Patent GB-1521366-A (GB)
Title: Seismic group recorder control system
IPC: H04L27/10
Filed: 1976-08-17
Abstract: 1521366 Seismic exploration STANDARD OIL CO 17 Aug 1976 [27 Aug 1975] 34228/76 Heading G1G In a cableless seismic digital recording system, small portable recorders using batteries with relatively short lifetimes are switched in and out of operation by radio remote control to maximize battery life e.g. as set out in Specification 1419458 (Division H3-5), the switching is provided by an improved communications system giving maximum range for turning on with accuracy a selected group of recorders and transmitting necessary recorded identifying information. As claimed there is a cableless seismic digital recording system using a plurality of portable seismic group recorders to record at selected time intervals the output of geophones located near said recorders, each such recorder being actuated by a limited energy source and possessing a receiver adapted for receiving high-frequency signals modulated by low-frequency signals from a control point Fig. 1 (not shown), remote from at least part of said recorders through a communication link, said receiver having a plurality of frequency-selective low-frequency circuits for channeling demodulated signals to control automatically the operation of said recorder, including selectively turning on only certain predetermined units of said recorders, actuation of recording medium motion by said source, recording digitally the output of geophones on said medium following recording of identifying header data, and turning off said recorder, wherein the system is adapted and arranged in operation to (a) modulate a high-frequency signal radiated from said control point only by blocks of substantially constant amplitude low monofrequency signals, Fig. 4, each block existing for a time T where T is constant and chosen such that each block contains an integral number of cycles of sine wave signals, plus one essentially continuous monofrequency timing wave, the frequency of each said block monofrequency being different from all others and related to the frequency of said timing wave by one being an integral multiple of the other, and all blocks being coherent, that is, each starting sinusoidally from zero in the same polarity using frequency-shift keying for said modulating;  (b) receive and demodulate said high-frequency signal at said recorders and filter the demodulated low-frequency signals in parallel through a plurality of filter channels (64-66), Fig. 3 (not shown), each tuned to one only of the monofrequencies of said blocks; (c) detect relative amplitudes of the electric output in said channels periodically and substantially at a time T in a plurality of predetermined combinations, each being sent automatically in accordance with each separate combination and the number of uninterrupted repetitions of said combination to a separate control circuit of said recorder, and (d) quench or dump all of said filter channels tuned to the frequencies of said block signals briefly, substantially simultaneously, and periodically at a time T, such time of quenching or dumping occurring just subsequent to the detecting step (c). The maximum contrast in output of the various filters (Fig. 4c) for an audio frequency coherent block of a particular frequency occurs as the quenching or dumping time T.