Garmin TracPak GPS 30/30 SL Manual page 10

1.4.1 Application Considerations
1) Interruptions in GPS RF signals can increase the
Time To First Fix (TTFF). Antenna location with
continuous clear line-of-sight visibility to all directions
in the sky yields the best TTFF.
2) GPS signal reception quality can be determined by
monitoring the signal to noise ratio fields in the
$GPGSV sentence. Typical values will be between
33 to 51 dbHz. Values below 43 dbHz for the highest
elevation satellites may indicate a need to re-locate
the antenna if marginal performance is noted (long
TTFF).
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