Measuring the noise in passive mode
Low noise is a key factor for high quality and reliable measurements. The performance of the SU90 system will always be limited by different noise sources. A high noise level will mask the echoes and make them difficult to read and interpret. The noise is measured while the SU90 system operates in Passive mode with the transmit pulses disabled.
Prerequisites
Neither tools nor instruments are required.
Context
This task allows you to check the noise conditions.
Note
Without external noise sources the level should not exceed ≤46 dB. If this level is exceeded in any direction you must locate the noise source(s). If the noise originates on your own vessel we strongly suggest that relevant actions are taken to reduce the noise and thus increase the performance of the SU90 system.
Procedure
1 Select the default settings.
a On the Main menu, select User Settings.
b Observe the Factory Settings list.
c Select the setting you want to use.
d Select Activate Selected Setting.
e Select OK to apply your changes and close the User Settings dialog box.
2 At the bottom of the display presentation, select a suitable presentation mode, and activate the Horizontal view.
3 Make the following preparations.
a On the Main menu: Set Range to 1500 m.
b On the Operation menu: Set Tx Power to Off.
c On the Active menu:
1 Set Pulse Type to CW Medium.
2 Set Frequency to 20 kHz.
3 Set Vertical TX Sector to Narrow.
4 Set Noise Filter to Off.
5 Set the Bottom Filter Threshold to Off.
d On the Setup menu: Open the BITE (Built-In Test Equipment) dialog box.
4 Select Noise to open the page.
5 Finish the test.
a Close the BITE (Built In Test Equipment) dialog box.
b Hoist the transducer back up to its upper position.
Result
For each transmit frequency (in kHz), write down the measured noise levels (in dB).
Frequency Maximum Average
20 kHz  

 
26 kHz  

 
30 kHz