3: Quick Start
GPS/GLONASS Receiver Module A5100-A User Guide
17
Figure 7: RS232 level shifter
Remarks:
•
Place C1 to C5 (here: 0.1µF) close to MAX3232. For capacity values see
datasheet of actual component used.
•
Use 3.3V level shifter (MAX3232 or equivalent).
•
External antenna input impedance is 50
. Match as close as possible.
3.2 Antennas
Generally, the quality of the GPS&GLONASS antenna chosen (passive or active) is
of paramount importance for the overall sensitivity of the GPS&GLONASS system.
Losses through a bad antenna, long cables or tracks or a bad antenna position can’t
be compensated afterwards!
3.2.1 Passive Antennas
The A5100-A supports passive antennas via an integrated LNA directly.
3.2.2 Active Antennas
The A5100-A also supports active antennas directly, i.e. by offering an antenna volt-
age feed pin (VANT
– pin 9). It is recommended to use an active antenna with a
supply voltage of 3 to 5 VDC and a maximum current draw of 50 mA. The antenna
should have a gain
≥ 15dB but the total gain (antenna gain minus cable loss at the
antenna input of the module) should not exceed 30 dB. The noise figure should be
≤
1.5dB.
