Page 8
DXD/PTP/GPS User Manual (rev 2.10)
6. GPS Menus
6.1 SATELLITES SELECTION (MENU 6.1)
The DXD/GPS receiver is a multi-GNSS (Global Navigation Satellite System) timing receiver able to receive concurrently the
signals of multiple navigation satellite systems. GPS was the first GNSS system deployed but today, other satellite navigation
systems are in operation such as GLONASS of Russia, Galileo of Europe, BeiDou (Compass) of China. Moreover, SBAS
(Satellite Based Augmentation System) a network of the geostationary satellite systems (WAAS of United States, EGNOS of
Europe, MSAS of Japan) is in operation and Japan has started the operation of QZSS (Quasi-Zenith Satellite System).
Menu 6.1 lets you select which satellite constellations the DXD/GPS will be connecting to from the following selection:
•GLONASS
•Galileo
•QZSS L1C/A
•SBAS/QZSS L1S
Note that the
GPS
constellation is always enabled.
If your antenna is multi-GNSS, enabling multiple satellites constellations in this menu will increase the total number of available satellites.
In environments with limited open space, access to more visible satellites will translate into greater synchronization accuracy.
6.2 GPS SETTINGS (MENU 6.2)
•Antenna Cable Delay
This field in menu 6.2 allows you to compensate for cable delay and other latencies with a range of ± 100 µsec with a 1
nsec resolution. The default value is 0.
When designing an antenna system, cable length must be taken into consideration, as it can not only impact the signal
strength but also cause a delay in the signal. Under typical conditions however, the expected cable delay is negligible,
in the nanoseconds range.
The following formula is used to calculate the cable delay: Tc = L/cv, where L is the cable length in meters; c is the speed
of light (3.0 x 10
8
m/s); and v is the velocity factor of the cable expressed as a number less than 1.
The correct value of v can be found in the cable manufacture’s specifications.
•Antenna High Gain
This field gives the option to turn up the LNA gain (Low Noise Amplifier).
Most installations will use a high-gain active antenna therefore the default value is OFF. However, if using a passive
antenna or a low-gain active antenna, this should be ON.
•Estimated Accuracy Threshold
A value in ns from 20 to 9999 can be entered. ‘No Threshold Test’ is the default value. This is one of the criteria used by
the DXD to determine if the GPS signal can be used as a reference. The estimated accuracy is indicated on the GPS
Receiver stays page.
6.3 ADVANCED GPS SETTINGS (MENU 6.3)
Menu 6.3 provides additional parameters, referred to as ‘advanced’, as, in most cases, they will not need to be modified and
are only provided for unusual situations requiring additional adjustments.
•Survey Sigma Threshold
Survey Sigma Threshold has a default value of 10. If your DXD/GPS is having difficulties in achieving lock, increase the
Sigma value.
•Survey Time Threshold
Survey Time Threshold is set by default to 24hrs. This survey time restarts each time the DXD is turned on. If you would
like to achieve lock faster, decrease the Time value.
