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Concept descriptions
Acoustic noise
Electricalselfnoise
Electrical or electronic self noise is picked up or generated in any other part of the equipment than the transducer.

About this manual
The purpose of this publication is to provide the descriptions, procedures and detailed parameter explanations required to allow for safe and efficient use of the ST90 system. The publication also provides you with a thorough understanding of the parameters and adjustments provided by the ST90 system.
Simrad ST90
Operating procedures
Maintenance procedures
User interface
Menu system
Functions and dialog boxes
Concept descriptions
- Important settings
- Basic sonar theory
- Acoustic noise
  - Introduction to the acoustic noise challenge
    Even with the advanced noise filtering offered by the sonar system, we must address the noise challenge. This is important during the planning and preparations for the system installation. The echoes from any large and small target must be detected inside the noise.
  - Contributing factors
    Several factors are contributing to the performance of the hydroacoustic equipment used on board a vessel.
  - Self noise
    Any vessel equipped with a hydroacoustic system (for example echo sounder or sonar) will produce more or less self noise.
  - Ambientnoise
    Ambient noise is usually not a limiting factor to the performance of sonars and echo sounders.
  - Electricalselfnoise
    Electrical or electronic self noise is picked up or generated in any other part of the equipment than the transducer.
  - Reverberation
    When you transmit an acoustic pulse into the water to search for a target, echoes will also be returned from any other objects in the beam. The energy reflected from these "unwanted" objects is referred to as reverberation.
  - Some means to reduce acoustic noise
    Several factors are contributing to the performance of the hydroacoustic equipment used on board a vessel. Careful planning of the installation may reduce the acoustic noise.
Technical specifications
The technical specifications summarize the main functional and operational characteristics of the ST90 system. They also provide information related to power requirements, physical properties and environmental conditions.
Datagram formats
The ST90 system can send and receive information to and from several different peripherals. All transmissions take place as datagrams with data sentences. Each datagram has a defined format and length.
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Electrical self noise

Electrical or electronic self noise is picked up or generated in any other part of the equipment than the transducer.

The most common source of electrical self-noise is hum. Hum is typically generated by low-quality power supplies. Transducer cables and sensitive electronic circuitry can easily pick up hum. At higher frequencies – where rather wide bandwidths are necessary – the noise from components, transistors or other analogue electronic may be a limiting factor.