SE868-V3 Product User Guide
1VV0301205 r4 – 2016-01-20
Reproduction forbidden without written authorization from Telit Communications S.p.A. - All Rights Reserved.
Page 21 of 76
Mod. 0805 2015-02 Rev.4
4.10.
Internal LNA
The module has an adjustable gain internal LNA which allows the receiver to compensate for
the use of various external antennas. The default gain (low or high) is determined by the version
of firmware installed in the module. The chart below shows the internal gain modes and the
allowable external gain.
Use the OSP command MID 178,71 to change the gain of the internal LNA.
⋅
Passive antenna:
For passive antenna operations, the internal LNA should be in high gain mode. GPIO8
should normally be left unconnected or connected to monitor the receiver status.
⋅
Active antenna (or External LNA)
:
If an external LNA is used, total RF gain should not exceed the recommend limit of
30dB. When GPIO8 is high, the external LNA should be enabled; when low, it should
be disabled.
Gain Setting
Internal LNA gain
Internal LNA NF
External Gain Range
High
16 dB
2 dB (typical)
0 to 14 dB
Low
6 dB
6.5 dB (typical)
14 to 24 dB
If the external gain is undetermined, use the low gain firmware build
Table 4-1 Internal gain value and external gain range
4.11.
5 Hz Navigation
When this feature is enabled, the receiver starts in 1 Hz mode and continues until it achieves an
over-determined fix with 5 or more satellites. It then computes and outputs solutions 5 times
per second. Each computation uses fewer, but more frequent satellite observations. In most
situations this gives a better response to vehicle velocity and course changes but might cause
slightly more erratic performance in stationary or low-dynamic situations.
The receiver also attempts to send out 5 times as many messages per second. The data rate may
need to be increased or the set of scheduled messages be reduced to avoid overloading the
available bandwidth.
For NMEA protocol, with default messages set on (GGA, GSA and RMC output once per cycle
and GSV output once every 5 cycles) output is nearly 1300 characters per second. Including
start and stop bits, at least 19200 bps is required to avoid running out of bandwidth.
For multi-constellation output, one GNGNS and one GNGSA would be added to each report
cycle, and three GNGSV sentences every 5
th
cycle, requiring a minimum of 38,400 bps data
rate. For OSP protocol, CSR recommends a minimum data rate of 115200 bps.
To enable 5 Hz Navigation, use a $PSRF103 command or an OSP MID 136 command with bit
2 of the pos_mode_enable field set to 1.
