User`s guide

Chapter 3 - Receiver Descriptions

Automatic Site Survey (M12+ Timing Receiver Only)

The Automatic Site Survey mode simplifies system installation for static timing applications. This

automatic position determination algorithm is user initiated and can be deactivated at any time.

The Automatic Site Survey averages a total of 10,000 (slightly over 2 1/2 hours) valid 2D and 3D

position fixes. If the averaging process is interrupted, the averaging resumes where it left off

when tracking resumes. During averaging, bit 4 of the receiver status words in the

Position/Status/Data Messages (@@Ha and @@Hb) is set. Once the position is surveyed, the

M12+ timing receiver automatically enters the Position-Hold Mode. At this point, the auto survey

flag is cleared and the normal position-hold flag is set in the receiver status byte of the @@Ha

and @@Hb messages.

Once the antenna site has been surveyed in this manner, the user can expect a 2D position error

of less than 10 meters with 95% confidence, and a 3D error of less than 20 meters with 95%

confidence.

Throughout the survey time the T-RAIM algorithm (if enabled) is active and is capable of

detecting satellite anomalies, however isolation and removal of the bad measurement is not

possible. Once the survey is completed, the T-RAIM algorithm is capable of error detection,

isolation, and removal.

Status of the Automatic Site Survey and Position-Hold Modes is retained in RAM when the

receiver is powered down if battery backup power is provided.

100PPS Output (M12+ Timing Receiver Only)

With the M12+ timing firmware, the timing output can be selected between 1PPS and 100PPS.

This is done using the Pulse Mode command (@@AP). See chapter 5 for information on the

formatting of this command. When selected, the 100PPS signal is output on the same pin as the

1PPS, and has the same accuracy and stability characteristics as the 1PPS signal. Each pulse is

approximately 2-3 ms in duration except for every hundredth pulse, which is 6-7 ms in duration to

allow logic implemented by the user to determine when the top of the second is about to occur.

The leading edge of the pulse following the long pulse corresponds to the top of the second

(referenced to UTC or GPS, depending on the Time Mode selected by the user using the @@Aw

command). Figure 3.6 shows a diagram of the 100PPS output signal.

Motorola GPS Products - M12+ User's Guide Revision 6.X 09FEB05