Bandwidth Signal Processing Research Articles

Real-time location of multiple time-varying strain disturbances, acting over a 40-km fiber section, using a novel dual-Sagnac interferometer

Updated results using a novel sensing architecture based on a Sagnac interferometer are presented and, for the first time, real-time separation and positioning of multiple disturbances has been realized. A 40-km long dual-Sagnac sensor was formed by spectral slicing of light from a single, broad-band erbium-doped-fiber super-luminescent source and wavelength division multiplexed (WDM) routing around the loop to form an inherently low loss system. Independent active phase biasing of each Sagnac was employed, allowing the use of a single optical detector. The effects of residual optical cross talk between the two Sagnacs has been accurately modeled, allowing resulting errors to be corrected. The new system has capability for narrow-band fast Fourier transform (FFT) analysis of detected disturbance signals, and hence their separation in the frequency domain. For audio-frequency excitation, an average positional resolution of 100 m over a 40-km length was achieved with a postdetection signal processing bandwidth of 8 Hz.

Application of High Temperature Superconductors in Passive Microwave Devices

The front end of a microwave communications system is assembled from circuit elements comprising antennae, local oscillator, mixer and filters. Interconnection is by transmission line, into which delay may be incorporated. All of these components can, with advantage, be implemented in superconducting material. Superconductors, when operating below their cross-over frequency, have values of surface resistance lower than those for normal metals such as copper and silver. This results in lower insertion loss for microwave components, allowing the design of smaller, more compact, yet at the same time more complicated, devices. The non-dispersive nature of superconductors can also be an advantage in enabling very high bandwidth signal processing. High temperature superconductors (HTS) allow operating temperatures in the liquid nitrogen range, not too far below the ambient temperature in many communications satellites. The Oxford microwave programme has concentrated on the implementation of all of the above devices in thin-film HTS, mainly Tl-2212, on a variety of substrates. The film fabrication, and performance of delay lines, antenna-mixers, resonators, filters and a voltage-controlled oscillator, are described.

Coherent optical QPSK intradyne system: concept and digital receiver realization

A receiver concept based on optical quadrature phase-shift keying (QPSK) and a digital realization of synchronous demodulation including phase synchronization is presented. To keep the signal processing bandwidth low a phase diversity receiver, called an intradyne receiver, with an orthogonal electrical demodulation is proposed. Basic principles of the synchronous orthogonal and digital demodulation are described. After the evaluation of the shot noise limit some aspects of the digital phase-locked loop (PLL) are presented. In a 100-Mb/s transmission system a receiver sensitivity of -51.6 dBm has been measured. The loss in relation to the shot noise limit of -66.3 dBm (18 photons/b) is mostly due to the low local laser power and the influence of the receiver input noise. >

Recommendations for standardization and specifications in automated electrocardiography: bandwidth and digital signal processing. A report for health professionals by an ad hoc writing group of the Committee on Electrocardiography and Cardiac Electrophysiology of the Council on Clinical Cardiology, American Heart Association.

Recommendations for standardization and specifications in automated electrocardiography: bandwidth and digital signal processing. A report for health professionals by an ad hoc writing group of the Committee on Electrocardiography and Cardiac Electrophysiology of the Council on Clinical Cardiology, American Heart Association.

Signal shaping and tail cancellation for gas proportional detectors at high counting rates

A low noise, wide bandwidth preamplifier and signal processing filter were developed for high counting rate proportional counters. The filter consists of a seven pole Gaussian integrator with symmetrical weighting function and continuously variable shaping time, τ s , of 8–50 ns (fwhm) preceded by a second order pole zero circuit which cancels the long (1/ t) tails of the chamber signals. The preamplifier is an optimized common base input design with 2 ns rise time and an equivalent noise input charge /lt 2000 r.m.s. electrons, when connected to a chamber with 10 pF capacitance and at a filtering time, τ s , of 10 ns.

Signal Shaping and Tail Cancellation for Gas Proportional Detectors at High Counting Rates

A low noise, wide bandwidth preamplifier and signal processing filter were developed for high counting rate proportional counters. The filter consists of an eight pole Gaussian integrator with symmetrical weighting function and continuously variable shaping time, ?s, of 8 ns to 50 ns (FWHM) preceded by a second order pole/zero circuit which cancels the long (1/t) tails of the chamber signals. The preamplifier is an optimized common base input design with 2 nsec rise time and an equivalent noise input charge of < 2000 rms electrons, when connected to a chamber with 10 pF capacitance and at a filtering time, ?s, of 10 ns.

The applications of lower power satellites for direct television broadcasting

The use of 12 GHz satellites for TV broadcasting directly to individual homes and small communities has been the subject of analysis and design study by groups in many countries. Implementation of the concept has been slow to follow because of the high satellite transmitter powers of from 100 to 450 W that have usually been determined to be necessary. Accumulated experience in Canada with 12 GHz operation and the evolution of technology are leading to changes in the concept of direct broadcasting such that lower power satellites may be capable of meeting the requirements. Hermes, the Canadian/U.S. 12 14 GHz Communications Technology Satellite, has been in use for over 3 years in a program of experiments and measurements. This program has included an extensive six month experiment in direct broadcasting to 7 small communities. Experience with Hermes has shown that the signal strength is stable over long periods of time and that in Canada, significant precipitation attenuation at 12 GHz is of relatively short duration and typically occurs only during certain seasons. Operation with low propagation margins is feasible if some picture degradation and some outages at these times are acceptable. The frequency and duration of occurrence of outages can be controlled by the Earth station G T which is cost sensitive. An individual may choose to use a low cost system with a small antenna and accept a degraded picture and outages at some times. A small community may choose to pay more for a larger antenna and lower noise receiver to achieve better performance. Developments in technology are reducing the noise figure of mass-producible receivers from more than 6 dB to as low as 4 dB. Another technology contribution is the use of reduced bandwidth and other signal processing techniques in low-cost receivers. While use of such techniques may introduce distortions that would be unacceptable in rebroadcasting systems, there is little impact for individual and community reception. Use of both technologies reduce the required satellite EIRP or ground terminal G T . A field trial was begun in April 1979 to test these concepts for use in television program delivery. One hundred Earth stations capable of being tuned across a 500 MHz band and having antennas with diameters of either 1.2 m or 1.8 m are being installed for a test in Canada to receive TV signals from the 20 W transponders of ANIK-B (peak EIRP of 51 dBw) on an experimental basis. The acceptability of the video signals and the technical performance of the low-cost terminals in the bands of non-technical users are being evaluated. The paper will summarize the concept of TV broadcasting with lower power satellites and describe the results to date of the ANIK-B field trials.