GNSS Antennas

The GNSS antennas should be installed level with respect to each other, with a clear unobstructed view of the sky, away from reflective surfaces and with the shortest cable run to the Certus unit permitted by the application. The antennas should be mounted away from any RF emitters such as radars, high-powered communication links, etc. It is important to have a ground plane (flat conductive surface such as a piece of plate aluminium) under the antenna with a minimum radius of 60mm or as recommended by the antenna supplier. Correct antenna positioning is critical for Certus's dual-antenna heading function.

The primary GNSS antenna position offset should be configured in the Certus unit by using the Alignment page in the web UI or Certus Manager. See Using the Web User Interface or Using Certus Manager. The antenna offset is measured from the physical centre of the Certus unit to the central base (ARP) of the primary GNSS antenna in the body co-ordinate frame (X+ forward, Z+ down).

Note: The Z axis is positive downwards, mounting the antenna above the Certus unit will require a negative Z offset. It is very important to set this antenna offset accurately as Certus corrects for lever arm velocities. An incorrect GNSS antenna offset will lead to performance degradation under turning and angular rotations.

An example installation with the body co-ordinate frame axes marked is shown below in Certus antenna offset isometric view and Certus antenna offset front view. In this installation below with an antenna mounted on the right-hand side of the vehicle roof, further forward from the Certus unit, there would be a positive X antenna offset value, a positive Y antenna offset value and a negative Z offset value.

If you are sourcing your own antennas, note the following antenna guidelines:

• The antenna should be capable of receiving both L1 and L2. Heading performance will be significantly degraded with an L1-only antenna.
• Active antennas should have sufficient LNA gain, which when accounting for cable losses, provides at least 33 dB of gain at the connector of the unit.
• The antenna needs to have an accurate phase centre to be RTK capable. This is also required for the dual antenna heading to function correctly. Low performance (low cost) antennas are typically not able to achieve good heading performance.
• The antenna should support GPS, GLONASS, BeiDou, and Galileo.
• The antenna should be environmentally sealed, including connectors.

Antenna Cables

The antenna cables should be routed away from powerful RF emitters, high current wiring, high temperatures and any rotating or reciprocating machinery. It is very important not to bend the antenna cable tighter than its minimum bend radius, or to allow it to be dented. It is recommended to use wide cable ties, loosely fixed in order to avoid damaging the insulation or shielding. The cables should not be coiled. Advanced Navigation recommends:

• Keeping the antenna cables the same length, and as short as possible.
• Using either RG58 low loss or LMR240 coaxial cable combined with high quality connectors. LMR300 and LMR400 can also be used to minimise loss for very long antenna cables.

Cable Type	Minimum Bend Radius	Signal Loss
RG-58/U Low Loss	20 mm	~0.92 dB/m
LMR240	20 mm	~0.33 dB/m
LMR300	22.2 mm	~0.26 dB/m
LMR400	25.4 mm	~0.17 dB/m

GNSS antenna co-axial cable properties

If you are sourcing your own antenna cables it is important to ensure that the antenna has enough gain to support the signal loss over the cable. Certus requires a minimum of 33 dB of gain at the connector. With the standard 4 metre RG-58A/U antenna cables supplied by Advanced Navigation, the minimum antenna gain required is 36.5 dB.

Antenna Suction Cup Mount

A suction cup mount can be used when antennas need to be mounted at any angle or on a smooth, non-porous surface such as a window or on vehicles with aluminium or fibreglass bodies. A suction cup mount can be attached and removed quickly and can easily be moved from one location to another. See Accessories.