Navigation and Seamanship

3.1.8.1. Transmitter

             First component of echosounder is transmitter. The function of the transmitter is to produce energy in the form of pulses of electrical oscillations. The pulses  of electrical energy  are generated at a specified  frequency. (Frequencies for fisheries applications might be 38KHz,120KHz or 400KHz). In echosounder, the sound wave  is not sent out continuously  but in short bursts (pulses) with longer quiet periods in between. The duration of the short burst is called the pulse length. The duration of the sound pulse is one thousandth of a second (ie one millisecond or 1 ms). Pulses of electrical energy  will be generated by oscillator of the transducer. Pulse gate will determine the duration of the pulse. Pulses will be amplified several thousand times by power amplifier. The power of the pulse produced by the transmitter is an important feature of any echosounder and it may vary from a few watts (w) up to several kilowatts (kw). Pulse power of most echo sounders lies between less than 100 watts to about 1000 watts. Special echosounders for deep sea more and after purposes may have a pulse power of 10kw or more. In general it is advisable to use a high pulse power and low receiver gain in order to obtain clear and better noise – free recordings.