Abstract: An apparatus for echo characterization or measurement includes a frequency domain adaptive filter for converging a plurality of filter coefficients based upon transmit and receive frequency domain transforms. The frequency domain adaptive filter preferably determines least mean square differences between estimated receive frequency domain transforms and the respective corresponding actual receive frequency domain transforms. The apparatus also preferably includes an echo characterization output portion for generating an echo characterization value for the communications channel. The echo characterization value may be one or both of echo path loss and echo delay. The apparatus preferably includes a gain normalization portion operatively connected to the adaptive filter for generating normalized gains of respective filter coefficients based upon spectral power of the respective transmit frequency domain transforms.

Abstract: A parametric echo canceller comprising two transversal filters is employed to recursively model the echo path. The first transversal filter receives the input signal, the fed-back echo residual signal and a first set of Kalman gain coefficients to produce a first intermediate result. The second transversal filter receives the echo signal, the fed-back echo residual signal and a second set of Kalman gain coefficients to produce a second intermediate result. The second intermediate result is subtracted from the first to yield an estimated echo replica. The estimated echo replica is then subtracted from the echo to yield an echo residual. The taps of the first and second transversal filters are weighted in accordance with first and second sets of weighting coefficients, which are generated in accordance with the Fast Kalman Algorithm.

Abstract: A gravity meter is formed by securing two parallel rods of different material at adjacent ends and indicating their differential elongation at the free ends. While capacitor, interferometer, and other devices could be used to measure this differential, the presently preferred indicator is a roller disposed between the free ends and the rotation due to differential elongation is indicated optically by a mirror attached to the roller. The indicator is zeroed while the rods are horizontal and the difference in elongation of the two rods is indicated when the rods are moved to a vertical position. The device may be moved over the earth's surface in the vertical position, while held at a constant temperature, to become a gravity meter.