134 



ISRL TEST STATIONS 



more susceptible to noise and interference, but sev- 

 eral fixed filters are available to restrict the receiving 

 band when it is necessary to reduce the noise level.'' 



The linear recorder is of the same design as the one 

 on the pier. The polar recorder is synchro-controlled 

 from the rotator. The barge is also ecpiipped for pulse 

 testing with circuits which arc identical with those 

 at Mountain Lakes. The test-circuit cable from the 

 pier is carried on the surface by drums spaced at 

 various distances, while the power and communica- 

 tion cables rest on the lake bottom. 



When tests are to be made over greater distances 

 than the barge or pier areas permit, the distance is 

 extended by a small triangular float which can be 

 anchored anywhere in the lake and which is ecpiipped 

 with a simple hoist. 



<• This wide-band system was used because it was available at 

 llie time the barge was built, whereas the construction of a 

 heterodyne and filter system would have entailed considerable 

 delav. It may be noted that all the early testing systems of USRL 

 were of the wide-band type. 



e* RECXTMMENDATIONS FOR 



IMPROVEMENTS OF THE USRL 

 TEST STATIONS 



The recommendations made in this section will 

 deal mainly with improvements and additions that 

 may be made to the existing electrical and mechani- 

 cal components of the calibration systems. These 

 improvements and additions are of an immediate 

 practical nature and several are in the process of 

 development. The general purpose is to increase the 

 accuracy and ease with which the acoustic measure- 

 ments are made and the resultant data converted 

 into response, impedance, and other forms which 

 characterize transducers. (See Chapter 4.) 



General Improvements— Electrical 



Under proper operating conditions the stability 

 of the electric equipment now installed at USRL test 

 stations is approximately 0.1 db. Signal generators 

 are designed with very little drift in frequency. The 

 gain of each individual component is as uniform as 

 possible over the frequency range for which it is de- 

 signed. This is done so that the relation of gain to 



Figure 77. Attaching a line hydrophone to special sus- 

 pension rod on the Orlando barge. 



Figure 78. Part of the electrical s\stem on the Orlando 

 barge, including the linear recorder. 



