Navman la000508 User Manual

LA000507G © 2006 Navman New Zealand. All rights reserved. Proprietary information and specifications subject to change without notice.

3.6.1 Differential GPS (DGPS)
DGPS specification improves the Jupiter 20 horizontal position accuracy to <4 m 2 dRMS.

3.6.2 Satellite Based Augmentation Systems (SBAS) including WAAS and EGNOS
SBAS improves horizontal position accuracy by correcting GPS signal errors caused by 

ionospheric disturbances, timing and satellite orbit errors. The Jupiter 20 is capable of 

receiving WAAS and EGNOS differential corrections. Both SBAS and DGPS should improve 

position accuracy. However, other factors can affect accuracy, such as GDOP (Geometric 

Dilution of Precision), multipath, distance from DGPS reference station and latency of 

corrections. Note also that XTrac does not support differential aiding.

The Jupiter 20 GPS receiver supports 3D (three‑dimensional) and 2D (two‑dimensional) modes 

of navigation.

 The receiver defaults to 3D navigation when at least four GPS satellites are being 

tracked. In 3D navigation, the receiver computes latitude, longitude, altitude, and time from 

satellite measurements.

 When less than four GPS satellite signals are available, or when a fixed altitude 

value can be used to produce an acceptable navigation solution, the receiver will enter 2D 

navigation mode using a fixed value of altitude determined by the host. Forced operation in 2D 

mode can be commanded by the host.
In 2D navigation, the navigational accuracy is primarily determined by the relationship of the 

fixed altitude value to the true altitude of the antenna. If the fixed value is correct, the specified 

horizontal accuracies apply. Otherwise, the horizontal accuracies will degrade as a function of 

the error in the fixed altitude.

The standard Jupiter 20 with GSW2 software runs at a CPU clock speed of 12.28 MHz. Using 

XTrac software (Jupiter 20S), the clock speed increases to 24.5 MHz. An SDK (Software 

Development Kit) is available from SiRF to customise the Jupiter 20 firmware. Using the SiRF 

SDK the clock speed can be increased up to 49 MHz.
The processing power used by the navigation software is shown in Table 3‑2.

typical performance

2‑3 MIPS

4‑5 MIPS

peak performance

6‑7 MIPS

8‑9 MIPS

The GPS receiver performance of the Jupiter 20 is shown in Table 3‑3.

acquisition sensitivity

–135 dBm

33 dBHz

–135 dBm

33 dBHz

navigation sensitivity

–141 dBm

28 dBHz

–152 dBm

17 dBHz

tracking sensitivity

–143 dBm

26 dBHz

–154 dBm

15 dBHz