Sonar Power

Fish finder power output, measured in watts, determines the maximum depth a fish finder can see.

Fish finder marketing materials frequently quote Watts RMS or peak-to-peak specification. In fact it is very difficult to establish precise performance by reading this value alone because a good fish finder equally requires complex signal receiver processing to evaluate returning waveforms.

It is not technically difficult to apply a high-powered pulse to a transducer. The difficulty is in the interpretation of returning signals. Power output is very important, but it must be considered along with overall device performance.

RMS is typically used to describe average output of a sinusoidal waveform like voltage. Many fish finders specify a value of 500 watts RMS (Root mean square power calculated from a voltage value) but it’s not continuous average power, it is average power for a very brief duration only (other wise the transducer would be cooking!).

Peak-to-peak power describes power output of a fish finder calculated using current and peak-to-peak voltage. Peak voltage is the difference between the lowest voltage peak and the highest peak on an AC waveform. It is a more precise specification when reviewing fish finders because it describes raw power value for some period in time.
The following are some examples of power outputs:

A fish finder may only use up 0.5 Watts or 3 Watts depending on the model. A specification of 500 Watts RMS or 1000 Watts RMS is not meant as continuous power. For example, by taking RMS input power value, e.g. 1 watt and RMS output power, e.g. 100 watts we can estimate that output power is used only 1 percent of the time.

As a thought exercise, if we estimate that power output is turned on for only 1 percent of the time, then a fish finder at 50 KHZ might emit only 500 pulse cycles during a second, while spending the remainder of its processing time receiving and evaluating returned signals.