Simrad SN90, Operator'S Manual

Page: 46 / 188

44
381295/B
Selecting operating frequency for minimum noise
The
Frequency
function is used to control the centre frequency of the acoustic
transmissions (pings). The centre frequency can be changed from 70 to 120 kHz in steps
of 1 kHz. All types of noise matter when you wish to find the best operating frequency.
Context
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 SN90 operation.
Procedure
1 On the
Main
menu, select
User Settings
.
a Select
SN90 Factory Default
.
b Select
Activate Selected Setting
.
c 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
BITE
to open the dialog box.
a Select
Noise
to open the page.
b Select
Start Noise Measurements
.
c On the
Active
menu, change the
Frequency
setting while observing the noise
value.
d 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.
Simrad SN90 Operator Manual