Clear all

CHC x91 and X900s-Opus RTK GCP solution?

FNG Member

Greetings - 

Using the instructions seen here >

And the CHC GNSS base stations, (X91 and X900s Opus) with the supplied Windows Mobile PDA, SurvCE software, my goal is to create a high quality UTM WGS84 georeference control point in the sub 20cm of global accuracy or less range. The narrower the better. 

Although I can connect to either device, specify settings, and run a survey with a good satellite constellation, I am only ever receiving data from one rover at a time in Autonomous mode.

A solution is never fixed, (only Autonomous status of collection) and I am unable to get both devices on the same frequency to speak together in an RTK solution.

Because of this issue I am only ever seeing accuracy in the ~2 meter range, which is not sufficient.

From my understanding the X900s-Opus may not be capable of true RTK work and may not be capable of communicating with the X91 and correcting. That said, the X91 should be capable. 

I tried reconfiguring the Frequency settings for both X91 and X900-opus in the CHC Configure tool to be on same band and protocol for bluetooth connectivity, but after setting and opening up the SurvCE software the same frequencies are not available for either device and hence no communication occurs. When i try to reset the frequency manually it does not save to the device.

Alternatively, when I try to use the LT30 GPS handheld terminal for cellular or TCP/IP RTK, the system requests information about a NTRP caster for internet RTK. In the past I have used the CORS base station TIBB (   for corrections in inertial explorer, but this process is largely automated and I am not sure how to configure this.

If this cannot be settled, I would like to know if there are any resources about recording a Raw GPS stream from one of these types of base stations for ingestion into Novatel's Inertial explorer post-processing software.(File formatting, etc)

I am new to surveying with these types of ground control base stations and have only used LidarUSA's Snoopy type devices (Novatel IMU+Pinwheel GNSS receiver) for Inertial Explorer in the past.

This is a lot of information, so I appreciate anyone who takes the time to sort through it and attempt to generate some understanding!

Topic starter Posted : September 28, 2020 9:12 pm
Topic Tags
1,000+ posts Supporter

@mark-silver should be able to assist.  I will save and follow this thread - good stuff. 

Posted : September 29, 2020 3:23 am
200+ posts Member

Can the 900 transmit? No firsthand knowledge but, I thought the 900 was a static receiver, only. 

If the 900/91 are able to serve as base-rover, you should find success diligently following the steps beginning on page 20 of the linked manual. Use Carlson on your DC to set things ups... shouldn't need windows, at all.

Additional Caveat- I work in state plane so, not sure if you can pull directly to WGS. Might take some post processing. First you need to know if your pair will talk and I don't have that answer.

Good luck,

Posted : September 29, 2020 8:31 am

200+ posts Member

Perhaps it's similar to the IG3 setup?


Though, this FAQ seems to suggest you can't use it as an RTK base:


  1. What are the differences between the X90D-OPUS (original static receiver) and the iG4?Here is a list with explanations:

iG4 tracks 384 channels instead of 24, more is better of course
iG4 is smaller and lighter weight
iG4 has Bluetooth and works as an RTK Base
iG4 tracks GLONASS, Galileo and BeiDou, this helps the receiver continue to track under heavy canopy
iG4 comes in a smaller hard case, easier to pack, costs a little less to ship
iG4 charger holds 4 batteries instead of 2
iG4 battery is qty 1 3,400 mAh instead qty 2 2,200 mAh (we only ship one battery standard now)
iG4 runs longer on the new battery than the X90 ran, however the iG4 does use more power
New 3,400 mAh batteries are $120 instead of $90 for 2,200 mAh
iG4 battery is shipped discharged and inside the head (because of new shipping regulations)
iG4 MSRP costs $2,400 instead of X90-OPUS $2,450 MSRP (however the street price is probably more)
iG4 includes Ground UPS shipping instead of 3-Day Select (required because of new shipping regulations)
The new optional 2-meter heavy duty cable is only $100 instead of $146

Posted : September 29, 2020 9:25 am
FNG Member

My understanding is that the X900s-Opus is not capable of RTK, but the X91 Should be. 

In this case I would be dependent upon some post processing from a remote station since the x900s doesn't suffice as a partner, (hence discussion about NTRP caster for internet RTK or Novatel Inertial Explorer). 

Has anyone ever successfully recorded raw GPS with either of these stations for intake into Novatel's software? I am very familiar with the software but not so sure about whether the CHC devices are capable/compatible. 

I can always reach out to Novatel in this case, but I thought members of this forum may have been of assistance. 

Topic starter Posted : September 29, 2020 11:53 am
Mark Silver
500+ posts Vendor

X900S was a Static receiver. However it accidently would run as a 'Data Collector Internet' RTK Rover. But the main intention was to produce static RINEX files.

The X91+ will run RTK. 

We spoke yesterday and this morning at some length, but don't hesitate to call us (iGage) if additional questions.

Posted : September 30, 2020 12:28 pm
Jaccen and Brad Ott liked