Motorola M12 Oncore User's Guide download pdf (Page 19)

Chapter 3 – Receiver Description

Motorola GPS Products - Oncore User’s Guide

RF Jamming

Immunity

(continued)

Figure below compares the selectivity of the R5 model of the UT Oncore with the B8

model of the VP Oncore. An additional 30 dB of rejection (an improvement of 1000:1 in

power) has been achieved at the first image O/S 110 dB). The improvement is 15 dB at

the second image (J/S 87 dB). The jamming immunity of the GPS receiver and antenna

system will be further improved with the additional margin provided by the filtering in

the active antenna. Values are typical at 25 degC and a nominal gps power of –130

dBm.

Figure 3.6: Jammer Frequency (MHz)

Note: Jamming tests performed at 25 degC with a nominal gps signal power

of –130 dBm at the RF input of the UT+

Adaptive Tracking Loops

Motorola has developed an innovative software technique to further improve the

Adaptive Tracking Loops jamming immunity of the UT Oncore receiver. The technique

takes advantage of the fact that for precise timing applications, the receiver is not

moving.

In mobile applications of GPS, the receivers must be able to track satellites under

varying dynamics. Vehicle acceleration causes an apparent frequency shift in the

received signal due to Doppler shift. In order to track signals through acceleration, the

tracking loops are wide enough to accommodate the maximum expected vehicle

acceleration and velocity. When the GPS receiver is stationary, the tracking loops do

not need to be as wide in order to track the satellites.

In the UT Oncore 2.x firmware, the satellite tracking loops are narrowed once the

receiver has acquired the satellites and reached a steady state condition. This

adaptive approach allows the tracking loops to be narrowed for maximum interference

rejection while not unduly compromising the rapid startup and acquisition

characteristics of the UT Oncore.

Revision 5.0 08/30/02

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Motorola M12 Oncore User's Guide Page 19