Can one make relative measurements in a tank using a Spectrum Analyzer?
No. While one might assume that, regardless of distortion, one could compare the relative levels of two transmitters by measuring the total spectral energy, the problem is that even minor differences in positioning can have a significant impact of how echoes and direct signal combine. As a consequence, even the same transmitter positioned as carefully as possible each time can produce markedly different results in successive measurements (see Figure 2). Therefore, measurement of energy in a tank where echo strength is significant is meaningless. Figure 2: Hydrophone output from two consecutive measurements of same transmitter with transmitter repositioned between the two measurements.
