| 摘要 |
<p>Speed measurement error due to additive noise in the receivers of period-measuring doppler sonar apparatus is reduced by performing the period measurement process when and only when the signal is sufficiently strong. When the envelope of the received signal-plus-noise exceeds a preset threshold, a comparator output enables the initiation or the continuation of a doppler gate until N received periods have been counted. Typical logic, gating, counting and display circuitry is described which transforms this gate duration into an accurate indication of speed. Higher threshold levels can be established for increased accuracy at the expense of increased measurement time.</p> |
