Abstract: Metal detector apparatus includes an increased pulse transmit frequency and reduced integration time constant for rapid target response and improved sensitivity to low conductivity metals, including cupro-nickel alloys, platinum and gold. Resistor-capacitor (RC) coupling totally eliminates the need to reset the controls due to changes in temperature or mineralization in the area being searched. The short time constant used in the RC coupling circuit improves the overall stability while reducing noise, allowing for greater amplification in the audio stages. The time constant of the RC coupling stage is equal or similar to the time constant of the integrator. The audio tone is derived from the pulse transmit clock which is synchronous with the power supply inverter to reduce noise and instability in the system.

Abstract: Echo ranging apparatus to locate fish, vegetation and structure in the sea modifies signals presented to a recorder in the apparatus so as to enhance the capability of the user to distinguish fish in the vicinity of vegetation and structure, including the sea bed. A transducer receives the reflected echo signals. A receiver stage and amplifier stage present signals which, apart from the modification, would be conventionally useful in aiding the user to locate fish. However, a signal modifier connected at the output of the amplifier stage, between the amplifier stage and the input to the recorder, substantially enhances the capability of the apparatus. It does so by shunting signal reducer circuitry in parallel at the output of the amplifier when the level at the output surpasses a predetermined level, to reduce the signal levels at such output while retaining variations in such signal levels. Such retention, as opposed to, e.g.