588 
18 
single conductor cable with a surge impedance of 7/2 ohms. The frequency- 
response curve of this preamplifier and 500 feet of cable is essentially flat 
between 100 cycles per second and one megacycle per second. 
Another method consists in terminating the cable, at least approx- 
imately, in its surge impedance. This method has been described by Lampson 
(21). Other work has been done at the Taylor Model Basin on this problem 
(22). 
DISTORTIONS DUE TO MECHANICAL DISTURBANCE OF THE CABLE 
In Part 2 it was pointed out that the type of cable used with a 
gage is one of the factors which determine the degree of distortion of the 
signal obtained. In testing a piezoelectric gage at the Taylor Model Basin 
it was observed that mechanical disturbance of the cable modified the voltage 
signal perceptibly. It was evident that in using the gage to study the 
pressure-time variation near an underwater explosion, a spurious signal pro- 
duced in the cable could introduce an appreciable error. Preliminary tests 
confirmed this conjecture. A series of tests was undertaken to compare the 
voltage signals from various types of shielded, single-conductor cables ex- 
posed without other pickup to an underwater explosion. An attempt was then 
made to improve one of the best of these, a coaxial copper-tube cable, so as 
to reduce its distortion of a gage signal. Finally, certain relevant proper- 
ties of the modified cable were studied: The reproducibility of its voltage 
signal, and the effects of change in its orientation and configuration. 
Each cable under investigation was prepared for immersion by insu- 
lating the wire at one end, both from the concentric shield and from the wa- 
ter, by rubber tape coated with Bostik cement. The other end was connected 
to the input of an amplifier. The cable was then taped to a plank and low- 
ered diagonally into the water to a depth of 3 feet, as shown in Figure 9. 
Both cable and charge were mounted on suitable frames by means of which their 
depth and relative position could be accurately adjusted. 
A Number 8 detonator was exploded, and the voltage output of the 
cable as a function of time was recorded with a Du Mont Type 208 cathode-ray 
oscillograph and an auxiliary camera. The time axis on the cathode-ray 
screen was swept out by a TMB sweep generator, and synchronized with the ex- 
plosion by a trigger circuit. Voltage and time scales were calibrated with 
a Generel Radio Microvolter and an oscillator by impressing a sine wave of 
known emplitude and frequency on the screen of the cathode-ray tube. The 
photographic records were enlarged, and peak voltages were read off. 
A detailed description of the cables, including the capacitance of 
each, and a tabulation of the results will be found in Tables 1 and 2, re- 
spectively. The peak voltages generated by the different cables range from 
