How to Configure NTRIP on a GNSS RTK Receiver: 2026 Guide
You have just received your APEKS RTK receiver. The battery is charged, the pole is assembled — and the controller is showing Single solution despite the CORS credentials being entered. NTRIP configuration looks straightforward but has several steps where small errors — a wrong APN, a copied password with a hidden space, a mountpoint 40 km further than the nearest one — silently prevent connection or degrade accuracy without any obvious error message. This guide covers the complete NTRIP setup process from SIM card insertion to confirmed Fixed solution, including country-specific CORS server addresses for the key markets where APEKS receivers are deployed: Indonesia, Saudi Arabia, South Africa, Brazil, Turkey, and Egypt. Whether you are configuring NTRIP for the first time or troubleshooting a connection that stopped working in the field, this guide gives you every setting in one place.
What Is NTRIP and How Does It Work?
NTRIP — Networked Transport of RTCM via Internet Protocol — is the standard method for delivering GNSS differential corrections from a CORS (Continuously Operating Reference Station) network to a rover receiver via mobile internet.
How it works:
- The CORS network operator runs a server — the NTRIP Caster — that collects real-time correction data from reference stations and makes it available over the internet.
- Your APEKS receiver (the NTRIP Client) connects to the caster via the built-in 4G modem, authenticates with your credentials, and selects a correction stream (mountpoint) from the nearest reference station.
- The caster streams RTCM correction messages to the receiver continuously. The receiver applies these corrections to its raw GNSS observations to compute a centimetre-accurate Fixed RTK position.
Key terms to know:
- Caster: the NTRIP server operated by the CORS network.
- Mountpoint: a specific correction stream, usually named after the reference station location.
- RTCM: the standard correction message format (3.0, 3.2, 3.3).
- Differential age: the time since the last correction message was received — must stay below 3 seconds.
What You Need Before Configuring NTRIP
1. Active SIM Card
The SIM must support data (not voice-only). For international deployments, confirm the SIM has roaming data enabled or use a local SIM purchased at the project country. Recommended data plan: at least 1 GB/month per active receiver. NTRIP consumes approximately 5–15 MB/hour depending on correction format.
2. CORS Account Credentials
Username and password from the national or commercial CORS network operator. In most countries, CORS accounts are obtained from the national mapping authority or a licensed private network operator. Keep credentials in a secure note — do not store them in plain text on the controller.
3. Server Address and Port
The NTRIP caster address for your country's CORS network. Default port is 2101 for most national CORS networks. Port 80 is used by some commercial networks. Port 443 is used by networks that require HTTPS.
4. APEKS Receiver with Built-in 4G
AP20 and above include a built-in 4G modem. AP10 can connect via Bluetooth to a smartphone acting as a mobile hotspot.
SIM Card and APN Setup
The SIM card slot is located under the battery compartment on all APEKS GNSS receivers. Use a nano-SIM. Power off the receiver before inserting the SIM. Power on and allow 30 seconds for the modem to register on the network. The network status indicator in ApekSurv → Device Status should show signal bars and the operator name.
In ApekSurv → Device Status → Network, confirm the data connection status shows "Connected" and an IP address is assigned. If not connected, proceed to APN configuration.
If the receiver cannot connect automatically, go to ApekSurv → Settings → Network → APN and enter the APN manually. The APN is provided by your SIM card operator. Common APNs: Indonesia Telkomsel = internet; Saudi Arabia STC = jawalnet.com.sa; South Africa Vodacom = internet; Brazil TIM = tim.br; Turkey Turkcell = internet.
Open a browser on the connected controller and confirm internet access. If the controller cannot reach any website, the SIM data issue must be resolved before NTRIP will work. NTRIP requires a working data connection — it is not a substitute for it.
Step-by-Step NTRIP Configuration in ApekSurv
In ApekSurv, tap the satellite icon or go to Device → Data Link → NTRIP Client. The NTRIP configuration screen displays fields for server address, port, username, and password.
Type the NTRIP caster address for your CORS network. Do NOT paste from email or messaging apps — hidden formatting characters silently break the connection. Type manually, character by character. Port is typically 2101.
Type username and password exactly as provided by the CORS operator. Credentials are case-sensitive. A single capital letter difference or trailing space causes authentication failure with no clear error message.
This fetches the list of available mountpoints from the caster. If this step fails (timeout or empty list), the server address or port is wrong, or the data connection is not working. Do not proceed until the source table loads successfully.
Choose the mountpoint corresponding to the reference station geographically nearest to your survey location. Confirm the format shown (RTCM3.x is preferred over RTCM2.x or CMR).
ApekSurv establishes the NTRIP connection. The status indicator changes from "Disconnected" to "Connected". Differential age begins counting from 0.
Watch the solution status in the ApekSurv status bar. Within 10–30 seconds on open sites, the status should change from Single → Float → Fixed. If Fixed is not achieved within 2 minutes, check differential age and mountpoint distance.
Selecting the Right Mountpoint
The mountpoint determines which reference station's corrections your receiver uses. Selecting the wrong mountpoint is one of the most common causes of Float solution or degraded accuracy — even when the NTRIP connection shows as active.
How to choose:
- Select the mountpoint named after the nearest town, city, or station to your survey location.
- If multiple mountpoints are listed and you are unsure which is nearest, check the source table for coordinates — most CORS networks include the station latitude and longitude in the source table.
- Prefer RTCM3.2 or RTCM3.3 format over RTCM2.x. RTCM3.x supports multi-constellation corrections (GPS + GLONASS + BeiDou + Galileo). RTCM2.x is GPS-only.
- Prefer VRS (Virtual Reference Station) or MAC (Master-Auxiliary Concept) mountpoints where available — these are computed correction streams that account for your specific location within the network, rather than raw corrections from a single physical station.
Maximum baseline guideline: Most CORS networks guarantee ±10–20 mm horizontal accuracy within 50 km of the reference station. Beyond 70 km, atmospheric decorrelation typically prevents reliable Fixed. If your nearest mountpoint is more than 50 km away, deploy an APEKS local base station instead.
Understanding Differential Age
Differential age is the number of seconds since the receiver last received a valid correction message from the NTRIP caster. It is displayed continuously in ApekSurv's status bar.
What the values mean:
- 0–3 seconds: normal operation. Corrections are current. Full RTK accuracy applies.
- 3–10 seconds: marginal. Accuracy begins to degrade. The receiver extrapolates corrections. Results still usable for earthworks but not for structural survey.
- 10+ seconds: corrections are stale. The receiver may drop to Float. Do not record precision points.
- Connection lost: differential age stops updating and the solution drops to Single. ApekSurv shows "Disconnected" in the data link status.
If differential age regularly exceeds 3 seconds on a site with good cellular signal, the CORS network may be experiencing server load or the mountpoint may be oversubscribed. Switch to an alternative mountpoint or reduce the polling interval in ApekSurv settings.
NTRIP Settings by Country
The following table covers NTRIP server settings for the primary markets where APEKS receivers are deployed. Credentials must be obtained separately from each network operator — the table provides server addresses and ports only.
| Country | CORS Network | Server Address | Port | Notes |
|---|---|---|---|---|
| Indonesia | BIG InaCORS | cors.big.go.id | 2101 | Free registration at big.go.id |
| Saudi Arabia | NGOSA | ngs.ngosa.gov.sa | 2101 | Ministry of Survey credentials required |
| South Africa | TrigNet | ntrip.trignet.co.za | 2101 | DALRRD registration required |
| Brazil | IBGE-RBMC | 200.144.244.237 | 2101 | Free registration at ibge.gov.br |
| Turkey | TUSAGA-Aktif | www.tusaga-aktif.gov.tr | 2101 | Paid subscription; HGK credentials |
| Egypt | EGSA CORS | Contact EGSA directly | 2101 | Credentials via national mapping authority |
| UAE | DLS CORS | Contact Dubai Land Dept | 2101 | Project-specific access |
| India | NavIC/CORS | State-level networks vary | 2101 | Check state survey department |
Note: Server addresses are subject to change. Always verify with the national mapping authority before deployment. APEKS regional support can assist with CORS configuration for Belt & Road project markets.
Common NTRIP Configuration Errors
Symptom: Tapping "Get Source Table" returns timeout or empty result.
Cause: Wrong server address or port, or no data connection. Hidden characters in copy-pasted address.
Fix: Retype server address manually. Confirm port is 2101. Test data connection by opening a browser on the controller.
Symptom: Source table loads but connection fails with "Unauthorised" or "401" error.
Cause: Username or password entered incorrectly. Credentials are case-sensitive. Trailing space is invisible but breaks authentication.
Fix: Delete and retype credentials character by character. Confirm account is active with CORS operator. Some networks require account activation before first use.
Symptom: NTRIP shows Connected and differential age is below 3 seconds, but solution stays Float after 2+ minutes.
Cause: Mountpoint is too far away (>70 km), or RTCM2.x format selected instead of RTCM3.x, or sky obstruction preventing enough satellites for Fixed ambiguity resolution.
Fix: Select a nearer mountpoint. Switch to RTCM3.2 or RTCM3.3 format. Move to a location with better sky view.
Symptom: Connection is active but differential age regularly jumps above 5–10 seconds.
Cause: Poor cellular signal at the survey site, or CORS server congestion on the selected mountpoint.
Fix: Check cellular signal strength in ApekSurv → Device Status. Switch to a different mountpoint on the same network. If cellular coverage is inadequate, deploy a local APEKS base station instead of relying on NTRIP.
FAQ
Can I use NTRIP with a smartphone hotspot instead of the built-in SIM?
Yes. The APEKS AP10 and any APEKS receiver can connect to NTRIP via a smartphone hotspot. Connect the receiver to the phone's Wi-Fi hotspot in ApekSurv → Settings → Network → Wi-Fi. Then configure the NTRIP client as normal. This is useful when a local SIM is not yet available or when testing CORS credentials before a deployment. Note that hotspot connection adds a dependency on the phone's battery and signal — for production survey work, the built-in SIM on AP20 and above is more reliable.
How much mobile data does NTRIP use?
NTRIP correction streams consume approximately 5–15 MB per hour depending on the correction format and number of constellations. RTCM3.3 with full multi-constellation corrections uses more data than GPS-only RTCM2.x. A 1 GB data plan is sufficient for approximately 70–200 hours of active NTRIP connection — adequate for most monthly survey workloads. The receiver only downloads corrections when connected and surveying; idle time does not consume data.
Why does my NTRIP connection drop when I move between areas on the site?
NTRIP connections occasionally drop when cellular handover occurs between towers as you move. Enable auto-reconnect in ApekSurv → Data Link → NTRIP → Auto Reconnect. With auto-reconnect enabled, the receiver re-establishes the NTRIP connection automatically within 5–10 seconds of a dropout, typically without losing Fixed solution. If dropouts are frequent on a specific site, the cellular coverage may be marginal — consider deploying a local APEKS base station for that project.
What is the difference between NTRIP and a local base station for RTK corrections?
NTRIP delivers corrections from a permanent CORS network via mobile internet — no base station hardware required. A local base station is a second APEKS receiver you deploy on site, transmitting corrections via UHF radio or LoRa to the rover. NTRIP is faster to set up and requires no additional hardware, but depends on cellular coverage and the CORS network being within 50 km. A local base station works anywhere regardless of cellular coverage and is not affected by CORS network outages — but requires deploying and maintaining the base hardware. Most surveyors use NTRIP as the default and switch to a local base for remote or underground sites.
My CORS subscription expired mid-project. Can I continue surveying?
Without valid CORS credentials, NTRIP authentication will fail and corrections will not be delivered — the receiver will operate in Single solution only, with metre-level accuracy unsuitable for any precision work. Renew the CORS subscription before returning to site. As a temporary alternative, deploy any APEKS RTK receiver as a local base station to maintain centimetre-level accuracy while the CORS account is being renewed.
Related Articles
BUILT-IN 4G. GLOBAL CORS. ZERO GEO-FENCE.
APEKS receivers from AP20 onwards include a built-in 4G modem for direct NTRIP connection — no external dongle, no hotspot dependency. International firmware with no geo-fence restrictions means your CORS credentials work in Jakarta, Riyadh, São Paulo, and Istanbul on the same receiver.
View APEKS RTK Receivers →References
- RTCM Standard 10403.3 — Differential GNSS Services
- ISO 17123-8:2015 — Field Procedures for GNSS RTK
- BIG InaCORS Network — cors.big.go.id
- NGOSA CORS Network — Saudi National Survey Authority
- IBGE RBMC Network — ibge.gov.br
- TUSAGA-Aktif — HGK Turkey
- APEKS AP40 Laser+ Technical Datasheet, 2026
- ApekSurv Field Software User Guide, 2026