Selecting the best operating frequency

The Frequency function is used to control the centre frequency of the acoustic transmissions (pings). You can select any operational frequency from 14 to 24 kHz. All types of noise matter when you wish to find the best operating frequency.

A lower frequency gives you a better detection range because the attenuation loss is smaller. A higher frequency gives you better range resolution. A higher frequency also gives you narrower beams and a "sharper" image".

Noise from internal and external sources have an impact on the choice of operating frequency. One specific frequency may perform better than the others on your vessel. To measure the noise level, observe the value presented on the Noise page in the BITE dialog box.

We recommend that you do this test twice. First, do the test with all other hydroacoustic systems (echo sounders, ADCP, sonars) turned off. Second, do the test with normal operating conditions. This allows you to see how the other hydroacoustic systems affect the operation and performance of your ST90 system.

Procedure

  1. On the Main menu, select User Settings.
    1. Select ST90 Factory Defaults.
    2. Select Activate Selected Setting.
    3. Select OK to apply your changes and close the User Settings dialog box.
  2. On the Main menu, set Range to 1000 m.
  3. Open the Operation menu. Set Tx Power to Off.
  4. Open the Active menu. Set Pulse Type to CW Medium.
  5. Open the Setup menu.
  6. Select Diagnostics to open the dialog box.
    1. Select Noise to open the page.
    2. Select Start Noise Measurements.
    3. On the Active menu, change the Frequency setting while observing the noise value.
    4. Note frequencies with high noise levels, and try to avoid using them.
    Tip:

    The factory default settings include operating frequency. If you apply these settings remember to make the appropriate changes afterwards.