User's Manual Part 1

Principles of Operation
P/N 7010-0713
1-5
– Wide Area Augmentation Systems (WAAS, EGNOS, etc.)
creates and transmit, along with DGPS corrections, data
integrity information (for example, satellite health warnings).
– Current ephemerides and almanacs.
Conclusion
This overview simply outlines the basics of GPS and GLONASS
positioning. For more detailed information, visit the TPS website
(www.topconps.com/gpstutorial/).
Receiver Overview
When power is turned on and the receiver self-test completes, the
receiver’s 20 channels initialize and begin tracking visible GPS
satellites. Each of the receiver’s channels can be used to track C/A-
L1, P-L1, or P-L2 signals. The number of channels available allows
the receiver to track all visible GPS satellites at any time and location.
An internal GPS antenna equipped with a low noise amplifier (LNA)
and the receiver’s radio frequency (RF) device are connected with a
coaxial cable. The wide-band signal received is down-converted,
filtered, digitized, and assigned to different channels. The receiver
processor controls the process of signal tracking.
Once the signal is locked in the channel, it is demodulated and
necessary signal parameters (carrier and code phases) are measured.
Also, broadcast navigation data are retrieved from the navigation
frame.
After the receiver locks on to four or more satellites, it is possible to
solve the so-called “absolute positioning problem” and compute the
receiver’s coordinates (in WGS-84) and the time offset between the
receiver clock and GPS time. All this information is stored in the
receiver’s memory, which can be downloaded later onto a computer
and processed using a post-processing software package. When the
receiver is run in RTK mode, raw data measurements can also be
recorded into the receiver’s internal memory. This allows the operator
to double check real-time results obtained in the field.