Trimble Outdoors AgGPS 332 - Manual (Page 26)

2 Overview
1 6 AgGPS 332 GPS Receiver User Guide
24.7
Receiver input / output
The receiver is able to output RTCM in base station mode. When you
are using an external radio, it can also receive DGPS corrections. NMEA
is output when the receiver is exporting GPS position information to an
external device, such as a yield monitor or to a mapping software
program.
24.8
DGPS accuracy
Submeter accuracy from the AgGPS 332 receiver utilizing differential
correction is best achieved under the conditions described in Table 2.6.
Table 2.6 DGPS accuracy
Condition Optimum
Value Description
To calculate a 3D position (latitude and longitude, altitude, and
time), four or more satellites must be visible.
To calculate a 2D position (latitude and longitude, and time),
three or more satellites must be visible.
The number of visible satellites constantly changes and is
typically in the range 5–9. Ag
to 12 satellites simultaneously.
Note – To see when the maximum number of GPS satellites
are available, use the Quickplan utility and a current
ephemeris (satellite history) file. Both files are available free
from:
www.trimble.com/support_trl.asp?Nav=Collection-3627 .
Maximum PDOP < 4 Position Dilution of Precision (PDOP) is a unitless, computed
measurement of the geometry of satellites above the
receiver’s current location.
Note – In some agricultural applications that do not require
high accuracy, a maximum PDOP of 12 or more can be used.
> 6 Signal-to-Noise ratio (SNR) is a measure of the satellite signal
strength against electrical background noise. A high SNR
gives better accuracy.
Minimum
Elevation > 7.5 Satellite that are low on the horizon typically produce weak
and noisy signals and are more difficult for the receiver to
track. Satellites below the minimum elevation angle are not
tracked.