V2.0 – Jan-13
User’s Manual
Page 15 of 41
risks ranging from minor impact on TTFF to fatal corruption of flash memory
code area!
GND
1
2
3
4
5
6
7
8
9
C1
0.
1µ
F
C2
0.
1µ
F
C3
0.
1µ
F
C4
0.
1µ
F
C5
0.
1µ
F
RS232 Level Shifter
RS232 Out
DB9
f
em
ale
3.3V
Vcc
GND
T1O
R1I
R1O
T1I
T2I
R2O
C1+
V+
C1-
C2+
C2-
V-
T2O
R2I
MAX3232
Tx
Rx
GND
1
2
3
4
5
6
7
8
9
C1
0.
1µ
F
C2
0.
1µ
F
C3
0.
1µ
F
C4
0.
1µ
F
C5
0.
1µ
F
RS232 Level Shifter
RS232 Out
DB9
f
em
ale
3.3V
Vcc
GND
T1O
R1I
R1O
T1I
T2I
R2O
C1+
V+
C1-
C2+
C2-
V-
T2O
R2I
MAX3232
Tx
Rx
Figure 6: 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
Ω
. Match as close as possible.
3.2 Antennas
Generally, the quality of the GPS antenna chosen (passive or active) is of paramount
importance for the overall sensitivity of the GPS system. Losses through a bad an-
tenna, long cables or tracks or a bad antenna position can’t be compensated after-
wards!
3.2.1 Passive Antennas
The A2100-A supports passive antennas via an integrated LNA directly.
3.2.2 Active Antennas
The A2100-A also supports active antennas directly, i.e. by offering an antenna
voltage feed pin (VANT – pin 15). 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.
