Simrad SH90 - REV A, Руководство оператора

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Simrad SH90
What is AGC?
AGC
means Automatic Gain Control . The AGC will
automatically scale the received echo data to maintain a proper
dynamic range based on all the incoming echo values. In addition
to
Off , the strength of the filter can be set to three different levels.
What is the PP Filter?
PP Filter
means Ping-to-Ping filter . When this function is
activated, the sonar will compare the echoes from one ping with
the echoes from the next pings. If an echo is present at the first
ping, but then disappears at the next, the sonar will interpret this
as noise and reverberation, and suppress it.
If you choose setting
Weak
, the sonar will only compare two
consecutive pings. If you choose settings
Medium
or
Strong
the
sonar will compare four and eight pings respectively.
About pulse form and length
On the SH90 sonar, you can transmit sound modulated as
• FM
• CW
FM
means frequency modulated , which means that the frequency
of the transmitted pulse is changed during the transmission. In
most cases this method will provide better echo presentation and
stability, and you will avoid excessive noise and reverberation.
CW
means continuous wave , which means that the transmission
frequency is fixed during the entire pulse. When you use CW
transmission you can choose the length of the pulses. In a search
phase under good conditions, you should try setting
Long
. If the
conditions worsen, try to shorten the pulse length. This will make
it easier to distinguish the various echoes, and the reverberation
will be reduced.
The default setting on the SH90 sonar is
FM Auto
. In this
transmission mode, the sonar will automatically choose the
optimal pulse length for the current range.
About beam widths
A narrow beam will always reach further than a wide beam. This
is because the transmitted power of the sonar is concentrated.
Nevertheless, you can easily “miss” a school of fish if you make
the beam too narrow. If the range is reduced, it is the common to
use a wider beam.
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