| 摘要 |
<p>In an underwater digital communication system using acoustic signals, e.g. between a transducer station 12 and an underwater weapon system 10, successive digits of a message in serial form are sent using, for each digit, a selected sonic or ultrasonic frequency which differs from the frequency used for the preceding digit. Preferably three or four channels, the frequency selected for each digit being chosen according to whether the digit is a 0 or 1 and also differing from the frequency used for the preceding digit. By this technique, checking may readily be carried out to determine possible errors due to refraction effects in propagation through the water.</p> |
