| 摘要 |
PURPOSE:To facilitate a decision on the bottom material by an underwater object detector, such as a fish finder, by decreasing its gain automatically to some extent where the decision on the bottom material is made, and performing recording up to the sea bottom, i.e. intermediate fish school recording normally and recording from the sea bottom with less density. CONSTITUTION:A transmission part 1 generates transmitted pulses P at a specific period and when a transmitter and receiver 3 is driven through a transmission-reception combining circuit 2, an ultrasonic wave is transmitted periodically and its reflected wave is amplified and sent to a gain switch 5. The output of the gain switch 5 is impressed to a sea bottom detector 7 after amplification 6 to generate a pulse when the reflected signal from the sea bottom arrives, and a time setting circuit 8 is driven by the pulse to generate an output which turns on for an adequately specified time, thereby impressing the output to the gain switch 5. The output of the time setting circuit 8 is impressed to the base of a transistor TR through a resistance R3 and then the TR turns on to connect the input side of the amplifier 6 through a resistance R2. Consequently, an input voltage to a power amplifier 9 drops and a voltage impressed to a recording pen 10 also drops to decrease the density of the recording of the sea bottom; and the light and shade in the record is easily discriminated to decide on the bottom material. |
