The Sidekiq X4 PCIe Blade includes a Global Navigation Satellite System (GNSS) add-on card
which is based on a uBlox LEA-M8F GNSS module www.u-blox.com/en/product/lea-m8f-module .
The GPS module is capable of using GNSS (9BeiDou, GLONASS, GPS/QZSS), external 10 MHz
frequency sources, and an internal VCTCXO as its disciplining source.
GNSS, if present, will always be used and if GNSS is lost, then the module has 2 options to fallback
on: 1) an external 10 MHz frequency source (if present), and 2) the internal VCTCXO.
*The GPS module has been set up to always use the 10 MHz source as the disciplining source if it is
present on (J4) Ext. 10MHz Input. *
GNSS, if present, will be used if the external 10 MHz is not present. If GNSS is lost, then the M8F
will fallback to using the internal VCTCXO.
Connect the GPS antenna to the GPSDO module’s (J1) GPS Input U.FL connector if you wish to
use the GNSS or connect a 10 MHz reference to the as the disciplining source.
Note: Once a GPS fix has been acquired, a 1PPS signal is also provided. The 1PPS persists after a
GPS fix has been lost
If you wish to supply an external 10 MHz reference clock and 1PPS signal to the Sidekiq X4 **front-
panel **RF connectors, you will need to:
1. Remove the U.FL/W.FL cable connected from the Sidekiq X4’s Ext. Ref CLK (J300) U.FL and
the GPSDO 40MHz Output (J2) W.FL.
Note: This is due to Sidekiq X4 REF 10 MHz Input (J5) sharing the same pad as **Ext. Ref CLK **
(J300).
1. Connect a 10 MHz reference clock to the Sidekiq X4 front-panel REF input.
2. Connect 1 PPS signal source to Sidekiq X4 front-panel PPS input.
3. Change the X4’s reference clock source from host to external by using the ref_clock test
application:
./ref_clock -c 0 –source=external
The NMEA data stream can be viewed by connecting a USB A-Male to B-Male cable from the host
computer’s USB port to the 5-pin header USB-UART on the GPSDO.
USB Ports (Ubuntu): /dev/ttyUSB0 is the NMEA data stream. Note: different serial & GPS drivers
might name the port differently.
sudo screen /dev/ttyUSB0
GPS DISCIPLINED OSCILLATOR (GPSDO)
