Operation Manual

Simrad SH80
120
850-164385 / Rev.C
CW (Continuous Wave)
The frequency of the transmitter pulse is here constant, equal to
the selected frequency (if the optional multiple frequencies are
installed).
There is a selection between three different pulse lengths:
Short, Normal and Long. In addition the pulse length will
change automatically in accordance with the selected range. The
table shows the different pulse lengths given in milliseconds
(ms).
Auto
In Auto mode, the transmitter pulse is made with a combination
of FM and CW to give an optimal echo presentation for all
ranges. This combination is designed from operational
experience, and will change automatically between FM Long in
the shorter ranges, and CW Long in the longer ranges. The
table shows the mode and pulse lengths (ms) which are used for
the different ranges.
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.
There is a selection between these different FM modes:
 FM Short - Transmits one-frequency pulse with a total pulse
length of 3.2 ms for all ranges.
 FM Normal - Transmits one-frequency pulses with a total
pulse length of 6.4 ms up to the ranges of 150 meters, and
two-frequency pulses with a total pulse length of 12.8 ms for
the longer ranges.
 FM Long - Transmits one-frequency pulses with a total pulse
length of 6.4 ms up to the ranges of 300 meters, and
four-frequency pulses with a total pulse length of 25.6 ms for
the longer ranges.
The selected number of frequencies are transmitted in one ping,
and 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 maximum FM mode for all ranges.