User's Manual

HE910 Hardware User Guide
1vv0300925 Rev.9 – 07-02-2012
Reproduction forbidden without Telit Communications S.p.A. written authorization - All Rights Reserved page 43 of 80
6.5 GPS Antenna Requirements (HE910 and HE910-GA)
The HE910 module is already provided with an internal LNA amplifier so it is also possible to
develop an application including a passive Antenna.
The use of an active antenna is required to achieve a better performance especially when
the GPS antenna distance from the module is quite high.
The module is provided of a Digital Output signal to enable the external LNA (pad R7)
6.5.1 Combined GPS Antenna
The use of combined GPS antennas is NOT recommended; this solution could generate an
extremely poor GPS reception and also the combination antenna requires additional diplexer
and adds a loss in the RF route.
In addition, the combination of antennas requires an additional diplexer, which adds
significant power losses in the RF path.
6.5.2 Linear and Patch GPS Antenna
Using this type of antenna introduces at least 3 dB of loss if compared to a circularly
polarized (CP) antenna. Having a spherical gain response instead of a hemispherical gain
response could aggravate the multipath behaviour & create poor position accuracy.
6.5.3 LNA and Front End Design Considerations
The optional external LNA (embedded or not inside antenna) should be dimensioned to
compensate antenna line losses and to avoid an excessive LNA gain that can introduce
jamming spurs, degrade 3IP, and saturate the receiver.
The external active antenna for a Telit HE910 device must fulfill the following requirements:
Antenna Requirements
Frequency range
1575.42 MHz (GPS L1)
Bandwidth
± 1.023 MHz
Impedance
50ohm