How to set up RTK over UHF radio

This guide explains how to send RTK corrections from your Reach RS3 base via the Harxon external UHF radio to your Reach RS3 rover with the built-in UHF radio.

Overview

By default, Reach RS3 can only receive corrections via the built-in UHF radio. Using the Harxon external UHF radio, you can set up your Reach RS3 as a base and send RTK corrections to your Reach RS3 rover with the built-in UHF radio.

To set up an RTK connection between two Reach RS3 units, you will need the following:

• Two Reach RS3 units
• Emlid Flow app
• UHF antenna for Reach RS3 rover
• Harxon external UHF radio (a radio device, a whip antenna, a power supply cable, a customized data cable)
• 12 V battery

Set up base

To set up your Reach RS3 as a base, you need to integrate it with the external radio first, configure base settings in Emlid Flow, and finish the setup by configuring the radio settings.

Integrating Harxon external UHF radio

To integrate your Reach RS3 used as a base with the Harxon external radio, follow the steps below:

1. Place your Reach RS3 on the tripod and make sure that it has a clear view of the sky and there are no obstacles nearby.

   note

   Learn more about placing your Reach RS3 in the Placement guide.

2. Place the external radio antenna on another tripod at a sufficient distance, approximately 1.5 m from Reach RS3 base.

3. Screw the antenna connector of the antenna cable into the antenna port on the radio.

4. Plug the 5-pin external connector of the customized data cable into the serial port on the external radio.

5. Plug the 9-pin external connector of the customized data cable into the EXT port on Reach RS3.

6. Plug the power supply cable into the power connector of the customized data cable.

7. Connect the clamps of the power supply cable to the 12 V power source.

Configuring base output in Emlid Flow

To send RTK corrections from your Reach RS3 base via external UHF radio, you will need to set it up as a base in Emlid Flow and configure the external radio settings. Follow the steps below:

1. Open the Emlid Flow app and connect to the Reach RS3 unit you want to use as a base.

   

2. Tap Settings and then select GNSS settings. Make sure you keep the default GNSS systems and update rate as shown in the screenshot below:

   

3. Go back to the Receivers screen and tap Base settings.

4. Select the base coordinates entry method.

   
   tip

   For Reach RS3, the antenna height is the distance from the mark on the ground to the center point on the Reach’s bottom (h in Figure 1), antenna reference point (ARP), plus the height of the receiver to the antenna phase center (APC), antenna height offset. Emlid Flow automatically adds the antenna height offset, which is 134 mm.

   note

   Learn more about base coordinates entry method and specifying base position in the Choosing base setup method guide.

5. Tap RTCM3 messages. Select the messages and set the update rates as on the screenshot below:

   

6. Go back to the Receivers screen and tap Base output.

   

7. Edit the settings for the serial port. Select the RS-232 port and set the baud rate at 38400. Tap Save.

   

After that, you need to configure settings on the integrated UHF radio.

Setting up corrections transmission over Harxon external UHF radio

To start sending corrections from your Reach RS3 base over the Harxon external UHF radio, follow the steps below:

1. Turn on the external radio by pressing the power button for three seconds.

2. Using the arrow keys, access and set the following settings:

   
   • Channel Frequency: Appropriate frequency for your region. In our case, we set 450 Hz.
   • Data Protocol: TRIMTALK
   • Radio Link Rate: 9600
   • Radio mode: Tx (transmitting)
   • Transmit power: *L
   • Serial Baud: 38400

Now you can proceed setting up your Reach RS3 rover.

Set up rover

To start receiving corrections on your Reach RS3 rover, you need to set up another Reach RS3 unit as a rover in Emlid Flow and configure its internal UHF radio to receive corrections from your Reach RS3 base. Follow the steps below:

1. Place your Reach RS3 rover on the survey pole and make sure that it has a clear view of the sky and no obstacles nearby.

   note

   Learn more about placing your Reach RS3 in the Placement guide.

2. Attach the UHF antenna.

3. Open Emlid Flow and connect to your Reach RS3.

   

4. Tap Settings and then select GNSS settings. Make sure you keep the default GNSS systems and update rate as shown in the screenshot below:

   

5. Go back to the Receivers screen and tap Correction input.

   

6. In the UHF cell, tap the Edit button. Set the same frequency as for the base, in our case it's 450 MHz, and set the bandwith at 25 Hz. The data rate will automatically change to 9600 bit/s. Tap Save.

   

7. Wait until your Reach RS3 rover starts receiving corrections and shows the FIX status.

   

Now you can enable tilt compensation and start surveying with your Reach RS3 rover!

tip

In this guide, we don't describe the process of enabling and initializing tilt compensation. Learn more about working with tilt compensation on Reach RS3 in the How to enable tilt compensation on rover guide.