Free RTK Corrections for Your Tractor

The autosteer kit was a one-time purchase. The corrections that keep it on the line are the bill that never ends — commercial RTK networks charge by the year, per machine, so the bill grows with every tractor, sprayer, and combine you put on the network. The corrections themselves are not the expensive part: if you own a GNSS base station, or are willing to put one up, centimeter accuracy for every machine you run costs nothing per month.

Where free corrections actually come from

Three real options, in rough order of how much control you get:

• Your state's CORS network. Many states run free NTRIP casters off their public reference stations. If one sits close to your fields, it's a genuinely good answer — check the coverage map first, because stations cluster around towns and highways, and RTK performance falls off as the distance to the base grows.
• RTK2go. The big free public caster. If a neighbor already shares a base near you, you can ride it today. But it's a stream you don't control: no guarantee it's up during planting, no say in how it's configured, and if the owner unplugs it, your guidance goes with it.
• Your own base. A receiver and antenna on a shed roof or a fence post, surveyed once. Shortest distance to your fields, no dependence on anyone else — and because the reference point never changes, your AB lines come back exactly where you left them, season after season.

This post is about the third option, because it's the one that pays off every year you farm.

What AgOpenGPS actually needs

AgOpenGPS speaks NTRIP out of the box — its comms app (AgIO) has an NTRIP client built in, and it asks for exactly four things: caster address, port, mountpoint, and a login. Fill those in and corrections flow to the receiver on the tractor, the receiver reports an RTK fix, and the steering does the rest. Other autosteer systems with an NTRIP or "custom network" option take the same four fields.

The catch is where those four fields point. The DIY instructions that circulate say: run caster software on an always-on PC at the farm, forward a port on your router, and hope your internet has a public address. On a rural connection — cellular or Starlink — that last part usually ends it: carrier-grade NAT can't accept inbound connections at all.

A hosted caster removes that whole problem. Your base makes one outbound connection to a private mountpoint on RoboGNSS, and outbound works through any router or cell modem. The tractor connects to the same caster from the other side. Nothing at the farm serves anything.

The setup, start to finish

Budget an afternoon, most of it on the roof.

1. Put up the base. An F9P-class receiver (ArduSimple and SparkFun boards are the community favorites), a decent antenna with clear sky view, and an internet connection. If you're starting from zero, our 7-step base station build walks through the hardware.
2. Create the base station on RoboGNSS. The free plan covers one base — declare its surveyed position and datum (the caster continuously checks what your receiver broadcasts against it) and copy the upload token.
3. Point the receiver at your mountpoint. In its NTRIP server settings, enter your RoboGNSS mountpoint, port, and token. NTRIP v1 and v2 are both accepted, so anything from a bare F9P to a WiFi NTRIP Master accessory works.
4. Mint a credential for the tractor. Each machine gets its own login to the stream — revocable one by one, so lending corrections to a neighbor doesn't mean sharing the password to everything.
5. Enter the four fields in AgIO, start the stream, and watch the fix quality go to RTK. That's the whole client side.

From then on the base runs itself, and the live health view — uptime strip, satellite counts, position checks — tells you it's working before you're sitting in the cab wondering why the fix dropped.

More than one machine

The free plan includes two rover credentials with two simultaneous connections — a tractor and a sprayer, or your machine and a neighbor's. When the operation outgrows that, Pro ($9/month) raises it to 10 rovers per base, and Fleet ($29/month) runs 10 bases with 25 rovers each — enough to cover every machine and every farm you touch. There are no per-rover or data charges on any plan; the connection caps are the whole story.

What it costs, honestly

• The base hardware, once. Receiver, antenna, mount, and a power supply — a few hundred dollars for the F9P-class builds most AgOpenGPS people run. If you already built a base, this line is zero.
• Internet at the base. The stream is small; any connection that can hold a phone call can carry it.
• The caster: free. One base station, two rovers, live health, and seven days of raw data downloadable as RINEX — free forever, not a trial.

Compare that with a correction subscription billed per machine, every year, whether it rained or not. The base pays for itself the first season, and unlike a subscription it's an asset: the same station can also earn on Onocoy without giving up your own RTK if you later put it on a paid plan with forwarding.

Start with a free base station — and if you're currently running caster software on a PC in the shop, the SNIP migration guide covers moving that setup to the cloud too.