Simrad SD570, Operator'S Manual

Page: 71 / 128

Operation
23
850--160139 / A
There is a choice between five different modes:
FM-AUTO: Chooses automatically the optimal number of
frequencies (1-8) for selected range.
FM-1: Transmits one-frequency pulses with a total
pulse length of 0.6 ms
FM-2: Transmits two-frequency pulses with a total
pulse length of 2.5 ms
FM-4: Transmits four-frequency pulses with a total
pulse length of 10 ms
FM-8: Transmits eight-frequency pulses with a total
pulse length of 40 ms
The chosen number of frequencies are transmitted in one ping,
and the receiver unit undertakes a spectrum analysis and
compares the received echoes with the transmitter’s frequency
code. This provides a filtering effect which efficiently reduces
noise and reverberation, thereby increasing the sonar’s range.
The table on the previous page shows the maximum FM mode for
all ranges. The maximum FM mode will automatically be selected
when using FM-AUTO.