. Basic methods for the calibration of sonar equipment. EQUIPMENT AT MOUNTAIN LAKES 71 Committee [NDRC]. The Undenvater Sound Refer- ence Laboratories ha\e designed and constructed most of tlie mechanical eiinipmeni anil have de\cl- oped the liigh-power et|ui|)meiu, the pidsing system, the polar recording system, and certain adtlitional featmes needed for special testing. .6!! CALIBRATION AND TESTING EQUIPMENT AT MOUNTAIN LAKES The calibration and testing systems of USRL are described on the basis of their present status. 11 should be emphasized. ho\\e\er. that dexelopments in sonar gear and t
. Basic methods for the calibration of sonar equipment. EQUIPMENT AT MOUNTAIN LAKES 71 Committee [NDRC]. The Undenvater Sound Refer- ence Laboratories ha\e designed and constructed most of tlie mechanical eiinipmeni anil have de\cl- oped the liigh-power et|ui|)meiu, the pidsing system, the polar recording system, and certain adtlitional featmes needed for special testing. .6!! CALIBRATION AND TESTING EQUIPMENT AT MOUNTAIN LAKES The calibration and testing systems of USRL are described on the basis of their present status. 11 should be emphasized. ho\\e\er. that dexelopments in sonar gear and the constantly improving tcchnicjues in test- ing are making new demands, in many cases beyond the capacities of existing etjuipment. It must there- fore be constantly changed and impro\ed to maintain the standards rec]iured of a reference laboratory. For example, system 1, installed in Jiuie 1942, in- corporated a narrow band-pass filter which discrimin- ated against noise and other interference. This was at the time a distinct improvement but after the de\el- opment of the pidse method, which requires a wider transmission band, system 1 was inadcciuate. For this reason, and also because of the increasing importance of noise analysis, system 1 is now limited in its appli- cations, and a continuously increasing proportion of the work is handled by system 2. Electrical Components of Systems The essential parts ol SNslems 1 and 2 arc descriijed in a sequence which traces a typical signal from the generator to the projector and from the hxdiophonc to the recorder. Test Signal Generators The primary signal generators are beat-frequency oscillators covering the 15-c to 15()-kc range with a re- sponse uniform within db. .\ visual indication of the frequency setting is ]3ro\ ided b\ a calibrated scale on a strip of 35-mm motion pictiue film 30 feet long, coupled through a sprocket chain to the air condenser controlling the frequency. The length of this scale in- dicates the d
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