Simrad SP90

System descriptionIn addition to the Omni picture, the vertical slice is especiallyuseful for visualizing the vertical distribution of a school of fish.In that way, it is not necessary to go over the target to see thedistribution on the echo sounder, which often results in a spreadingof the school.When the optional stabilization system is installed in the sonar, thehorizontal and vertical beams will be stabilized electronically forroll and pitch up to approximately ±20 degrees. The stabilizationmay be switched on and off in the menu.ReceptionA great effort has been made to reduce unwanted noise to get aclean and stable echo presentation. To achieve this goal the sonarreceiver has the following filtering possibilities:FM Correlation filterIn addition to the traditional single frequency transmitting method,the SP90 sonar is equipped with an FM correlation mode.In FM mode each transmission pulse contains up to eight differentfrequencies, and the receiver makes a spectrum analysis andcompares the received echoes with the transmitted frequency code.This provides a filtering effect, which efficiently reducesinterference, noise and reverberation. In addition to giving a cleanand stable echo presentation, this will normally also increases thesonar’s detection rangeFrequency selection (Option)The optional triple- and multiple frequency selections can be usedfor suppression of interference from other sonars.However, the sound absorption in salt water increases with thefrequency, thus giving the lower frequencies a longer detectionrange.→For more information about this option and the variousfrequencies available, refer to the description on page 5.AGC (Automatic Gain Control)This control will automatically adjust the gain in the preamplifiersdepending on the strength of the incoming echo signals. Thestrength of the filter can be selected in the menu.Note that the AGC senses the echo strength in five fixed directions,and use this as a basis for adjusting all the receiver beams.850-164511 / B9