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Acutime 2000 Synchronization Kit User Guide 5-3
5 System Operation
SNR Mask
Although the Acutime 2000 is capable of tracking signals with SNRs
as low as 2, the default SNR mask is set to 4 to eliminate poor quality
signals from the fix computation. Low SNR values can result from:
• low-elevation satellites
• partially obscured signals (for example, dense foliage)
• multi-reflected signals (multipath)
Multi-reflected signals, also known as multipath, can degrade the
position solution. Multipath is most commonly found in urban
environments with many tall buildings and a preponderance of
mirrored glass. Multi-reflected signals tend to be weak (low SNR
value), since each reflection diminishes the signal. Setting the SNR
mask to 4 or higher minimizes the impact of multi-reflected signals.
PDOP Mask
Position Dilution of Position (PDOP) is a measure of the error caused
by the geometric relationship of the satellites used in the position
solution. Satellite sets that are tightly clustered or aligned in the sky
have a high PDOP and contribute to a lower position accuracy. For
most applications, a PDOP mask of 8 offers a satisfactory trade-off
between accuracy and GPS coverage. With worldwide GPS coverage,
the PDOP mask can be lowered even more for many applications
without sacrificing coverage.
!
Note – PDOP is only applicable during self-survey or whenever the
receiver is performing position fixes.