A LOW FREQUENCY SPECTRUM AND AMPLITUDE DISTRIBUTION ANALYZER
JOHNS HOPKINS UNIV LAUREL MD APPLIED PHYSICS LAB
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In the analysis of time varying signals, two of the important characteristics are the frequency spectrum and the amplitude distribution. The need for equipment to plot these curves automatically from data recorded in the field led to the development of the equipment described in this report. Most of the data to be analyzed were recorded on magnetic tape so that it might be preserved for analysis at a later date. The frequencies of interest in these data were in the region below a few cycles per second. The magnetic tape techniques are well suited for this job because of the frequency multiplication possible by speeding up the playback of the tape. The equipment, as it is now used, operates over the frequency range of about 0.04 to 5 cycles per second. The data recorded on the tape must of sufficient length to give the required accuracy. A given data sample is formed into a closed loop of tape in order to give a repeating function for analysis. The outputs of the system are recorded on a six-channel Brush recorder. Duplicate circuitry is provided so that two signals recorded simultaneously on the same tape can be analyzed both spectra and amplitude distribution at the same time. Thus, there are four outputs on the Brush recorder two spectra and two amplitude distribution curves.
- Test Facilities, Equipment and Methods