Trimble Outdoors AcutimeTM2000 Synchronization Kit, Part Number 45005-00-ENG SNR Mask, Pdop Mask

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.

Acutime 2000 Synchronization Kit User Guide 5-3