| 摘要 |
PURPOSE:To achieve an effective removal of background noise by subtracting only a specified value from a reflection digital signal during the period of gate signals which are generated rising in synchronization with transmission pulses. CONSTITUTION:Trigger pulses are applied to a variable gate signal generator 38 synchronizing transmission pulses from a receiver 12 and gate signals from the variable gate signal generator 38 are fed to a subtractor 17. While the gate signals are being inputted, the subtractor 17 subtracts a specified value, for example, 1 from output digital signals of an analog-digital converter 16 and the results are fed to a buffer memory 18. But when there are no such signals fed thereinto, the output of the analog-digital converter 16 is fed to the buffer memory 18 in stead. With a knob 39, the width of the gate signals is varied to adjust the range of background noises as desired. |
