Abstract: A narrow band CW FM fixed height altimeter system utilizing linear Bessel function signal processing wherein a J.sub.0 and a J.sub.1 Bessel function signal component are compared in a biased comparator to yield an output signal at a predetermined, relatively low altitude. The system provides a very small, accurate, low cost solution to the problem of identifying a very low and predetermined altitude.

Abstract: A remotely situated detonator is acoustically triggered to detonate explosives. Conduit means capable of propagating an acoustic wave is used to transmit a precoded acoustic wave signal from a transmitter to a receiver. The receiver is provided with means for converting the precoded acoustic wave signal to an electrical output signal to actuate the detonator and decoding means for discriminating against noise signals. For safety reasons, time delay means may be provided to delay generation of the acoustic wave signals until after a predetermined time period. The aforedescribed detonation system may be utilized to rejuvenate or activate subterranean petroleum, gas, geothermal steam, or water and the like.

Abstract: A remotely situated detonator is acoustically triggered to detonate explosives. Conduit means capable of propagating an acoustic wave is used to transmit a precoded acoustic wave signal from a transmitter to a receiver. The receiver is provided with means for converting the precoded acoustic wave signal to an electrical output signal to actuate the detonator and decoding means for discriminating against noise signals. For safety reasons, time delay means may be provided to delay generation of the acoustic wave signals until after a predetermined time period. The aforedescribed detonation system may be utilized to rejuvenate or activate subterranean petroleum, gas, geothermal steam, or water and the like.