User`s guide

Chapter 3 - Receiver Descriptions
The M12+ Oncore receiver is capable of tracking twelve satellites simultaneously. The module
receives the L1 GPS signal (1575.42 MHz) from the antenna and operates off the
coarse/acquisition (C/A) code tracking. The code tracking is carrier aided. Time recovery
capability is inherent in the architecture.
The L1 band signals transmitted from GPS satellites are typically collected, filtered, and amplified
by microstrip patch antennas such as the Motorola Hawk or Timing 2000. Signals from the
antenna module are then routed to the RF signal processing section of the M12+ via a single
coaxial interconnecting cable. This interconnecting cable also provides bias power for the low-
noise-amplifier (LNA) in the antenna. The M12+ is capable of providing the antenna with voltages
from 2.5-5.5V at currents up to 80mA.
The RF signal processing section of the M12+ printed circuit board (PCB) contains the required
circuitry for down-converting the GPS signals received from the antenna module. The resulting
intermediate frequency (IF) signal is then passed to the twelve channel code and carrier
correlator section of the M12+ where a single, high speed analog-to-digital (A/D) converter
converts the IF signal to a digital sequence prior to channel separation. This digitized IF signal is
then routed to the digital signal processor where the signal is split into twelve parallel channels for
signal detection, code correlation, carrier tracking, and filtering.
The processed signals are synchronously routed to the position microprocessor (MPU) section.
This section controls the receiver operating modes, decodes and processes satellite data, and
the pseudo-range and delta range measurements used to compute position, velocity, and time. In
addition, the position processor section contains the inverted serial interface.
Memory Backup
Frequently, backup batteries are used with M12+ receivers. Use of a backup battery is not
mandatory, but can be useful for saving setup information and increasing the speed of satellite
acquisition and fix determination when the receiver is powered up after a period of inactivity.
M12+ receivers may be ordered with or without a rechargeable lithium cell onboard, use an
external backup voltage source, or operate without any backup source whatsoever.
Battery equipped M12+ receivers are fitted with 5 mAh cells, sufficient for 2 weeks to a month of
backup time, depending on temperature. Note that these cells ARE rechargeable types, and in
order to charge them the receiver MUST be powered up. A factory fresh receiver should be
allowed to run for 24-36 hours to provide the battery with an initial full charge.
Operating With a Backup Source
If employed, the backup source keeps the RAM and the Real-Time Clock (RTC) in the receiver
alive, saving setup and status information. Time, Date, Last Calculated Position, Almanac, and
Ephemeris information, along with receiver specific parameters and output message configuration
are all saved, making resumption of operation once main power is restored essentially automatic.
In this “Warm Start” scenario the power comes back on, the receiver looks to the RTC to see how
much time has elapsed since power was removed, calculates which satellites should be visible
using the stored almanac information, and then proceeds to develop fix information, outputting
data in the same formats that were active when power was removed.
Motorola GPS Products - M12+ User's Guide Revision 6.X 09FEB05
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