What is the Trimble EM940 Dual Band Radio Module?

The Trimble EM940 dual band radio module is one of the most exciting radio products that Trimble has released in over a decade!  The EM940 adds the ability  to receive both 900 MHz and UHF (410 MHz 470 MHz) corrections to almost any Trimble RTK enabled GPS / GNSS receiver. 

The EM940 is especially useful when buying used Trimble GNSS receivers because it removes the need for the GPS receiver to already have an internal radio installed.

Multiple Frequency Bands

Dual band configuration offers the flexibility to receive RTK corrections from either 900 MHz or UHF (410 MHz - 470 MHz) local base stations.  This is very useful for surveyors, contractors and mining operations where machine control systems like GCS900, Accugrade and Earthworks systems might be operating off of a 900 MHz base station while survey is running a separate UHF base station. 

The EM940 radio module offers multiple radio protocols making it compatible with most base station corrections - even if the base station is a Topcon, Leica or other brand.

Compatibility

The EM940 is part of Trimble's Empower line of wireless products.  It requires a controller that includes the Empower bay and is secured in place by two screws.

• TSC5 / Ranger 5
• TSC7 / Ranger 7
• T100
• T7 / Yuma 7

On the field software side, the EM940 is compatible with:

• Trimble Access ver. 2022.11
• Trimble Siteworks ver. 1.60
• Spectra Geospatial Origin (same version as Access)

Datasheets: EM940 | EM450 | EDB10 Data Bridge 

EM940 Limitations

It's important to note that the Trimble EM940 is a "receive only" radio - meaning it cannot be used to transmit RTK corrections. 

In some countries where 900MHz radios are restricted, Trimble offers the EM450 which offers UHF reception only. Those countries currently include: South Africa, Thailand, South Korea, and the UAE.

For controllers without the Empower bay, you'll need the EDB10 Data Bridge.

900 MHz vs UHF

The purpose of the radio is to transmit corrections from your base station to your rovers. Receiving corrections from your base station enables your rovers to achieve centimeter level precision. The radio frequency at the base station must match the radio frequency in the rovers.

Some base stations are configured to also transmit over the internet, requiring an internal cellular modem or phone to receive corrections at the rover.

900 MHz radios are license free and typically found in Trimble construction and agriculture systems.  900Mhz radios are low power and better suited for job sites, subdivision projects, farms and mines because they have a typical range of 3 to 4 miles. For corridor / roading projects a 900 MHz repeater radio can be used to increase distance from the base station. 

UHF radios provide corrections between 403 MHz to 470 MHz.  UHF stands for Ultra High Frequency which is managed in the United States by the FCC (Federal Communication Commission) and require a license to transmit - You do not need a license to receive UHF corrections.

UHF radios range in power from .5 Watts to as high as 35 Watts.  The high power configuration can transmit over 20 miles so they are very useful in rural areas, boundary surveys, long roading and infrastructure projects.  UHF repeater radios can be used to increase distance but also complicates configuration. 

Looking for used Trimble RTK systems? 

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