User`s guide

Chapter 3 - Receiver Descriptions
Electromagnetic Considerations
The Oncore receiver PC boards contain a very sensitive RF receiver; therefore you must observe
certain precautions to prevent possible interference from the host system. Because the
electromagnetic environment will vary for each OEM application, it is not possible to define exact
guidelines to assure electromagnetic compatibility. The frequency of GPS is 1.575 GHz.
Frequencies or harmonics close to the GPS frequency may interfere with the operation of the
receiver, desensitizing the performance. Symptoms include lower signal to noise values, longer
TTFFs and the inability to acquire and track signals. In cases where RF interference is suspected,
common remedies are to provide the receiver with additional RF shielding and/or moving the
antenna away from the source of the interference.
RF Shielding
The RF circuitry sections on the M12+ are surrounded with an RF dam to provide some
protection against potential interference from external sources. When a design calls for the M12+
to be near or around RF sources such as radios, switching power supplies, microprocessor
clocks, etc., it is recommended that the M12+ be tested in the target environment to identify
potential interference issues prior to final design. In worst-case situations, the M12+ PCB may
require an additional metal shield to eliminate electromagnetic compatibility (EMC) problems.
Thermal Considerations
The receiver operating temperature range is -40°C to +85°C, and the storage temperature range
is -40°C to +105°C. Before installation, you should perform a thermal analysis of the housing
environment to ensure that temperatures do not exceed +85°C when operating (+105°C stored).
This is particularly important if air circulation in the installation site is poor, other electronics are
installed in the enclosure with the M12+, or the M12+ is enclosed within a shielded container due
to electromagnetic interference (EMI) requirements.
M12+ receivers fitted with onboard lithium backup batteries present a special case. Although the
receiver is rated for operation to +85C, the lithium cell has a recommended upper temperature
limit of +60C. Sustained operation at temperatures above this level may result in reduced backup
time and premature battery failure.
Grounding Considerations
The ground plane of the receiver is connected to the four mounting holes. For best performance,
it is recommended that the mounting standoffs in the application be grounded. The receiver will
still function properly if it is not grounded via the mounting holes, but the shielding may be less
effective.
Motorola GPS Products - M12+ User's Guide Revision 6.X 09FEB05
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