Ehrman

Claim 1

FOR USE IN DETERMINING THE ALTITUDE OF THE HULL OF A HYDROFOIL CRAFT ABOVE THE WATER SURFACE, AN ULTRASONIC ALTIMETER MOUNTED ON THE CRAFT AND COMPRISING: A MAGNETOSTRICTIVE OSCILLATOR ORIENTED TO TRANSMIT ULTRASONIC ENERGY FROM THE CRAFT TOWARD THE WATER; A FREE-RUNING MULTIVIBRATOR HAVING A PULSE OUTPUT WHOSE PULSE WIDTH IS BRIEF COMPARED TO THE PERIOD AND WHOSE PULSE REPETITION RATE IS SLOW RELATIVE TO THE OSCILLATOR FREQUENCY; THYRATRON CIRCUITRY TRIGGERED BY THE MULTIVIBRATOR AND COUPLED TO THE MAGNETOSTRICTIVE OSCILLATOR THEREBY PRODUCING PULSES OF ALTERNATING ULTRASONIC ENERGY IN RESPONSE TO THE MULTIVIBRATOR PULSES; A MICROPHONE HAVING AN ULTRASONIC FREQUENCY RESPONSE, ORIENTED TO RECEIVE PULSES OF ULTRASONIC ENERGY REFLECTED FROM THE WATER; AN AMPLIFIER WITH AUTOMATIC GAIN CONTROL FOR AMPLIFYING THE MICROPHONE OUTPUT AND FOR MAINTAINING A CONSTANT OUTPUT SIGNAL LEVEL REGARDLESS OF THE STRENGTH OF THE REFLECTED PULSES; A PULSE DEMODULATOR FOR DEMODULATING THE AMPLIFIER OUTPUT; A GATED PULSE AMPLIFIER CONTROLLED BY A GATE GENERATOR TO BE RESPONSIVE TO DEMODULATED PULSES ONLY DURING THE TIME PERIOD BETWEEN SUCCESSIVE MULTIVIBRATOR PULSES; A FLIP-FLOP WHICH IS CONNECTED TO BE TURNED ON BY A PULSE FROM THE MULTIVIBRATOR AND TO BE TURNED OFF BY A GATED DEMODULATED PULSE PASSED BY THE GATED PULSE AMPLIFIER; MEANS FOR DIFFERENTIATING THE OFF OUTPUT OF THE FLIP-FLOP; A SAWTOOTH WAVEFORM GENERATOR WHOSE WAVEFORM PERIOD IS EQUAL TO THAT OF THE MULTIVIBRATOR AND WHOSE WAVEFORM AMPLITUDE IS LINEAR WITH TIME; MEANS FOR STORING A VOLTAGE LEVEL; A SAMPLING GATE CONTROLLED BY THE DIFFERENTIATION OFF OUTPUT OF THE FLIP-FLOP AND CONNECTED TO TRANSFER A SAMPLE OF THE SAWTOOTH WAVEFORM TO THE STORAGE MEANS; AND AN ANALOG-TO-DIGITAL CONVERTER RESPONSIVE TO THE STORED VOLTAGE LEVEL AND YIELDING A DIGITAL SIGNAL INDICATIVE OF THE ALTITUDE.