| 摘要 |
A pulse-echo instrument wherein a balanced modulator is d.c. biased to pass a.c. signals is coupled between the transducer and wide-band amplifier of the instrument. The balanced modulator is also biased by a rectangular pulse having the amplitude and width of the excitation pulse applied to a transducer and the input of the balanced modulator, but of opposite polarity to the d.c. bias. This rectangular pulse is applied to the balance modulator coincidentally with the excitation pulse whereby the output of the balanced modulator is held at ground optential for the duration of the excitation pulse thereby preventing current flow in the output of the balanced modulator during the duration of the excitation pulse whereby paralysis of the wide-band amplifier by the excitation pulse is prevented.
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