Simrad SX90 - REFERENCE MANUAL REV D Reference Manual page 150

Simrad SX90
Table 1 CW and FM pulse lengths for different ranges (cont'd.)
Range CW
(m)
Short Normal
8000 43
148
CW CW FM1
Long
69 85
(Range in meters, pulse lengths in milliseconds)
About CW (Continuous Wave)
The frequency of the transmitter pulse is here constant, equal to
the selected operational frequency. You can select between three
different pulse lengths; short, normal and long. In addition, the
pulse length will also change automatically in accordance with
the selected range. The table above shows the different pulse
lengths given in milliseconds (ms).
About FM (Frequency Modulation)
In the FM mode, the transmitter pulse is frequency modulated.
This provides a stable echo presentation and greater ability of
detection as noise and reverberation are reduced. The frequency
sweep is transmitted in one ping with a centre frequency equal
to the selected operational frequency. The receiver undertakes
a spectrum analysis to compare the received echoes with the
transmitter's frequency code. This provides a filtering effect,
where only "own echoes" are displayed, and noise and other
echoes are reduced. The table on the previous page shows the
FM pulse lengths for all ranges. You can choose between the
following FM modes:
• : This selection will automatically choose the optimal
FM Auto
pulse length for the selected range.
– Ranges from 150 up to and including 900 meters will use
FM4.
– Ranges from 1200 up to and including 8000 meters will
use FM8.
• : You can select between four different pulse lengths;
FM x
FM1, FM2, FM4 and FM8. The selected operating frequency
is modulated with a continuous frequency sweep. The pulse
length will also change automatically in accordance with the
selected range.
Related topics
• Horizontal menu on page 83
• Vertical menu on page 85
• Vertical 180 menu on page 86
FM2 FM4
53 85 85
FM8 FM
Auto
85 FM8
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