Depth meter having improved time varying gain control

Claim 1

An improved depth sounder for detecting the depth of objects under the water comprising: a transducer for imparting sound pulses in response to electrical energization and in turn for providing an electrical signal output in response to reflected sound pulses; a resonant tank circuit having a transducer output-input connected to said transducer, a transmitting signal input, and a signal output; a voltage source having a positive pole and a negative pole; a time base circuit having a first, a second and a third NPN transistor each having a base, a collector and an emitter, the base of the first transistor being connected to the collector of the second transistor through a resistor, and the base of the second transistor being connected to the collector of the third transistor, the emitter of the first and second transistors being connected to the negative pole of said voltage source through a common resistor, the collectors of the first and second transistors being connected to the positive pole of said voltage source through separate resistors, the collector of the first transistor being connected to the base of the third transistor through a resistor, a capacitor connected across the collector-emitter junction of the third transistor, the emitter of the third transistor being connected to said voltage source negative pole and a resistor being connected between the third transistor base and said voltage source negative pole, the voltage signal appearing at the collector of said first transistor providing timing voltage signal of preselected pulse frequency, each pulse being of a preselected duration and the voltage signal appearing at the collector of the third transistor providing a ramp gain control signal at the same frequency as the timing voltage pulses; an oscillator circuit having an input connected to receive said time base circuit timing voltage signal and an output, the oscillator circuit providing time spaced bursts of electrical energy in response to energization by said time base circuit, the output of the oscillator circuit being connected to said resonAnt tank circuit transmitting signal input; a receiver amplifier circuit having an input, an output and a biasing signal input, the output of the amplifier being connected to said resonant tank circuit signal output; a metering circuit having a first input, a second input, the first input of the metering circuit being connected to said time base circuit output whereby each of said time spaced voltage pulses of said time base circuit initiates a measuring sequence in the metering circuit, the second input of the metering circuit being connected to said amplifier circuit output whereby signals received from said amplifier circuit in response to amplified signals generated by said transducer in response to receipt of sound pulses as an indication of the distance to the surface reflecting the sound pulses from said transducer, said amplifier circuit connected to receive said time base circuit gain control signal whereby said amplifier circuit has impressed thereon a time varying biasing voltage following each timing voltage signal pulse, such biasing voltage applied to said amplifier circuit serving to increase the amplification of said amplifier circuit with time whereby the signals resulting from reflective surfaces at greater distances from said transducer are amplified more than signals resulting from closer reflective surfaces.