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System diagram

The Simrad ST90 fishery sonar is an advanced instrument for efficient fish-finding.

The ST90 systems units are typically installed on the bridge and in a sonar room. The main communication line between the bridge units and the Transceiver Unit in the sonar room is a high-speed Ethernet cable. The Simrad ST90 Fish-finding sonar comprises the following units:

Simrad ST90 system diagram

(A) Display (The second display is optional.)
(B) Processor Unit (computer)
(C) Operating Panel
(D) Transceiver Unit
(E) Hull Unit (Three different types are available.)
(F) Hoist motor
(G) Motor Control Unit
(H) Transducer


A display is a required part of the Simrad ST90 system. For best readability, you must protect the display from glare and have the correct height and angle. The display is not a standard part of the ST90 delivery. This is a commercial item that you can purchase locally.

Processor Unit

The Processor Unit is the computer that controls the ST90 system.

Operating panel

The operating panel contains all necessary control functions for the normal operation of the ST90 system. The controls are arranged in logical functional groups. This offers you clear and easy operation with fast access to key functionality. All the functionality provided by the ST90 system can be accessed using the trackball on the operating panel and the menu system shown in the display presentation.

Ethernet cable

A high-quality Ethernet cable connects the Processor Unit to the Transceiver Unit.

Transceiver Unit

The Transceiver Unit is provided to transmit acoustic energy through water. After each transmission, the transceiver receives the echoes from the seabed and/or the water column. These echoes are filtered, amplified and finally converted into digital format. This transmission and reception sequence is commonly referred to as a ping.

The Transceiver Unit is normally located in the sonar room. It is mounted on the bulkhead using powerful shock absorbers. The physical distance to the hull unit is limited by the length of the transducer cables.

Hull Unit

The hull unit is used to lower the transducer down below the ship’s hull when the ST90 system shall be used. When the ST90 system is turned off, the transducer is hoisted for protection. The hull unit is a large and crucial part of the sonar system.

The ST90 system can be provided with one of the following hull units:

  • ST92: 1.2 metres lowering depth, maximum vessel speed is 16 knots.
  • ST93: 1.6 metres lowering depth, maximum vessel speed is 16 knots.
  • ST94: 2.1 metres lowering depth, maximum vessel speed is 11 knots.