KVH Industries eTrac - Manual (Page 8)

The Inmarsat-C system is capable of:
• Transmitting data to and from a mobile unit.
• Broadcasting data to groups of mobile terminals.
• Managing position reporting from fleets of mobile units.
• Requesting data from the mobile units via system polling.
1.1.2 The Global Positioning System (GPS)
The eTrac antenna also contains a built-in GPS receiver, which is used to compute the
position of the eTrac system. GPS, developed and controlled by the U. S. Department
of Defense, uses 24 satellites, each of which orbit the earth every 12 hours. At least
four satellites are always visible from any point on earth at any given time. Each
satellite is equipped with hyper-accurate atomic clocks. The satellites simultaneously
transmit signals towards the surface of the earth. The difference in arrival time of the
signals at the eTrac antenna is used to compute the position of the eTrac system.
1.2 Overview of the eTrac System
The eTrac system has three key components. System specifications have been
provided in Appendix A.
The eTrac Antenna Unit
The eTrac Antenna Unit is a compact system built to operate in the marine or outdoor
environment. The Antenna Unit contains a complete Inmarsat mini-C transceiver
with built-in LNA/HPA electronics, a 12-channel GPS receiver, and an omni-
directional antenna designed to operate on vessels and vehicles. The Antenna Unit’s
housing is sealed and contains no user-serviceable parts.
A Guide to the KVH eTrac Satellite Communications System
1-2 www.kvh.com
The Inmarsat mini-C protocol is primarily a text and data system.
While images or attachments can be sent via the system, the
process is very slow and can become expensive. As a result, KVH
recommends that you limit your eTrac transmissions to text and
data messages. If you do send an image or attachment, the
recipient will need to rename the file with the appropriate file type;
the file name and file type are not transmitted.