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.

You can compare this gain setting with the volume control on your car radio. When the gain is increased, the echoes will appear stronger. Weak echoes will be easier to see. However, since you also increase the acoustic noise in the reception, the echo presentations will also show this noise. Too much gain may therefore "distort" the presentation.

Comparing the gain function with the volume control on your car radio is not very accurate. In fact, the gain in the ST90 system is constant. The Gain function is used to adjust the sensitivity. This is done by controlling the minimum level of detection. When you increase the gain level (more positive number), you reduce the minimum level of detection, and thus increase the echo sensitivity.

The echo strength (A) changes with time. The minimum level of detection (B) is adjusted up or down with the Gain function. Increasing the Gain with a more positive number reduces the minimum level, and this increases the sensitivity. Only echoes over the minimum level are shown in the echogram (C).

Do not confuse this Gain setting with the TVG (Time Variable Gain) setting.

Tip:

During normal operating conditions we recommend that you keep the gain between 15 and 30. If you need to adjust the gain "from scratch" disable AGC (Automatic Gain Control) and RCG (Reverberation Controlled Gain) to see the immediate effect of the gain adjustments. While you adjust the gain you may find it useful to have a known target (for example an island) as reference.

Procedure

  1. Click in the view you want to activate.

    The active view is identified with a thicker border. Unless you use the Apply to all function, all changes you make will only be applied to this view.

  2. Use the joystick to make the adjustment.
    Tip:

    Optionally: Turn the relevant rotary switch to make the adjustment.

    The Mk2 Operating Panel is fitted with three rotary switches. The switches are identified with numbers. Each switch can be assigned a function related to range, gain, bearing or tilt. Investigate the functionality provided on the Operating Panel page. This page is located in the Installation dialog box.

  • Optionally:

    1. Observe the Main menu.

      Its default location is on the right side of the display presentation.

    2. Select Gain.
    3. Make the necessary adjustment.

      The following methods can be used to adjust this setting:

      1. Select [+] or [-] to choose the requested setting.
      2. Place the cursor on the button. Press and hold the left mouse button. Move the cursor horizontally over the button. Release the mouse button when requested value is shown.
      3. Select the middle of the button to open it. If you have a keyboard connected to the ST90 system, type the requested value.
    4. Open the button and select Apply to all if you wish to use the chosen setting in all the views in the current presentation mode.