Set up an RTK base

The base is the receiver that sits still on a tripod and sends corrections to the receiver on your machine. Your own base is the most reliable source of corrections: you decide where it stands and how far away it is, and there's no subscription. (New to these words? Start with How RTK works.)

Set it up well once, keep putting it in the same place, and most RTK problems never happen. This page covers any base; the app steps for an Emlid Reach base are at the end.

Before you start

Time: allow about 15 minutes the first time. After that, an averaging base needs two minutes each time you switch it on.

• A base receiver and a rover that work together (for Emlid Reach: two RS3 or RS4 receivers)
• A tripod (with an extender, if you have one) or a fixed mount
• Power for the base from outside: a base power cable to a 12 V battery, or a USB power bank
• The radio frequency you'll use, the same on the base and every rover
• A benchmark on the field you'll work, or a plan to set one (see Benchmarks and calibration)

1. Pick the spot

   Find open sky all the way round, from about 15° above the horizon upward. Stay away from buildings, grain bins, trees and metal sheds: they block the signals or bounce them.

   Go high enough that the radio has a clear path across the fields you'll work. Keep the machine within 2 miles of the base, with nothing blocking the view between them.

   Pick a spot you can come back to exactly: beside the yard light pole, a corner post, a pin in the ground. The point is to stand the base in the same place every time.

2. Mount it so it can't move

   Use a tripod over a marked point, set firmly with the legs spread and pushed in, or a fixed mount on a post or roof. The base must not move, tilt or settle while you work. A tripod bumped by a cow, the wind or a pickup has moved, and so has every elevation the rover reports.

3. Power it from outside

   Plug in the base power cable to a 12 V battery, or a USB power bank. A base sends corrections all day, so don't count on its own battery. An Emlid Reach's internal battery lasts about a working day as a rover; a base should run on outside power.

4. Choose: average each start, or a known point

   The base has to know its own position before it can correct anyone else's. There are two ways:

   • Average each time it starts. The base works out its own position over two minutes every time it's switched on (on an Emlid Reach: Average SINGLE, 2:00, which is what the app sets). Simple, but each start averages a slightly different position, so elevations shift from one day to the next. You calibrate to a benchmark every time the base restarts.
   • A known point. You type in the coordinates of a surveyed mark and set the base exactly over it (on an Emlid Reach, a manual coordinates entry in Emlid Flow's base settings). The base then starts the same way every time, as long as it really is over that mark. Setting up the base from the app puts it back to averaging, so type the known point in again afterwards if you use one.

   Antenna height doesn't matter for Ditch Assist®: leave it as it is. Calibrating to your benchmark takes care of it.

5. Set the radio

   Put the base and every rover on the same frequency and air data rate. On an Emlid Reach: LoRa radio, a frequency between 902 and 928 MHz, 18.23 kb/s. An RS4 base sends at 500 mW, or 1000 mW when you need more range. An RS3 always sends at 20 dBm, its maximum.

6. Switch the base on and wait

   An averaging base sends nothing until it has finished averaging: two minutes on a Reach set up by the app. Then switch on the rover and watch the GPS badge climb to a green RTK.

7. Calibrate to your benchmark

   Before you survey or grade against work from an earlier day, drive to the benchmark and calibrate. That lines today's readings up with your saved surveys and designs. See Benchmarks and calibration.

Same base, same spot

Make it a habit: the base goes up in the same place, on the same mount, every day. Even then, an averaging base starts a little differently each time it's switched on, so:

The benchmark is what makes this work: a fixed point in the field (a post, a gate corner) with a saved elevation you can always come back to. See Benchmarks and calibration.

Set up an Emlid Reach base from the app

The app's Emlid Diagnostics does it in about five minutes. First, with the tablet on the base's Wi-Fi, follow Check and program a Reach with Emlid Diagnostics up to and including the step Tap Configure. Then make the base choices below.

Then set up each rover on the same frequency: join the rover's Wi-Fi, open Emlid Diagnostics again, and set it up as Rover (control module or DIG) or Lite Rover (Ditch Assist Lite). Every tap is on Check and program a Reach with Emlid Diagnostics.

Setting up a base by hand in Emlid Flow? Follow the RTK base steps in the receiver setup guide. A finished base reads:

If it doesn't work

• The rover never gets past GPS: the base isn't sending. Is it powered, done averaging, and on the same frequency? On a Reach, Base output 1 must read LoRa radio. Corrections troubleshooting.
• The base's LoRa radio output won't turn on: the radio can't carry the messages once a second. The app lowers the rates for you.
• The fix drops to Float far from the base: move the base higher or closer; on an RS4, switch to 1000 mW. Stuck on Float.
• Elevations are off by the same amount everywhere: the base moved or restarted. Calibrate to your benchmark. Grade is off.
• The base battery dies mid-day: run it on outside power.