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2 Hardware Configuration
14 MiLLennium GPSCard and Enclosures Guide to Installation & Operation
ANTENNA
The purpose of the antenna is to convert the electromagnetic waves transmitted by the GPS satellites into RF signals. An
active GPS antenna is required; a hardware provision is provided to select an internal or external DC power supply for the
active GPS antenna.
An active antenna is required because its low-noise amplifier (LNA) boosts the power of the incoming signals to
compensate for the line loss between the antenna and MiLLennium. The allowable cable loss for an active antenna
system is 13.0 dB. Excessive signal degradation will occur if this limit is exceeded and the MiLLennium may not be able
to meet its performance specifications.
NovAtel offers a variety of GPSAntenna models. All use low-profile microstrip technology and include band-pass
filtering and an LNA. The GPSAntenna you choose will depend on your particular application and hardware
configuration:
L1-Only Antenna Models
•
501 - for surveying applications providing enhanced multipath rejection
•
511 - compact, light and environmentally sealed against rain, ice and lightning strikes
•
521 - delivers optimal performance for airborne, marine and mobile applications
•
531 - for surveying and other kinematic positioning applications
L1/L2 Antenna Models
•
502 - for use in surveying and other kinematic positioning applications (an optional choke-ring ground plane,
NovAtel part number A032, is also available for use with this model)
•
503 - for use with high-performance position-reference stations (features a built-in choke-ring ground plane to
minimize the effects of multipath interference)
•
512 - for installation on aircraft (features aerodynamic styling)
Each of these models offers exceptional phase-center stability as well as a significant measure of immunity against
multipath interference. Each one has an environmentally sealed radome.
NovAtel also offers high-quality coaxial cable in standard 5, 15 and 30 m lengths. High quality coaxial cable should be
used because a mismatch in impedance, possible with lower quality cable, produces reflections in the cable that increases
signal loss.
While there may be other coaxial cables and antennas on the market that may also serve the purpose, please note that the
performance specifications of the MiLLennium are guaranteed only when it is used with NovAtel-supplied accessories.
ANTENNA CONSIDERATIONS
Selecting and installing an appropriate antenna system are important steps to make before operating your GPS receiver.
The antenna you choose for your GPS system will depend on the specific positioning application.
The choke-ring ground plane on the GPSAntenna Model 503 will further reduce multipath errors while maintaining a
stable phase center (e.g. during geodetic survey-quality positioning). An optional choke-ring (Model A032) is also
available for GPSAntenna Model 502.
The MiLLennium has been designed to operate with any of the NovAtel GPSAntenna models. Though it is possible to
operate with other GPS antennas, no guarantee is made that the MiLLennium will meet its performance specifications if a
non-NovAtel antenna is used.
When installing the antenna system,
• choose an antenna location that has a clear view of the sky to the horizon so that each satellite above the horizon can
be tracked without obstruction
• the location should also be one that minimizes the effect of multipath. For a discussion on multipath, please refer to
the chapter on “Multipath Elimination Technology” in the MiLLennium Command Descriptions Manual