measures weak composite triple beat components in the presence of a visual carrier modulated with program material for selected channels of the CATV system. Each channel is demodulated and digitized in a frequency bandwidth about the visual carrier for the channel (the CTB frequency range). The digitized video is sampled during the vertical interval, and corresponding samples from consecutive frames are differenced, squared and accumulated to produce a CTB value, which may be scaled and corrected for noise. Noise correction is achieved by performing the same measurement, but digitizing in a frequency bandwidth offset from the CTB frequency range. The difference between the two measurements provides a corrected CTB value.

Abstract: A spectrum analyzer (50) has a tunable trigger acquisition system (52) that includes a selectable trigger acquisition bandwidth. Sufficiently wide signal acquisition bandwidth is obtained by tapping into a high-frequency IF amplifier (54) signal and down-converting it to a moderate IF frequency for trigger extraction. A down-conversion local oscillator (62) is phase-lock-loop (64) tunable over a range of the high IF frequencies to allow extracting a time and frequency selectable trigger from the desired carrier signal frequency even if the spectrum analyzer is substantially offset in frequency from the desired carrier. The moderate frequency IF amplifier (66) includes a switchable bandpass filter (68) that provides adequate selectivity to detect triggers from a variety of signal types while rejecting unwanted signals such as adjacent channel CATV carriers that are often detectable when the measurement frequency is offset toward the channel edges.

Abstract: A liquid crystal light valve (10) includes compensation for wire shadow effects caused by the interception of writing beam primary electrons as they propagate through the collector electrode (66). The wire shadows stem from the lack of charge deposited on target surface regions ( 106) intended to be addressed by the writing electron beam (60a). The present invention applies to the collector electrode an appropriate voltage that diverts the paths (112) of nonintercepted writing beam electrons toward target surface regions directly below the collector electrode portions that intercepted the writing beam electrons. Diverting the paths of nonintercepted electrons provides a more uniform charge distribution on the target surface (45) and thereby fills the charge voids created by the electron intercepting portions of the collector electrode.

Abstract: An electrical circuit compensates for spatial variations in the light transmittance of the target surface (45) of an electron beam-addressed liquid crystal light valve (10). Such variations in light transmittance, which stem in part from the position dependent angle of incidence of the writing beam electrons and position dependent alignment layer variations arising out of manufacturing process limitations, affect the ability to achieve a monotonic gray scale luminance over the display surface. The compensating circuit adjusts the amount of beam current of the writing electron beam by varying the gain and offset voltage of the video signal, which modulates the writing beam current. This is accomplished by applying the X and Y scan position signals to a correction signal generator (102), which produces gain correction and offset correction signals whose magnitudes vary in response to instantaneous scan position of the writing electron beam on the target surface of a particular light valve.