720 
2 Dy 
longer time intervals were required, longer lengths of copper tubes wore uscd. 
These copper tubes stood up well with the normal handling on the RELIANCE but 
they did "wear out" with time (that is after they had been in use for con= 
siderable periods of time they gave larger spurious signals when struck by 
a shock wave). Between the end of the copper tubes and the recording equip— 
ment it was satisfactory to employ commercial shiclded cable, such as micro— 
phone cable or Army-Navy type RG-l1/U, since the shock wave did not strike 
this cable until after the desired signal had been recorded. 
(ii) Frequency response of cables. In addition to the aistortion of 
the signal due to the finite size of the gauge and to cable signal, further 
distortion may be caused by lack of lincar frequency rcsponse. This may be 
due either to impedance mismatch between the cable and gauge or cable and 
oscilloscope, or to the dielectric absorption of the cable. Both of these 
difficulties can be overcome by the use of the proper terminating networks 
at the end of the cable []. 
For the early work done on the RELIANCE (previous to shot RE~125) the 
cables were compensated by a resistance=capacitance—inductance network at 
the input to the amplifiers of the cathode-ray oscilloscope (Fig. 9). 
This compensation circuit is familiarly reforred to as "single-ended" 
compensation, After shot RE~136, "double=ended" compensation was uscd. 
For this a resistance-capacitance network is placed at the input of the 
cathode=-ray oscilloscope and also at the far end of the cable as shovm in 
Fige 10. With the double-ended system of compensation the steady-state 
response of the cable is flat within + 3 percent up to 100 ke/see and the 
rise time for a step—impulse input is 2/;sec and the overshoot not more 
than 3 or ) percent compared to the step height at 1 mscc. 
The compensating network at the far end of the cables is inserted in 
the form of a small patch cord between the cables leading up to the surface 
and the 600-ft surface cables leading back to the RELIANCE, These units 
were suject to frequent failure from mechanical stress until the type of 
construction shown in Fig. 11 was adopted. These patch cords for the dif- 
ferent cables were all interchangeable, so that in case of failure they 
could be quickly replaced with a spare patch cord. The compensating net- 
work at the oscilloscope end of the cable was located at the input to the 
master control panel, These networks were also identical and wore of the 
plug-in type, so that one network could be quickly removed and another one 
plugged in. The condenser in the lattjcr network also served as the stand— 
ard condenser for the Q-calibrations. 
(c) Recording equipment, — After the signal had been brought to the 
recording vessel, it was necessary to make a permanent record of the trane 
sient voltage produced by the shock wave crossing the gauge. Cathode-ray 
oscilloscopes were uscd with photographic recording for this purposc. 
Associate equipment involved voltage-step sources for calibrating amplifier 
Soo RN a EEE AEE RTS eS 
2"See Secs 7(cv). 
