Abstract: The number of simultaneous equations needed to find the location solution of an asset being tracked, such as a railcar, or, in the alternative, to improve the localization accuracy of any of several positioning methods used to track assets, is reduced by using a railway track database. Known railway track locations are used to constrain the railcar (i.e., asset) location solutions. This constraint makes the Cartesian coordinate location x, y and z values interdependent and reduces the number of simultaneous equations needed to find the location solution. Since all relevant railcars must be supported on railway tracks, and railway track locations and elevations throughout North America are available in a database, the number of satellite signals required is reduced. The railway track database represents a complex set of railway tracks.

Abstract: Correlation between a pair of digital signal segments is measured by apparatus including a plurality of multipliers. Each of the multipliers produces the product of a respective sample of each one of the signal segments. The outputs of a plurality of digital-to-analog (D/A) converters are coupled to a summer, while each respective one of the multipliers is coupled to the input of a respective one of the D/A converts. The summer produces an analog output signal equal to the sum of the analog output signals produced by the plurality of D/A converter.

Abstract: A phase splitter includes an input port coupled to receive a modulated carrier having a relatively wide bandwidth and has first and second output ports for supplying, respectively, first and second modulated carrier constituents having a uniform phase angle differential, such as 180.degree., between one another while maintaining a uniform amplitude over the bandwidth for the modulated carrier. A transmission line comprised of one or more individual segments includes first and second conductors respectively coupled to the output ports of the phase splitter to receive the first and second modulated carrier constituents from the phase splitter. A coupler is positioned sufficiently near the transmission line to receive the first and second modulated carrier constituents being applied to any of the individual segments.

Abstract: Location of an object to be tracked is determined by measuring, at a receiver situated at the object, the propagation time differences between the signals from a plurality of GPS satellites, each of which is received by the receiver situated at the object. The measured propagation time difference values are transmitted to a central station where the location of the object to be tracked is calculated based upon the propagation time differences of the signals transmitted from the satellites and data derived from a receiver apart from the object but also receiving signals from the satellites.

Abstract: Apparatus for reducing electromagnetic radiation from a differentially driven transmission line for high data rate communication in a computerized tomography system is provided. The apparatus comprises a carrier generator, for generating a carrier signal having a predetermined carrier bandwidth. A modulator is respectively coupled to the carrier generator for receiving the carrier signal and for receiving an externally-derived data signal to produce a modulated output signal. The carrier bandwidth is sufficiently broad relative to a predetermined inspection bandwidth for substantially reducing the level of electromagnetic energy being measured over the inspection bandwidth.

Abstract: A method of tracking railcars in transit using global positioning techniques involves determining the location of a railcar by using a Global Positioning System (GPS) receiver and a satellite transceiver on board the locomotive, and a local area network of railcar tracking units. Instead of computing the GPS solution independently and transmitting it to a central station, the railcar tracking units transmit their unique identifications (IDs) to one of the tracking units in the local area network acting as an administrator tracking unit. The administrator tracking unit maintains a list of IDs and periodically transmits the list of IDs to the locomotive. The locomotive locates itself using the GPS system and periodically transmits its position and velocity to the central station.

Abstract: Apparatus for reducing electromagnetic radiation from a differentially driven transmission line for high data rate communication in a computerized tomography system is provided. The apparatus includes a carrier generator to generate carrier signals having an adjustable phase shift angle between one another. The phase angle differential is selected to avoid formation of leakage signals due to misalignment occurring between the coupler and the transmission line during relative movement therebetween, thereby reducing electromagnetic radiation from the transmission line and the coupler.