Simrad NSO Operation Manual page 41

Noise Rejection
The Noise Rejection control sets the amount of noise filtering applied by the radar. Target
sensitivity is increased at longer ranges when this control is set to Low or High, but does
cause some loss of target discrimination.
Tip: To get maximum range performance from 4G, transmit on one range only, set Noise
Reject control to High and threshold as low as possible. The default is 30% for less
clutter on the screen. If OFF is selected for NSE, NSO and Zeus, the range performance
is about equal to our 3G radar. In some areas where extreme high interference may
exist, try OFF for best radar image.
Fast Scan
The Fast Scan control sets the rotation speed of the radar scanner. For Broadband 4G™
Radar there are Off/Medium/High (24/36/48 rpm nominal) settings. However, Fast Scan
speed will be limited in certain modes of operation:
40 | Using radar
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In Dual Range mode, speed is limited to 24 rpm
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With Noise Rejection set to Low or High, for ranges 1 nm or greater, speed is
limited to 21 rpm.