Where should I place my GNSS Antenna?
Single Antenna Systems
Placement of the GPS antenna is crucial to the quality of the data recorded. Any metal close to a GPS antenna can disturb the signal in an unpredictable way due to interference from reflections of weak GPS signals.
For the best results, use the GNSS antenna in the centre of a metal roof or on a metal ground plane of at least 5 cm radius. Make sure that the GNSS antenna is placed away from anything than can cause blockages or multi-path, such as roof bars or radio antennas. Do not mount the antenna close to the edge of the roof as reflections from the ground may interfere with the signals. Avoid the edges as reflections from the pillars and other metal structures will cause problems.
Mount the antenna as high up as possible and keep above any roll bars. Pieces of metal close to and above an antenna will badly disrupt the GPS signal.
Note for non-magnetic surfaces: You can use fabric tape to secure the antenna, as long as it is not metallic. Non-metallic tapes placed over the top of the antenna will not cause any issues at all. We would recommend that any adhesive tape is placed over the top of the antenna and not underneath, to ensure a good contact with the flat aluminium surface.
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If the vehicle being used does not have a metal roof, You can either:
- Place the GPS antenna on a flat piece of metal at least 10 cm in diameter. If this is not possible, you can use copper or aluminium foil to create a shaped ground plane underneath the antenna. For example, on a fibreglass roof, mount the antenna on top of the roof, and place some adhesive-backed metal foil underneath, on the inside of the roof.
- Use a Suction Roof Mount with Steel Plate (RLACS334).
If an antenna is not mounted on a large enough ground plane then the multipath reflections will also be from the ground beneath the antenna. If you are using the antenna on something without a large ground plane (such as a bike or carrying the unit by hand), then you can put a sheet of metal underneath the antenna (can be silver/copper foil), or use an antenna with strong multipath rejection properties (available from Racelogic). These kinds of antennas are much larger and more expensive than the standard antenna supplied with the VBOX, but they can be mounted on a pole to get them as high as possible.
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The GPS antenna should also be placed as far away as possible from any other potential obstructions, such as roof bars or other GPS or Radio antennas. This will reduce the probability of multipath effects.
On a motorbike the antenna should be placed as far from the rider as possible to reduce the satellite signal shadowing effect of the rider. Usually the best place is at the back of the bike, or on the rider’s head. For best results use one of our special GPS antennas which can be mounted on a pole.
Dual Antenna Systems
When testing using dual antenna mode, the greater the antenna separation, the greater the accuracy of the dual antenna-derived data channels.
| Slip Angle Accuracy | Pitch/Roll Angle Accuracy | ||
|---|---|---|---|
| <0.2° rms at 0.5 m antenna separation <0.1° rms at 1.0 m antenna separation <0.067° rms at 1.5 m antenna separation <0.05° rms at 2.0 m antenna separation <0.04° rms at 2.5 m antenna separation |
<0.14° rms at 0.5 m antenna separation <0.07° rms at 1.0 m antenna separation <0.047° rms at 1.5 m antenna separation <0.035° rms at 2.0 m antenna separation <0.028° rms at 2.5 m antenna separation |
Some vehicle roofs limit the potential separation value. In this case a roof mount (RLACS171) can be utilised to increase separation.
Antennas should be positioned so that the gold antenna connector of primary and secondary antennas (A+B) are pointing in the same direction. This matching positioning ensures that the separation measurement is relative.
We recommend you measure separation from outer edge of antenna connector A, to same outer edge of antenna connector B.
Note: Accurate entry of antenna separation is essential for dual antenna operation.
- In pitch alignment, the primary antenna (ANT A) should be placed towards the rear of the vehicle, and the reference antenna (ANT B) placed at the front.
- When in roll alignment, the primary antenna (ANT A) should be placed to the left of the vehicle, and the reference antenna (ANT B) placed to the right.
When mounting the antennas directly to the vehicle roof, ensure that the antenna placement still follows the guidance of the single antenna above (i.e. clear ground-plane, away from obstruction).
Where possible, antennas should be placed on a level plane. The measured distance between the antennas should be the 2D distance between the antennas as viewed from above. It is not the straight-line distance between the antennas, regardless of the mounting angle.
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IMPORTANT Both antenna cables must be the same length! Timing is a very important aspect of the dual antenna lock and identical cable lengths will ensure that signal propagation delays do not cause unreliable dual lock. |
Satellite Elevation Mask
This feature can be used to improve GNSS signal quality when nearby obstacles like trees and building are reflecting or temporarily obscuring the signal from satellites at low elevation. Raising the mask will cause the GNSS engine to ignore satellites below the mask angle, so must be used carefully as it also reduces the total number of received satellites.
The elevation mask angle can be changed in VBOX Setup and by using VBOX Manager.
