MAX-8 / MAX-M8 - Hardware Integration Manual
UBX-15030059 - R05
Design
Page 14 of 31
Production Information
Active antenna design powered from external supply
Since the external bias voltage is fed into the most sensitive part of the receiver (i.e. the RF input),
this supply should be free of noise. Usually, low frequency analog noise is less critical than digital noise
of spurious frequencies with harmonics up to the GNSS frequency.
Figure 10: MAX-8C/Q and M8C/Q active antenna design, direct external supply (for exact pin orientation see the
MAX-8 Data
Sheet
[1]
and
MAX-M8 Data Sheet
[2])
☞
The circuit shown in Figure 10 works with all u-blox 8 / M8 modules, also with modules without
VCC_RF
output.
External supply (MAX-M8W)
For the module design with active antenna with external supply, see Figure 13
2.4.3
Antenna design with active antenna using antenna supervisor (MAX-
M8W)
An active antenna supervisor provides the means to check the antenna for open and short circuits
and to shut off the antenna supply if a short circuit is detected. The Antenna Supervisor is configured
using serial port UBX binary protocol message. Once enabled, the active antenna supervisor produces
status messages, reporting in NMEA and/or UBX binary protocol (see section 2.4.4).
The current active antenna status can be determined by polling the UBX-MON-HW monitor
command. If an antenna is connected, the initial state after power-up is “Active Antenna OK.”
The module firmware supports an active antenna supervisor circuit, which is connected to the pin
EXTINT. For an example of an open circuit detection circuit, see Figure 14. High on
EXTINT
means
that an external antenna is not connected.
☞
Antenna open circuit detection (OCD) is not activated by default on the MAX-8/M8 modules. OCD
can be mapped to PIO13 (
EXTINT
). To activate the antenna supervisor use the UBX-CFG-ANT
message. For more information about how to implement and configure OCD, see the
u-blox 8 / u-
blox M8 Receiver Description Including Protocol Specification [3]
☞
For recommended parts for the designs that follow, see the Appendix.
2.4.4
Status reporting
At startup, and on every change of the antenna supervisor configuration, the MAX-8/M8 modules will
output an NMEA
($GPTXT
) or UBX (
INF-NOTICE
) message with the internal status of the antenna
supervisor (disabled, short detection only, enabled).
