Vicom Spectracom Technical Note

Technical Note:

Outdoor GPS Antenna Installation Considerations

Many Spectracom timing and synchronization products utilize an embedded GPS receiver as a primary reference. Typical
installations utilize an outdoor active GPS antenna to collect and transmit GPS satellite radio signals to the receiver via an RF cable.
This technical note describes the main considerations for a successful outdoor GPS antenna installation for a timing application:

• Locating the antenna

• Connecting to the antenna

• Using ancillary products

• Evaluating signal attenuation to validate cable length

• Using signals in addition to GPS L1

Locating the GPS Antenna
The GPS antenna must have a direct view of GPS satellites with an unobstructed line of sight to the sky. Rooftops that are clear of

other structures or geographic features overhead, with views to the horizon, generally make good installation locations. Such a clear
view allows the antenna to track the maximum number of satellites throughout the day. Installations with obstructed views may
experience reduced reception quality and may not be able to simultaneously track the maximum number of satellites. An
observation angle of 70° from the vertical axis (20° above the horizon) usually offers good performance. Contact Spectracom if your
antenna location’s view of the sky is restricted for mitigating approaches.

When installing your GPS antenna, select a site at which the antenna will not become buried in drifting or accumulated snow. It
should not be covered by foliage or placed in a position where it could become obstructed in this way. Whenever possible, avoid
placing the GPS antenna in close proximity to broadcast antennas or high power transmitters.

Connecting to the Antenna

A coaxial cable transmits GPS signals from the antenna to timing receiver. It also conducts 5 volts from the receiver to power the
antenna and other elements of the antenna system if necessary. The choice of cable is on the basis of attenuation characteristics,
weathering ability, temperature rating, and UV resistance. Type N female connectors are used on the antenna and any other
element in the antenna cable system, therefore male connectors terminate cables. While Type N female connectors are used on
many receivers, smaller form factor products can require the use of alternative connectors. Therefore a different connector may
need to terminate the cable to the receiver or an adapter can be used. The application of weather proofing sealant or tape is a good
idea for all outdoor connections.

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