Simrad SH40
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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 remove 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.
Default setting on the SH40 sonar is Medium .
Pulse form and length
On the SH40 sonar, you can transmit sound modulated as FM or 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.
Default setting on the SH40 sonar is FM Auto . In this transmission mode, the sonar will automatically choose from a set of different frequencies depending on the current range.
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.
Gain
You can adjust the gain in many different ways, but the most important is the setting made by the Gain on the Horizontal and
Vertical menus.
If you have too much gain, you will see a sonar picture with too many echoes. This is because the large amplification presents all kind of noise and reverberation that the sonar picks up. If the gain is smaller the noise and reverberation will disappear, but if it is too small the fish echoes may disappear as well. In most cases you should try with a medium value. On the SH40 sonar, the default value is set to 30.
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