SX BLUE GPS iSXblue II+ GNSSTM, Руководство пользователя

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SXblue Series User Manual 77
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 may 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.
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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 2dB 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.
The SXblue II-B GPS stores the current primary beacon in memory so that
it is available upon subsequent power-up. You may force a new GS at any
time using the $PCSI,4 proprietary NMEA 0183 command defined in the
Technical Reference Manual.
3.3.2 Manual Mode
In Full Manual Tune mode, you may specify a frequency and bit rate for the
receiver to tune to or specify the frequency only, allowing the SXblue II-B GPS to
identify the correct MSK bit rate automatically (Partial Manual Tune mode). Setting
manual operation is discussed in the Technical Reference Manual, using the
$GPMSK NMEA 0183 command.
Acquisition of a beacon in manual tune mode is dependent upon the data rate of
the station. In Full Manual Tune mode with an MSK rate of 200 bps, signal
acquisition should occur within 5 seconds if no demodulation errors occur. Signal
acquisition should occur within 10 seconds for a modulation rate of 100 bps
provided that no demodulation errors occur.
Partial Manual Tune mode requires that the SXblue II-B GPS identify the correct
MSK rate automatically. This automatic detection could result in signal acquisition
rates of up to approximately 15 seconds.
3.3.3 Database Mode
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Operating Mode