ComNav Vector G2 & G2B Installation & Operation Installation
Document PN 29010078 V2.0 - 18 -
DRAFT #3 – 29 May 2009
GPS Reception Considerations
The following points relating to GPS reception must be considered:
• Mount the G2’s enclosure as high as possible, considering maintenance and
accessibility. Ensure that there is an unobstructed as possible “view” of the sky
available to the unit, to avoid blocking the RF signals from the GPS satellites.
• It is important to locate the G2 as far away as possible from any metallic surfaces
that could reflect the RF signals from the GPS satellites.
⇒ Such surfaces, if they reflect the RF signals at “just the right” angle(s), can cause
a condition known as multi-pathing on the signals – which in turn will randomly
degrade the G2’s heading performance and accuracy.
⇒ In particular, there must not be, within a distance of 2 metres of the G2, any
metallic surfaces which are located above the horizontal plane of the enclosure.
• It is also important to locate the G2 away from any transmitting antennas for any RF
signals (e.g., VHF, SSB, Radar, etc.), by at least a few metres. This is to ensure that
the Vector’s internal electronic circuits do not experience induced RF noise, so that
its performance is not compromised.
⇒ If the case of a Radar system, you must also be sure to mount the G2 outside the
direct path of the radar beam – typically, that is a conical shape which extends
outwards from the Radar emitter, and sweeps over a full 360° horizontal circle.
• The G2’s enclosure should be mounted as close as possible to horizontal (when the
boat is at rest in calm water – e.g., at dockside). This is to ensure that the G2’s
internal Tilt sensor can determine the attitude of the enclosure (& thus the vertical
relationship of the two internal antennae).
⇒ A configuration parameter can be used to compensate for any offset from
horizontal, if necessary (see PBIAS on page 55).
• The Vecto
r G2 computes its position as the geographic location of its internal Primary
GPS antenna; that antenna is in the end of the enclosure opposite the end which has
a recessed arrow on the underside & the long-sight alignment post on the top-side
(see Figure 2 & Figure 11). Thus, you should mount the G2 so that the Primary
antenn
a’s e
nd is at the location on the vessel where you desire the vessel’s “reported
GPS position” to be.
Radiobeacon Reception Considerations
For the Vector G2B, it is also important to choose a mounting location with a total view, all
around & right down to the horizon, which is as unobstructed as possible, to avoid blocking
DGPS Radiobeacon signals from any transmitters within range.
You also will need to consider mounting locations from the perspective of minimizing
Electromagnetic Interference (ambient electrical and radio-frequency noise) in the Terrestrial
DGPS Radiobeacon band, in order to maximize the Beacon receiver’s performance.
• The optimum location for the G2B will be a position where it receives the strongest
average Radiobeacon signal, with the lowest average EMI.
• Ensure that the G2B is located as far as possible from all other equipment that can
emit EMI – in particular: DC motors, alternators, solenoids, radios, power cables,
display units and other electronic devices.
• The G2B calculates the Signal to Noise Ratio (which can be thought of as the
“height” of the signal above the noise floor) of the Beacon signals; the higher the
SNR, the better. If your installation includes a way to control & monitor the G2B, you
can observe the SNR values – see the $GPCRQ & $CRMSS sentences in the
Beacon Receiver Commands section in the GPS Technical Reference. You should
have all equipment & accessories that you intend to use during normal operation
turned on, while doing this.
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