. Basic methods for the calibration of sonar equipment. 136 USRL TEST STATIONS and a tentative design is pai'tially completed. The curve tracer mechanism is based on a light-beam and photoelectric cell nidl-l)alancing scheme. Transient \Vave Analyzer In the study of wave iorms, tlie use of the Henrici anal)zer for the measurement and anahsis of tran- sients has proved both time-consinning and expen- sixe. Therefore, USRL later developed an instrument which not only may be constructed from inexpensive and easily available parts Init also speeds up the proc- ess of analysis. (See Figure 81.) Thi
. Basic methods for the calibration of sonar equipment. 136 USRL TEST STATIONS and a tentative design is pai'tially completed. The curve tracer mechanism is based on a light-beam and photoelectric cell nidl-l)alancing scheme. Transient \Vave Analyzer In the study of wave iorms, tlie use of the Henrici anal)zer for the measurement and anahsis of tran- sients has proved both time-consinning and expen- sixe. Therefore, USRL later developed an instrument which not only may be constructed from inexpensive and easily available parts Init also speeds up the proc- ess of analysis. (See Figure 81.) This transparent cylinder is rotated by a motor at about 1,800 rpm running between a light source on the inside and a narrow slit outside. The light passing through the slit impinges on a photoelectric cell of the vacuum photomultiplier type. The associated tidae circuit for amplification is shown at the right of the figure and the power supply at the left. The usual recording sys- tem for any steady-state signal such as system 2 is used beyond this point. In operation, an oscillogram of the transient is re- produced as an opatjue stencil and attached to the surface of the cylinder. It is then rotated between the light source and the photoelectric cell producing an electric signal corresponding to the transient which is repeated some thirty times each second. The en- . velope of the amiilitudes of the Fourier components of this signal is proportional to tiie spectral distribu- tion of energy in the transient. This cn\elope may be obtained directly as a function of the frequency by using system 2 with the 300-c band which will average several adjacent harmonics. The record obtained will be independent of the low-est Fourier frecjuency as long as it is small compared to 300 c. since changing the frequency and amplitude of the linear sweep cor- responds to changing the scale factor in a Henrici analysis. (See references 58 and 79.) Calculations made from this record are identical wit
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