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Operating procedures
Controlling the gain and range settings
Adjusting the TVG (Time Variable Gain) setting
When an acoustic pulse is sent through the water, it will gradually lose its energy. The greater the distance between the transducer and the target(s), the greater the loss of energy. TVG (Time Variable Gain) compensates for the loss of acoustic energy due to geometric spreading and absorption.

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
- Getting started
- Choosing operating mode and key transmit parameters
- Controlling the gain and range settings
  - Adjusting the gain (echo sensitivity)
    Some echoes are weak while others are stronger. To compensate for this it is often necessary to adjust the sensitivity of the ST90 system. This adjustment is commonly referred to as gain.
  - Adjusting the TVG (Time Variable Gain) setting
    When an acoustic pulse is sent through the water, it will gradually lose its energy. The greater the distance between the transducer and the target(s), the greater the loss of energy. TVG (Time Variable Gain) compensates for the loss of acoustic energy due to geometric spreading and absorption.
  - Adjusting the sonar range
    Some echoes are close, others are further away. It is often necessary to adjust the radius of the search area. On the ST90 system, this is referred to as range.
  - Expanding the range within the sonar view
    In some situations you may wish to expand the range in the sonar presentations. Use View Range to expand the range shown in the relevant views to any percentage of the original Range setting.
  - Adjusting the intensity of the echo presentations
    The effect of the Gain adjustment is minimized if you apply RCG (Reverberation Controlled Gain) and AGC (Automatic Gain Control). The Display Gain is applied at the end of the filter sequence in the ST90 system. This means that you can use Display Gain if you are not completely satisfied with the results of the automatic gain functionality.
  - Changing the tilt
    In order to detect fish or schools in the water column you may need to change the angle of the sonar beams. The transmitted sonar beams can be tilted electronically.
  - Adjusting the bearing
    The Horizontal view presents the 360 degrees area around your vessel from a bird’s eye view. For the other views you must define the horizontal direction of the beam. Use Bearing to adjust the horizontal angle referenced to the vessel heading. You can also select the bearing line and drag it sideways.
- Using the markers and tracking features
- Improving the recognition of fish and schools using receiver filters
- Recording and replaying echo data
- Recording and exporting processed echo data
- Capturing the display presentation in image and video files
- Setting up presentation modes and views
- Defining the visual information in the sonar views
- Defining settings related to user preferences and individual customizing
- Saving, retrieving and maintaining user settings
- Defining the user-selected features on the Operating Panel
- Exporting sensor data, marker positions and technical information
Maintenance procedures
User interface
Menu system
Functions and dialog boxes
Concept descriptions
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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Adjusting the TVG (Time Variable Gain) setting

When an acoustic pulse is sent through the water, it will gradually lose its energy. The greater the distance between the transducer and the target(s), the greater the loss of energy. TVG (Time Variable Gain) compensates for the loss of acoustic energy due to geometric spreading and absorption.

The TVG (Time Variable Gain) compensation is designed to counteract the natural phenomena of geometric spread and absorption loss. In the ST90 system, the TVG compensation is made using digital signal processing software. The TVG compensation is expressed as a logarithmic curve. Each curve has a different slope creating a different gain compensation. Each curve is identified with the equation X log TVG. The coefficient "X" is an integer. Typical values for "X" are 10 to 40.

Procedure

Click in the view you want to activate.
The setting you choose will only be valid for the active view. The active view is identified with a thicker border.
Open the Active menu.
Locate the TVG button.
Select [+] or [-] to choose the requested setting.