u-blox LEA-M8S, Hardware Integration Manual

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LEA-M8S / LEA-M8T - Hardware Integration Manual
UBX-13003140 - R07 Production Information Design
Page 15 of 31
Message Description
ANTSTATUS=DONTKNOW
Active antenna supervisor is not configured and deactivated.
ANTSTATUS=OK
Active antenna connected and powered
ANTSTATUS=SHORT
Antenna short
ANTSTATUS=OPEN Antenna not connected or antenna defective
Table 4: Active antenna supervisor message on startup (NMEA protocol)
Module design with active antenna, short circuit protection / detection
If a suitably dimensioned R_BIAS series resistor is placed in front of the V_ANT pin, a short circuit can be
detected in the antenna supply. The detection happens inside the u-blox M8 module, after which the antenna
supply voltage will be immediately shut down. Afterwards, periodic attempts to re-establish antenna power are
made by default.
An internal switch (under control of the receiver) can turn off the supply to the external antenna whenever it is
not needed. This feature helps to reduce power consumption in power save mode.
To configure the antenna supervisor use the UBX-CFG-ANT message. For further information, see the
u-blox M8 Receiver Description Including Protocol Specification [3].
Short circuits on the antenna input without limitation (R_BIAS) of the current can result in
permanent damage to the receiver! Therefore, it is mandatory to implement an R_BIAS in all
risk applications, such as situations where the antenna can be disconnected by the end-user or
that have long antenna cables.
In case VCC_RF voltage does not match with the antenna supply voltage, use a filtered external supply
as shown in Figure 13.
Supply from VCC_RF
Figure 12 shows an active antenna supplied from the LEA-M8S and LEA-M8T modules.
LEA-M8S and LEA-M8T modules includes a built in antenna bias supply for nominal 3V antennas enabled by
linking the filtered
VCC_RF supply output pin to the V_ANT antenna supply input pin with a 10 Ohm resistor in
series. The module then controls the power supply to the antenna, applying power whenever the receiver is
active and removing power during power-save idle times and if a short-circuit is detected. Short-circuit is
detected if the voltage at the antenna supply falls close to zero and is indicated as an alarm in message MON-
HW
Figure 12: Module design with active antenna, internal supply from VCC_RF (for exact pin orientation see the LEA-M8S Data
Sheet [1] and the NEO/LEA-M8T Data Sheet [2].)
For recommended parts, see Appendix.