Installation guide

LMU Users Guide

V1.0.6 December 10 2009

- 64 - CalAmp Proprietary & Confidential

15° filter is enabled by setting bit 5 of S-Register 139. The 5° filter is enabled by clearing bit

5 of S-Register 139.

To enable the 15° filter you would use:

AT$APP PARAM 1024,19,32,32

To enable the 5° filter you would use:

AT$APP PARAM 1024,19,32,0

In general it is best to use the 5° filter for high dynamic applications (e.g. Automotive and

above) and the 15° filter for low dynamic applications (e.g. pedestrian or stationary)

9.4.4 Using Active or Passive GPS Antennas

There are two types of GPS antennas available, an active antenna, and a passive antenna. An

active antenna contains a LNA (low noise amplifier) which receives power from the GPS

Receiver through the antenna cable. This is meant to allow the GPS Receiver to use weaker

GPS signals to produce its location solution.

A passive GPS antenna is not powered and thus the supply voltage normally produced by

the GPS Receiver must be turned off. If the voltage is left on, it may actually damage your

antenna and reduce the overall performance.

By default the LMU assumes it is using an active GPS antenna.

To enable use of a passive GPS antenna you would set bit 5 of S-Register 139.

AT$APP PARAM 1024,19,32,32

To re-enable the use of an active GPS antenna you would clear bit 5 of S-139.

AT$APP PARAM 1024,19,32,0

9.4.5 Update Rate

The LMU supports 2 GPS update rates, a 1Hz rate or a 4Hz rate. At present, the update rate

only affects how often NMEA data is presented on the serial port when NMEA messaging

is enabled. This value is controlled by bit 7 of S-Register 139. If this bit is set, the LMU uses

a 4Hz update rate. If this bit is cleared it uses a 1Hz update rate.

To enable a 4Hz update rate you would use:

AT$APP PARAM 1024,19,128,128

To enable a 1Hz rate you would use: