CSI Wireless SBX-3, Справочное руководство

Страница: 57 / 110

SBX-3 Reference Manual
39
This initial phase of the GS takes approximately 3 to
4 seconds to scan all 84 beacon channels in the frequency band using
both channels. Once scanned and with SS numbers identified for each
beacon channel, both receiver channels cooperatively examine the
frequencies with the highest SS measurements, above the computed
noise floor, to determine the station providing the strongest RTCM
signal. The receiver's primary channel locks to the first identified
DGPS broadcast, while the second channel continues searching in the
background for superior beacon signals. If no signal is available, the
SBX-3 will initiate a fresh Global Search, continuing this cycle until it
finds a valid beacon.
The secondary acquisition phase of the GS composes the remainder of
the time required to acquire the beacon signal. The time required to
acquire a beacon in ABS mode is dependent upon the signal quality of
DGPS beacons in your area, and their relative strength to other non-
DGPS beacon signals in the 283.5 to 325.0 kHz band. As this
frequency range is a navigation band, it is shared with other navigation
aides such as non-directional beacons used for aviation and marine
navigation. Depending on the signals available, initial acquisition make
take less than 15 seconds for a strong beacon station, from a cold
start, or up to a couple minutes if a beacon site is weak relative to other
signals. During the acquisition phase, if bit errors occur due to a weak
DGPS beacon signal or environmental noise occurs, the time to
acquire may be longer.
3.6.1.2 ABS Background Search
During the Background Search, the second channel examines all
frequencies at both the 100 and 200 bps MSK bit rates to identify
beacons possessing superior signal quality. If a DGPS broadcast is
identified that exhibits a 2 dB greater signal strength than that of the
primary station, the receiver will automatically switch to this beacon.
No loss of lock occurs on the primary station during the background
scan process. If the secondary receiver channel finds a superior
station, the main channel is instructed to tune to the new beacon.