. Basic methods for the calibration of sonar equipment. AMPLIFIER RECORDER AND EQUALIZING I SYSTEM I SYNCHRONIZED RECORDING PEN EQUALIZING CHART. Figure 80. .Schematic diagram ot electromechanical equalizer. slant sound held o\ci ilic whole lne|iicncy range, or hydroplioncs which had a uiiilorm response for a consiaiu liild at all Iretiuciu ies, or both. Either in- slitimc'iu would make possilile the direct calibralion ol the other. Though no such ideal instruments are a\ ailable, it is possible to approach ihe same lesiili by |jroper conn ol ol the amplifier gain, or, what is more coinenient,
. Basic methods for the calibration of sonar equipment. AMPLIFIER RECORDER AND EQUALIZING I SYSTEM I SYNCHRONIZED RECORDING PEN EQUALIZING CHART. Figure 80. .Schematic diagram ot electromechanical equalizer. slant sound held o\ci ilic whole lne|iicncy range, or hydroplioncs which had a uiiilorm response for a consiaiu liild at all Iretiuciu ies, or both. Either in- slitimc'iu would make possilile the direct calibralion ol the other. Though no such ideal instruments are a\ ailable, it is possible to approach ihe same lesiili by |jroper conn ol ol the amplifier gain, or, what is more coinenient, by contiol of the attenuation preceding a constant amplilier gain. The method is indicated in Figure 80, Phchophones are a\ailai)le which have been cali- brated i)y rec iprocity or other means. Using such an instrument with a fixed atienuation and amplifier gain, a recording is made as the projector sweeps over the range of frequencies. From the calibration cur\'e of the hydrophone, a cur\e may l)e plotted which will give the strength of the soimd field jiroduced by the projector at each freciitency. If a straight line is drawn ]jarallel to the recorder axis and at some desired sound level, the difference between it and the projec- tor cur\e will be the numi)er of decibels by which the actual field differs from a constant one. If some device connected to the attenuator can be made to follow the curve and thus \ary the outpm le\el so that it will be projjortional to the deviation of the cui\e from a straight line, the oiit|)tit ol the amplifier will be at a constant level. In other xvords, the record would be that of a flat hydrophone in a constant sound field. If now the coupling loss of an unknown hvdrophone is determined and the corrections for this loss added to the original curve, the resulting control cin-\e will cause the attenuator to correct for both the \ariations in the projector output and the coupling loss. If this hydiophone is placed in the field of the projector
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