. Basic methods for the calibration of sonar equipment. EQUIPMENT AT MOUNTAIN LAKES 107 lull-scale deilcction on the recorder. I'he noise level under these conditions is oil the lower end of the recorder scale, which means that it is below 30 db vs 10-10 ^jitj i,^t„ 72 ohms. Recorder. The recorder circuit used in this system is practically identical with those of the lower fre- quency systems and operates only at 97 kc. Frequency-calibrated paper is available but onl\ for one relative speed of oscillator to recorder. How- ever, if it is necessary to make records at other speeds, calibrated tra
. Basic methods for the calibration of sonar equipment. EQUIPMENT AT MOUNTAIN LAKES 107 lull-scale deilcction on the recorder. I'he noise level under these conditions is oil the lower end of the recorder scale, which means that it is below 30 db vs 10-10 ^jitj i,^t„ 72 ohms. Recorder. The recorder circuit used in this system is practically identical with those of the lower fre- quency systems and operates only at 97 kc. Frequency-calibrated paper is available but onl\ for one relative speed of oscillator to recorder. How- ever, if it is necessary to make records at other speeds, calibrated transparent scales may be used. Indexing circuits for marking uncalibrated paper at predetermined points on the oscillator scale are available. Indexing, however, is done only when a special paper is being used, or when directivity pat- terns are being taken. Noise Generator. As shown in the block diagram, the noise generator may be substituted for the fixed oscillator at the entrance to the first buffer stage in the high-frequency system. The noise signal is a band centered at 15 mc and, as this is hetero- dyned with the variable-frequency oscillator, the re- sulting output is the same width centered at the frequency /. The random noise signal is first generated by a gas discharge tube (RCA 150-30), amplified and fed through a band-pass filter centeied at 455 kc. It is then used to modidate a signal from a crystal , and the products in the i)and cen- tered at mc are selected, doubled, and then tripled in frecpiency. Ihis gives as an output a band of noise kc wide, centered at 15 mc. The maximum signal level is approximately rms \olts across 72 ohms. The addition of a narrow band-pass filter and a local 455-kc oscillator in the noise generator makes it a very useful tool for accurately aligning the fixed- frequency oscillator at 15 mc. This is done by first adjusting the variable oscillator to one of the film scale calibration points
Size: 1399px × 1787px
Photo credit: © Library Book Collection / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookcollectionbiodiv, bookpublisherwashingtondc
