Haicom HI-204E - Manual (Page 17)

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As long as enough satellite signals are received to generate
valid position fixes, the 1PPS output remains synchronized
to the GPS second, and the 1PPS Valid Signal remains
active. If signal blockage prevents the receiver from
generating valid position fix, the 1PPS output will drift away
from the GPS second and the 1PPS Valid Signal will
become inactive. Upon re-acquiring enough satellites to
generate consecutive valid position fixes, the 1PPS Valid
Signal will become active again, signaling that the 1PPS
output is again synchronized with the GPS second.
For best stable operation of the 1PPS signal, it is to be
operated in static environment having clear view of the sky.