Common issues with using NTRIP for differential corrections

When using NTRIP to receive differential corrections, there are a number of common issues that may arise. This article provides some possible causes for problems receiving NTRIP corrections, although it is by no means an exhaustive list.

Note: this article does not cover troubleshooting the Internal NTRIP Client feature.

Configuration

Configuration issues are a common cause for problems with receiving NTRIP corrections. You should check your configuration to ensure all settings are correct.

There are two major aspects to configuring for NTRIP corrections: the configuration of the INS and the configuration of the interface device connected to the unit to provide corrections (e.g. a Bluetooth RS232 Serial Adaptor or NTRIP modem).

For the majority of our products, configuring the unit to use NTRIP corrections is a matter of configuring the relevant settings in the GNSS Differential Corrections tab in NAVconfig. You will need to ensure that:

1. The Enable NTRIP checkbox is ticked
2. The correction format is the same as that used by the NTRIP provider
3. The serial port settings match those of your interface device

If you are using an xNAV250 or xNAV550, the steps for configuration are slightly different. Instead of configuring these settings in the GNSS Differential Corrections tab, they must now be configured in the Serial Input and Serial 1 Output tabs (under Interfaces).

First of all, in the Serial Input tab, the Input Type must be set to GNSS Differential Corrections. As above, the correction format should be set to that used by your NTRIP provider, and the serial port settings should match those of your interface device.

Note: for these types of units, the Enable NTRIP box will remain grey and cannot be ticked. This is expected behaviour and is not a cause for concern.

Then, in the Serial 1 Output tab, you should configure the Packet as NMEA, and set the GPGGA message to a periodic output of 1Hz. The Baud rate should be set to the same value as in the Serial Input tab.

When configuring your interface device, you should ensure that the settings match what you have set in the INS configuration. Other settings may be dependent on the type of interface device you are using.

Hardware Setup

The hardware being used and the connections between different pieces of equipment in your setup can make a difference to whether or not using NTRIP corrections will be successful.

One of the most common errors in setup is to connect the interface device to the J2 connector on the user cable. It should instead be connected to the J3 connector via a 15-to-9-way serial adapter cable.

Two-way communications are required, as the unit must provide the GGA message to the NTRIP provider; you must therefore make sure the serial adapter cable you are using has both Tx and Rx connected correctly. The pin assignments are shown in the diagram below.

Network and NTRIP Software

If you have checked the configuration and hardware setup, but are still having issues receiving NTRIP corrections, it may be caused by network or signal issues, or problems in the NTRIP client software you are using.

It is worth checking:

• Have you correctly paired your Bluetooth RS232 serial adapter with your smartphone/laptop?
• Do you have a strong enough network signal? You may be able to view the corrections in your NTRIP client software as they are received; you can use this to check whether the problem is with the network or just the connection between your device and your OxTS unit
• Have you selected the correct stream in the NTRIP client software?
• Do you have a valid subscription for the NTRIP service you are using? Are you using a free service?
• Is the phone network you are using blocking the port used by the NTRIP client software?