Topic 09 - About pulse waves

An electrical signal from the fish finder is applied to the transducer, which sends out an acoustic signal - sound waves - into the water column. The transducer receives the reflected echoes from objects that these sound waves encounter and they are sent as an electrical signal to your fish finder. It is the fish finder's job to process this signal into a picture of the underwater world on your screen.


The transducer constantly alternates between transmitting ultrasonic pulse waves and listening for echoes in the receiving mode at a very high speed. Compared with the time the transducer is actively transmitting ultrasonic pulse waves, the time spent 'listening' for echoes in the receiving mode is much longer.

Pulse wave

The transducer in the fish finder transmits ultrasonic pulse waves made up of high pressure and low pressure pulses. The wavelength of each pulse is defined as the distance between two successive high pressure pulses or two successive low-pressure pulses. For example, when an electrical pulse is applied to a 200kHz transducer the element vibrates at a frequency of 200,000 cycles per second – that is, 200,000 individual sound waves are transmitted from the element each second. Short-wavelength, high frequency transducers produce sharp, crisp images on the fish finder display.


Lower frequency wavelengths “see” deeper in the water column than higher frequency wavelengths, and so a boost in power is not always necessary to detect fish in deeper water. The lower in frequency that you go, the deeper the echo sounder will see for the same amount of power. You can also increase the fish finder’s detection range in all frequencies by using a narrower beam transducer. A narrow beam delivers more energy on-target, resulting in stronger echoes, improved target resolution, and the ability to “see” deeper into the water column.