How Northing RTK works: centimeter corrections through your phone

Satellite positioning on its own is accurate to a few metres. The error comes mostly from the atmosphere and from small imperfections in satellite clocks and orbits — and because those errors are measurable, they are correctable. Northing RTK is the correction side of the system: a live data stream that lets the receiver turn metres into centimeters.

This guide covers what that stream contains, the path it takes to reach the receiver, how fast the result arrives, and what happens when part of the chain breaks.

What a correction stream actually contains

It is not a position. A common misconception is that some server knows where you are and sends you a better answer. Nothing in the chain knows or needs to know where you are.

What the stream carries is a description of the errors in the system right now: refinements to each satellite’s clock and orbit, and a model of the ionospheric and tropospheric delay across the region. Your receiver takes its own raw measurements — its own timing, its own carrier phase — and applies those refinements locally. The position is computed in the device on your roof, from your own observations. The stream just removes the lies in the inputs.

Two consequences follow, and both matter:

• Your position never leaves the receiver as a condition of getting corrections. The correction data is broadcast-shaped, not a request-and-answer about you.
• The stream is tiny. Describing a handful of satellites’ errors takes far less data than describing a position ten times a second. In practice it runs at roughly 1 kbps.

No base station, no radio, no second data plan

Classic RTK needs a reference station near you — your own, or a network’s — plus a radio link to carry its corrections to the rover. That is a real piece of infrastructure: a tripod that has to be surveyed in accurately, a power supply, a radio pair with licence and range limits, and someone to notice when it stops.

Northing RTK works differently. Corrections are modelled across entire continents and delivered over the internet, so there is nothing on your side to set up, survey in, power, or maintain. The trade is that you need a data connection — which is where the phone comes in.

Why the phone is the right place to put the connection

The phone in your pocket is already a well-maintained, well-powered modem with a screen, and you already pay for its data. Putting a second cellular radio in the receiver would mean a second SIM, a second bill, a second thing to roam badly abroad, more power draw on the roof, and another radio to certify in every market. So the receiver does not have one.

Instead the app relays the stream to the receiver over Bluetooth Low Energy, at roughly 1 kbps. That has three practical consequences worth stating plainly:

• It works on one bar. A correction stream is a trickle; it survives connectivity that would make a video call unusable.
• It costs a few megabytes a day, not hundreds.
• Your phone is the monitor. Position, fix type, satellite counts and health come back over the same link, so any app can show them without a proprietary terminal on the dash.

What it does in practice, measured

We publish measured behaviour rather than adjectives. These numbers come from logged dual-receiver drive sessions, each with the condition it was measured under:

• Fixed within seconds of a cold start. RTK does not converge; it fixes. There is no ten-minute warm-up before work can begin.
• ±2.5 cm repeatable accuracy while fixed, open sky.
• Fixed for 88% of a 40-minute drive that deliberately included tree cover, a bridge, and buildings — with 1–2 second recovery after each obstruction.
• A one-minute data dropout is a non-event. The receiver held centimeter accuracy for about a minute unaided, degraded gradually rather than falling off a cliff, and was back to RTK-Fixed 24 seconds after the stream returned.

The 88% is the number a brochure would leave out. It is there because a 40-minute drive with deliberate obstructions is a fair test and 100% would be a lie: hedgerows and bridges cost you satellites, and no correction service can send you a satellite you cannot see.

Fix states, and what each one is telling you

The app shows a fix type, and it is worth two minutes to learn to read it, because it is the difference between trusting a pass and redoing it.

• No fix / 2D. Not enough satellites yet. Normal for a few seconds after power-on, or under a shed roof.
• 3D fix. An ordinary uncorrected position — metres. This is what a phone gives you all day.
• Float. Corrections are arriving and being applied, but the receiver has not yet resolved the whole-cycle carrier-phase ambiguities. Accuracy is typically decimetres and improving. Float is a transitional state, not a destination.
• Fixed. The ambiguities are resolved. This is the ±2.5 cm state, and it is the only one to plan repeated passes around.

The distinction that matters is float versus fixed. A float solution looks plausible on screen and is not repeatable at centimeter level; work laid out on float and rechecked later will not line up. A well-behaved receiver in open sky moves through float to fixed in seconds, so if it sits in float, something is wrong upstream — usually sky view, occasionally the correction stream.

Correction age: the number worth watching

Alongside the fix type, the receiver reports correction age — how long ago the last usable correction arrived. In healthy operation it sits at a few seconds and stays there. Rising age is the earliest visible sign that the data path is in trouble, well before the fix type degrades.

That is because the receiver does not fall over the moment the stream stops. Corrections describe conditions that change slowly, so a slightly stale correction is still mostly right; the accuracy decays as it ages rather than vanishing. Our dropout testing put roughly a minute of usable centimeter accuracy on that decay before it became visible in the position, and 24 seconds to recover once the stream came back.

An age that climbs and then resets is a phone that briefly lost signal. An age that climbs and keeps climbing is a connection that needs attention — and after 30 seconds the receiver stops being subtle about it.

The honesty feature

GNSS engines have an ugly habit. When a correction stream dies silently — the phone drops off the network, an app is killed in the background, a cable works loose — many engines keep reporting centimeter confidence while the true error quietly drifts. We measured exactly that: quality flags, accuracy estimates, and correction-age fields all frozen while the real error grew from 7 cm toward 40 cm.

That failure mode is worse than plain inaccuracy, because it destroys your ability to know which work to trust. So the receiver runs its own independent watchdog: if corrections stop flowing for 30 seconds, it flags “Stale Corrections” to every connected app, whatever the engine underneath claims. You find out that the data connection needs attention before a pass goes crooked, not after.

There is more on the receiver-side design in inside the receiver.

What actually happens the first time

There is no commissioning procedure, because there is nothing to commission.

1. Mount and power the receiver. 5 V USB, somewhere with a clear view of the sky — roof, bar, or pole.
2. Pair it in the app. Bluetooth pairing, once. The receiver has no keypad and needs no network credentials of its own.
3. The app starts relaying corrections. Nothing to type: no correction server address, no mount point, no port, no username and password. If you have ever configured an NTRIP client at the edge of a field with cold hands, that omission is the entire point.
4. Watch it fix. Seconds, in open sky.

No base station to survey in, no radio pair to align, no dealer visit, and no calibration drive. The receiver is also the thing that gets better over time: firmware updates arrive over the air, signed, with automatic rollback if one misbehaves.

Where it works

Northing RTK is a modelled service with real boundaries, and we would rather you knew them before buying than after. It covers the contiguous US and Canada, most of Europe, Japan, South Korea, New Zealand, Brazil, and parts of Australia. It does not cover Alaska, Hawaii, or the US offshore territories, and Australian coverage is partial in exactly the places broadacre work happens.

The map and the gaps are in the coverage guide, and your location is checked against current coverage at checkout — if the service cannot serve your fields, we say so before you pay.

Outside coverage the receiver still works: Northing Global, the free mode built into every unit, has no zones at all. It is slower to settle and less accurate, and the honest comparison is in RTK vs PPP.

One flat price

Northing RTK is included for the receiver’s first year, then renews at a flat $299 for 12 months. No per-hour metering, no usage tiers to predict, a reminder email before every renewal, and a fair-use ceiling stated in plain English in the terms. Cancel and the hardware keeps working — see the pricing for the whole of it.