There are two methods of using the serial interface:
- Radio modem receiving from a base station (radio link)
- External NTRIP modem receiving from an NTRIP caster (cellular Internet)
This article will also discuss:
- Things to remember
- Troubleshooting radios
- Common issues with using NTRIP for differential corrections using the serial interface
To receive corrections via the serial interface, the radio or NTRIP modem must either be connected to the 9 or 15 pin serial port on the user cable. If the 9-pin port is used, the modem will require an external power source.
Corrections from a base station using a radio modem does not require a feature code and only the correction format needs to be selected. RTCM v3 is the default but can be changed using the drop-down menu shown below.
Important things to remember when using a base station - if you require repeatable data, then the location of the antenna must not move. If the antenna moves, the location of the remote receivers also moves.
Configuring NTRIP is slightly different, the tick box for NTRIP needs to be enabled as seen below. An external NTRIP client is required to connect over serial, e.g. an NTRIP modem.
Correction formats and available units
RTCA: RT3000 units, including RT2000, RT4000 and Survey+
RTCMv3: All units
CMR: RT3000 units, including RT2000, RT4000 and Survey+
Things to remember
To configure both base station corrections and NTRIP on the xNAVs and AV200, you will need to use the Serial Input tab on Interfaces to select GNSS differential corrections. From here you can then select the correction format and whether NTRIP is in use.
When you are not able to get into a differential position mode (RTK integer, RTK float, Differential), you may want to troubleshoot whether the radios are communicating. This article is intended to ensure there is communication at the hardware level.
Radios that are mentioned in this article:
- Satelline EASy (manual attached)
Step 1 - Frequency
Step 2 - Baud Rate
There is a chain of four items which must all have the same baud rate - the base station, the sending radio, the receiving radio and the mobile station.
|OxTS devices (RT3003 etc.)||9600 bps by default|
|NovAtel devices (PwrPak7 etc.)||19200 bps by default|
Step 3 - Operating Mode
- Setup (Right button)
- -> Additional (Use up/down buttons to find)
- -> Priority(Check that it says RX/TX)
- -> Additional (Use up/down buttons to find)
Step 4 - Serial Connectors
The link between radio and receiver is a serial connection, which has many possible configurations. It is important to find the user manual and check that the pins on all cables match up with what you need.
|Satel EASy radio||DB15 female (in)|
|FreeWave FGR2 radio||DB9 female (in)|
|GNSS Receivers / INS Devices|
|RT3003G INS||DB15 male (out)|
DB9 male (out)
Communicates to radio through COM2 port
|PwrPak 7 Receiver||
DB26 male (out)
N.B. - supplied with COM1 only cable with a DB9 female ending (can be tricky)
|Unit||Likely use case||Check for|
|PwrPak7 direct connection to RT3003G||14C0097A cable in between||Power provision and data pins 2 and 3|
|PwrPak7 connection to Satel radio||Gender changer to fix the female end connector||Mirroring the pins (2 and 3) rather than being carried through|
Step 5 - Error Correction Settings
Make sure that the error correction settings are not drowning out any desired signals - if in doubt, turn this feature off on both radios to see if the problem is fixed.
Step 6 - Sanity Check
If the radio still is not working, try using a third radio to check for shorted or otherwise damaged serial connectors. It is recommended to cut the power before removing serial connectors to prevent any electrical faults, so this may have occurred before you acquired the radio.
Satel Radio LED Definitions
|Request To Send||Clear To Send||Transmitting Data||Receiving Data||Carrier Detect|
|Off||Red||Off||Off||Off||Idle - No data transmission at all|
|Off||Red||Off||Off||Red (constant)||RSSI threshold possibly set too low|
|Transmitting a data packet|
|Off||Red||Off||Off||Orange||Noise or other transmission on this frequency|
|Off||Red||Off||Green||Green||Receiving a packet|
Freewave Radio LED definitions
|Base CD||Base TX||Base CTS||Mobile CD||Mobile TX||Mobile CTS||Descriptions|
|Red||Red||Red||Red||Off||Red flash||Power no link|
|Green||Slow red flash||Slow red flash||Green||Slow red flash||Slow red flash||Linked|
Carrier Detect Line
The "Carrier Detect" (CD) LED refers to a signal from the radio modem to the DTE (Data Terminal Equipment). It indicates whether there is activity on the radio channel - it is active whenever a signal exceeding the level required for reception exists on the radio channel, or when the radio modem itself is transmitting.
It does not make any difference if the signal is an actual data transmission, a signal of a radio transmitter not belonging to the system, or even an interference signal.
RSSI, or “Received Signal Strength Indicator,” is a measurement of how well your device can hear a signal from an access point or router.
Because an RSSI value is pulled from the client device’s WiFi card (hence “received” signal strength), it is not the same as transmit power from a router or AP.
Common issues with using NTRIP for differential corrections using the serial interface
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 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:
- The Enable NTRIP checkbox is ticked
- The correction format is the same as that used by the NTRIP provider
- 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, 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.
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.
Using a xNAV and AV200 with a 15 pin radio
If using a xNAV or AV200 the cable below is needed as the serial port on these units does not provide power. This requires a 9-15 pin cable to connect the 15 pin radio to the 9 pin RS-232 port on the user cable.
It is also possible to use the 9 pin serial port on the RT3000 and RT1003 to connect to the radio. Please refer to the follow guide.
Using the J2 Serial connector as access point for Differential corrections
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?
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