Minelab F3 Mine Detector Operation Manual page 36

 Noise Cancel will commence with two single beeps followed by
45 seconds of sharp double beeps finishing with four single
beeps.
 During the 45 seconds, the detector scans the environment
searching for any electrical interference. Once detected, the F3
will automatically select a different operating frequency to
eliminate or reduce the interference.
b. Audio Reset. Whenever the Threshold Tone sounds louder than
normal perform the Audio Reset procedure as follows:
The detector cannot be used for clearing operations during the
Audio Reset procedure.
 Audio Reset should be carried out whenever the threshold
volume seems louder than normal.
 Hold the coil away from any metallic objects.
immediately release the Ground Balance button (Green Button
Figure 21: Noise cancel
NOTE
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Press and