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Posted on Feb 5, 2014

The receiving systems used with the scanning type of echo-ranging equipments are of the dual-channel type, which is required in present methods of video portrayal. Deviation indicators, which are cathode-ray tubes or galvanometers, use either a sum-and-difference or a comparison receiving system. These systems are used to measure the phase angle o


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f the echo signal between the two halves of a transducer that has been electrically split so that, on reception, it acts as two independent hydrophones. When the proper circuits are used with these systems the phase angle can be translated into voltage differences, and the video portrayal is indicative of the deviation from the correct target bearing, that isodepression deviation indication (DDI) or bearing deviation indication (BDI). Scanning systems use conventional superheterodyne receivers-one for the video channel and one for the audio channel. The only function of the receiver in the video portrayal is to furnish brightening voltage to the grid of the cathode-ray tube because the scanning and deflection voltages are developed outside the receiver circuits. The audio channels are used to supply the returning echoes to the operator as an aid in identifying targets. The transducer used with scanning systems is keg-shaped and is mechanically and electrically divided into an even number of independent elements. In the model QHB-1 there are 48 such elements located so that each element covers an arc of 7 ½ ° of the transducer`s periphery. On transmission, the keying relay connects all the elements in parallel so that sound power is radiated in all directions simultaneously, whereas on reception the elements are connected so as to form a sharp beam in the horizontal plane. The output of each element is connected through its...




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