# Analysis of Satellite Compass Error's Spectrum
## 2 Materials and Methods
### Devices  
The satellite compasses of three different manufacturers were used in the experiments presented in this paper. These are Novatel PwrPak7D, the Advanced Navigation GNSS compass in a low-cost variant and Furuno SC-50. Basic parameters, based on specifications provided by manufacturers, are presented in Table 1.  
Novatel PwrPak7D-E1 is a robust GNSS receiver that combines dual antenna signal and (INS)--inertial navigation system hardware in a single enclosure to provide easy-to-deploy industry-leading position and heading data. In this experiments, two G5 Ant-4 AT1 models made by Antcom were used. According to the manufacturers, the device is suitable for ground vehicle, marine and air-based systems. Its software takes into account SPAN (synchronous position, attitude and navigation) technology based on GNSS+INS sensors as well as ALIGN software for angular determinations. It uses an OEM7720 receiver card and Epson G320N MEMS (IMU)--inertial measurement unit.  
Advanced Navigation is a compact, low weight device, designed for marine and automotive applications, including small-size vehicles. It contains a 9 axis IMU that is integrated with a dual antenna GNSS receiver. Antennas are placed inside a 672 mm enclosure, together with all the signal processing electronic components. This seems to be around 3.25 lengths of the L1 wave of distance between the centers of the antennas. The core of this device is composed of two u-blox M8T GPS modules. The incorporation of all the processing components into the antennas enclosure makes it easy to integrate it even in restricted space conditions. Data are sent through the serial cable or via the (NMEA) National Marine Electronics Association 2000 network. The device is certified to be used on commercial vessels.  
Furuno SC-50 is a popular satellite compass for commercial shipping. The large size of its processing unit qualifies it specifically for use on vessels. With its three-fold antenna, it can be useful for surveying ships. Clear display is designed for installation on the vessel's bridge, although data or data recorders can be sent to other devices using the standard marine format, NMEA 0183, or NMEA 2000 with the proper converters. The SC-30 antenna unit applied in tests consists of three antennas in  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**No.** & **Feature** & **Novatel PwrPak7D-E1** & **Advanced Navigation** & **Furuno SC-50** \\ \hline
1. & Position accuracy & 0.6 m (DGNSS) & 2.0 m or 0.6 m— (DGNSS) & 3–10 m (depending on corrections) \\ \hline
2. & Velocity accuracy & 0.03 m/s & 0.05 m/s & no data \\ \hline
3. & Roll and pitch accuracy & no data & 0.4\({}^{\circ}\) & no data \\ \hline
4. & Heading accuracy & 0.1\({}^{\circ}\) (for 2 m base length) & 0.2\({}^{\circ}\) (base length 620 mm) & 0.5\({}^{\circ}\) RMS (base length 430.3 mm) \\ \hline
5. & Heave accuracy & no data & 5\% or 0.05 m (whichever is greater) & no data \\ \hline
6. & Output data rate & Up to 100 Hz & Up to 100 Hz & Up to 40 Hz \\ \hline
7. & Base length & adjustable & permanent & permanent \\  & & & 620 mm & 430.4 mm \\ \hline \multirow{3}{*}{8.} & & & GPS L1 & \\  & & GPS & SBAS & \\ \cline{1-1}  & navigation systems & L1, L2 & GALILEO E1 & GPS L1 \\ \cline{1-1}  & & & BeiDou B1 & \\ \hline \hline \end{tabular} Where: (GPS) Global Position System, (SBAS) Satellite Based Augmentation System, L1, L2—frequency of GPS, (RMS) Root Mean Square, DGNSS - Differential Global Navigation Satellite System.  
\end{table}
Table 1: Basic technical parameters of the three compared satellite compasses used in the experiments [19; 20; 21].  
one robust housing with a 650 mm diameter and a distance between the centers of the antennas of 430 mm. This is about 2.25 of the L1 wave length.  
In summary, three different GPS receivers with different antennas and different distances between them, as well as different algorithms for angular calculations, were tested. The data were acquired with a data recording rate of 1 Hz.