Furuno FS-1562-15 - Manual (Page 29)

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9958 Squelch activating frequency
Setting range: 500-2000 Hz; Factory setting 1000 Hz.
9959 Sets squelch opening frequency when 2-tone alarm on 2182 kHz is received.
0: No change (frequency set on 9958)
1: 1300 Hz
Factory setting 1: 1300 Hz (Loudspeaker reproduces an audio with an input at
1300 Hz as the squelch opens at that frequency.)
9999 This is for frequency programming by service technicians. Needs a password to
open.
NOTE:
FURUNO Electric Company will assume no responsibility for the inconvenience
or disturbance to communications due to inadequate or unlawful presetting of this
equipment.