SXBlue II GPS Series Technical Reference Manual
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2.8 Evaluating the SXBlue II GPS Performance
The SXBlue II GPS receiver performance has been evaluated with the objective of determining
best-case performance in a real-world environment. Static testing has shown that the SXBlue II
GPS achieves a performance better than 60cm 95% of the time when using WAAS, EGNOS or
MSAS.
The qualifier of 95% is a statistical probability. Often you may see manufacturers using a
probability of ‘rms’ or standard deviation. Performance measures with these probabilities are
not directly comparable to a 95% measure since they are a lower probability (less than 70%
probability). This means that less often, a product would position within a radius of the
prescribed amount.
The following table summarizes the common horizontal statistical probabilities.
Table 2-1 Horizontal Accuracy Probability Statistics
Accuracy Measure
Probability (%)
Rms (root mean square)
63 to 68
CEP (circular error probability)
50
2drms (twice the distance root mean
square)
95 to 98
R95 (95% radius)
95
It is possible to convert from one statistic to another using the following table. Using the value
where the ‘From’ row meets the ‘To’ column, multiply the accuracy by this conversion value.
Table 2-2 Horizontal Accuracy Statistic Conversions
To
CEP
rms
R95
2drms
CEP
1
1.2
2.1
2.4
rms
0.83
1
1.7
2.0
R95
0.48
0.59
1
1.2
F
ro
m
2drms
0.42
0.5
0.83
1
For example, if Product A after test results in an accuracy of 90 cm 95% (R95) and you want to
compare this to Product B that has a sub-meter horizontal rms specification, select the value
from where the ‘R95’ row and the ‘rms’ column intersect (to convert to rms).
You will see that this conversion value is 0.59. Multiply the 90 cm accuracy by this conversion
factor and the result will be 53 cm rms. If you now compare this to Product B’s specification of
sub-meter rms, you can see the Product A would offer better performance.
To properly evaluate one receiver against another statically, they should be using identical
correction input (from an external source) and also share the same antenna using a power
splitter (equipped with appropriate DC-blocking of the receivers and a bias-T to externally power
