The circuits that power the transducer to create the ultrasonic energy pulse can properly be called a transmitter. As with the more familiar radio transmitter, the power rating assigned by the manufacturer can be mislead the technically uninformed. Output power levels are often quoted as peak pulse power, peak-to-peak pulse power, rms power or average power. (Root-mean-square, RMS power is an engineering measurement means for equating the total energy in an alternating current waveform to the average or heating power in a direct current circuit.) Interestingly, some of the very smallest and least costly depth sounders and fish finders may carry power specifications of 2,000 watts while drawing only one quarter of an ampere from the boat's 12 volt power system. This seeming impossibility is explained by the fact that the high power quoted for the unit, 2,000 watts, exists only for a small fraction of the time the unit is operating. In this example, the average input power is only 3 watts. The rms power rating is 200 watts, indicating that pulses are being transmitted only about 1% of the time. The 2000 watt peak-to-peak power rating is accounted for by the extremely short duration of each pulse. The rms power of most recreational depth sounders and fish finders range between 100 and about 600 watts. As with most complex systems, raw power is not necessarily a good measure of overall results. The quality of the transducer, the sensitivity and selectivity of the receiver circuits and the type of data processing used in deriving information from the returning acoustic echo will determine the results achieved with a given sounder or fish finder.
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