Vector Sensor Reference Manual 49
second channel continues searching in the background for superior beacon signals. If no signal is
available, the Vector Sensor will initiate a fresh Global Search, continuing this cycle until it finds a
valid station.
3.3.1.3 ABS Background Beacon Search
During the Background Search, the second beacon channel examines all frequencies at both 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 stronger 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.
The beacon module stores the current primary beacon in memory so that it is available upon
subsequent power-up.
3.3.1.4 Manual Tracking
In manual tune mode, you may select a specific frequency and bit rate for the receiver to tune, or
specify the frequency only, allowing the Vector Sensor to identify the correct MSK bit rate on its
own. This mode of operation is most useful when working in an area where you know the
frequency though not necessarily the MSK bit rate of the closest beacon.
3.3.2 Receiver Performance
The Signal to Noise Ratio (SNR) best describes the Vector Sensor’s internal SBX beacon receiver
performance. The SNR, measured in dB, is the height of the signal above the noise floor. The
higher the SNR, the more successfully the beacon receiver is demodulating the signal. You can
easily monitor the SNR in the Beacon Status menu.
Table 3-1 describes the beacon receiver quality of reception with respect to the SNR reading.
Table 3-1 Beacon Receiver Performance - SNR Reading
SNR Reception Description Approximate Data Throughput
>25 Excellent 100% data throughput
20 to 25 Very Good 100% data throughput
15 to 20 Good Good data throughput up to 100%
10 to 15 Stable Moderate to good data throughput
7 to 10 Intermittent Low data throughput
<7 No Lock No data throughput
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