Specifications

WM_PRJ_Q2501_PTS_002 - 001
March 2004
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3.5.3.3 Passive Antenna implementation
It is not advised to use a passive antenna because:
If there is some cable length between the GPS ceramic patch and the
Q2501 module, those losses will not be hidden (no LNA), so the GPS
signal will be lowered, resulting in poor performances.
Even if there is few cable length (< 5 cm), the Noise Factor at the GPS
input connector is the 3 dB Range. The connection between the Q2501
module and the passive antenna could easily add 1 dB (taking into
account losses in the cable and the connectors, mismatch losses).
Consequently the total NF would be degraded to 4 dB Range. Compared
to active antennas, which have typically 1.1 dB NF, there is a 3 dB
losses, that will degrade GPS performances.
The Q2501 module, even shielded, will radiate wideband spectrum
(mostly through the system connector). Even if it complies with EMC
regulations, this noise may degrade the GPS performances.
3.5.3.4 Active Antenna design
Because active antennas are now quite available “on the shelf”, there is no
great interest to build its own active antenna.
Nevertheless, if one wants to design an integrated application (like PDA,
localization tools) that embeds the Q2501 module and a GPS antenna, the
schematic given in Figure 35 is proposed.
Figure 35: Example of Q2501 module and GPS antenna integrated application