Abstract

An echo signal receiver receives higher level echo signals reflected from strong reflections sources or reflecting sources at areas close to a probe in a range of higher frequencies, and also receives lower level echo signals reflected from weak reflection sources or sources at areas remote from the probe in a range of low frequencies. The echo signal receiver comprises a multiple stage amplifier circuit for receiving the echo signal. Outputs from amplifiers at front stages are delivered via filters having higher frequency bands, and outputs from amplifiers at rear stages are delivered via filters having lower frequency bands. The outputs are passed through the filters and then combined into a single processed echo signal. As an alternative, a video signal derived from an echo signal which has passed through a circuit for varying frequency characteristics is compared with a reference voltage by a comparator, which produces an output that is rounded off by removing high frequency components in a low pass filter. The rounded off signal is fed to a circuit for varying frequency characteristics to control the same to change its frequency ban while the signal is being received. In another embodiment, the echo signal is received through a variable low cut filter having a cutoff frequency which can be increased or reduced dependent on the level of the echo signal.