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output as a passive low-pass filter. The network is easily designed 

 for 3 dB attenuation at 50 cycles per second with the aim of 

 eliminating 60 hertz noise from the power supply and local electrical 

 systems. Such high frequency noise would alias into the calculated 

 water wave spectra and bias the analysis results. An active filter 

 is, however, more strongly recommended. To guard against the 

 possibility of unwanted output oscillation caused by the capacitance 

 introduced by the long cable to shore, 100 ohm resistors are 

 installed in series in each of the output leads inside the 

 water-tight cylinder. Since the electrical circuitry of the 

 transducers is equivalent to a 4-terminal network which can be 

 grounded at only one point, it is essential that the negative output 

 leads of the transducers not be commoned since the negative 

 excitation leads are already commoned inside the instrument. 



A complete wiring diagram is presented in Figure III-8. 



8. The Instrument Cradle 



Both the instrument and the service box are mounted onto a 

 steel cradle secured to the seabed. The cable is constructed of 

 C4x5.4 steel channel and 3/A inch thick steel plate, two inch steel 

 pipe legs and Llxlxl/8 angle iron stringers. The channel is 

 connected primarily by the steel plate. A break is made in one plate 

 to allow the cable to slip through the structure when the instrument 

 is pulled out of the cradle. This is closed by a plate which bolts 



