166 Lecture 10 
In the earlier experiments, both amplitude and phase of received signals were 
recorded using a two-gun CRO. Figure 10.6 shows the circuits used (a) for con- 
tinuous wave and pulse transmission, and (b) for amplitude and phase recording 
of the received signal. In the case of the phase recording, the time base on the 
Y axis is synchronized with the transmitted signal and appears as a line of bright 
spots spaced one cycle apart whose vertical position indicates the phase of the 
received signal with respect to the transmitted signal. When only amplitude 
recording is required, a Bruel and Kjaer logarithmic (db) recorder has been used 
as well as the CRO. 
10.2, EXPERIMENTAL —° POINT-BY-POINT” METHOD 
With the transmitter emitting continuous waves at a chosen fixed depth and 
position in the tank, oscillographic records were made showing the variation of 
pressure amplitude when the receiver was moved slowly at constant velocity from 
the bottom to the surface of the water, the records being repeated at different 
ranges along the tank. In other experiments the variation of pressure amplitude 
was recorded as the range of the receiver was continuously decreased, the 
depths of transmitter and receiver being constant. These experiments indicated 
clearly that the sound distribution in the water showed a number of maxima and 
minima between surface and bottom, the spacing and amplitude of these varying 
in a somewhat irregular fashion and depending on a number of factors of more 
or less importance. The number of maxima between bottom and surface was 
clearly dependent on the directional properties of the transmitter and receiver, 
on the depth of the water, the wavelength of the sound, and on the nature of the 
bottom. It was also modified by waves on the water surface and by temperature 
gradients. 
SURFACE OF 
WATER 
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KX OOK 
PX OO 
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BP : 
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TIME @ © 3 1m @ zouns @ tincws @ akwours © siroves @ sinovss GarersowaG weswes (Oreos r20e0 (Drenes sisens 
Fig. 10.7. Pressure-amplitude records for constancy tests showing records of received signal as recei- 
ver is raised slowly from bottom to surface of water. 
