Installation manual

System description
11
850-164186 / Rev.D
In FM mode each transmission pulse contains up to eight
different frequencies, and the receiver makes a spectrum
analysis and compares the received echoes with the transmitted
frequency code. This provides a filtering effect, which
efficiently reduces interference, noise and reverberation. In
addition to giving a clean and stable echo presentation, this will
normally also increases the sonar’s detection range
Frequency selection (Option)
The optional triple- and multiple frequency selections can be
used for suppression of interference from other sonars.
However, the sound absorption in salt water increases with the
frequency, thus giving the lower frequencies a longer detection
range.
Related topics
 Frequency options, page 6
AGC (Automatic Gain Control)
This control will automatically adjust the gain in the
preamplifiers depending on the strength of the incoming echo
signals. The strength of the filter can be selected in the menu.
Note that the AGC senses the echo strength in five fixed
directions, and use this as a basis for adjusting all the receiver
beams.
RCG (Reverberation Controlled Gain)
The RCG filter senses the noise level (reverberation, propeller
noise, etc.), and adjusts the gain individually for each of the 64
receiver beams in order to eliminate noise on the display. The
strength of the filter can be selected in the menu. With
maximum strenght is selected, the RCG will effectively reduce
the bottom in shallow water, while variations on the bottom will
be displayed.
Note that scattered fish can be perceived as reverberation. The
RCG filter must therefore be used with care if scattered schools
are to be detected.
PP Filter
The SP70 sonar is equipped with a ping-to-ping filter to give a
clean and steady presentation by reducing the interference and
noise. This filter compares the echoes from a selected amount of
transmissions (pings), and an echo has to be present in the
selected amount of pings in order to be presented on the display.