Communications – electrical: acoustic wave systems and devices – Wellbore telemetering – Through well fluids
Patent
1978-02-27
1980-07-29
Moskowitz, Nelson
Communications, electrical: acoustic wave systems and devices
Wellbore telemetering
Through well fluids
340853, 375 79, 375 83, G01V 140
Patent
active
042154251
ABSTRACT:
The disclosure is applicable for use in a logging-while-drilling apparatus for obtaining subsurface measurements during drilling in a fluid-filled borehole. Acoustic carrier waves are generated downhole in the borehole fluid and are PSK modulated in accordance with digital data representative of downhole measurements. The PSK modulation is obtained by momentarily unidirectionally either decreasing or increasing the frequency of the acoustic carrier signal until either a desired phase lag (for a decrease in frequency) or phase lead (for an increase in frequency) is imparted to the acoustic carrier signal. An uphole receiving subsystem includes transducers for converting the modulated acoustic carrier waves to electronic signals and circuitry for demodulating the electronic signals to recover the measurement information taken downhole. In accordance with an important feature of the invention, a filter is provided for selectively filtering the electronic signals before the demodulation thereof. The filter is provided with a bandpass characteristic having a center frequency which is displaced from the nominal frequency in the directon of the unidirectional decrease or increase of frequency applied when originally modulating the acoustic carrier waves. The center frequency is preferably offset from the nominal carrier frequency by an amount which is a function of the bit rate of the digital information, preferably an amount equal to one-half the bit rate of the digital information. In the preferred embodiment of the invention, the bandpass characteristic of the filter means is skewed in the same direction as the offset.
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patent: 3789355 (1974-01-01), Patton
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patent: 4065722 (1977-12-01), Francis
Huang, "Predistortion Equalization For PSK Modems," 6/77, pp. 154-158, IEEE Intern. Conf. on Communications, vol. 13, Chicago, Ill.
Gitlin et al. "Optimization of Digital . . . Detectors," 9/76, pp, 963-970, IEEE Trans on Conmun., Com 24, #9.
McMahon Kevin
Moskowitz Nelson
Sangamo Weston, Inc.
Sherman William R.
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