Analyzing Signal-to-Noise Ratio
P/N 7010-0935
3-27
Generally, single-frequency receivers are used for baselines with
lengths that do not exceed 15 kilometers (9.32 miles). For baselines of
15 kilometers or greater, use dual-frequency receivers.
Dual-frequency receivers have two major benefits. First, dual-
frequency receivers can estimate and remove almost all ionospheric
effect from the code and carrier phase measurements, providing much
greater accuracy than single-frequency receivers over long baselines
or during ionospheric storms. Secondly, dual-frequency receivers
need far less observation time to reach the desired accuracy
requirement.
After the survey completes, data the receivers collect can be
downloaded onto a computer and processed using post-processing
software (for example, Topcon Tools).
Analyzing Signal-to-Noise
Ratio
Knowing the strength and reliability of the ranging signal transmitted
from the satellites will help determine the quality of the satellite
signals. Use Table 3-4 to help estimate signal quality from a satellite
vehicle.
If the SNR value of a satellite signal is less than the threshold value
from the table, then pay close attention to this satellite because it can
Table 3-4. Typical SNR Values
SV
a
Elevation
(degrees)
a. SV = satellite vehicle
C/A channel
(dB*Hz)
P1 channel
(dB*Hz)
P2 channel
(dB*Hz)
10–20
>35
>10
>10
20–40
>40
>20
>20
40–60
>45
>30
>30
60–90
>50
>40
>40
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