RTK License Information
for Dealers and Customers in the United States

The Federal Communications Commission (FCC) recently completed a review of RTK GPS surveying operations in the United States (U.S.). The review was prompted by complaints that some RTK GPS surveying operations were interfering with co-channel voice users.

As the leading manufacturer of GPS surveying equipment, Trimble worked closely with the FCC to address the interference issue and to continue the RTK license process. While the outcome of the FCC review is favorable, it is important that Trimble and the RTK GPS community continue their educational efforts.

For its part, Trimble is committed to helping customers understand how to comply with the FCC rules.

To this end, Trimble has published RTK GPS Equipment User Responsibilities (pdf). This document provides guidelines for minimizing the potential for interference when operating Trimble GPS Total Station™ systems and details the penalties for failing to comply with the FCC rules.

Trimble has recently released the TRIMMARK™ IIe Base/Repeater radio modem, which automates two key operational requirements of FCC licensees known as "Listen Before Transmit" and "Station ID." Existing TRIMMARK II Base/Repeater units may be upgraded to the TRIMMARK IIe.

Background to the FCC Review

Most RTK GPS surveying equipment in the U.S. transmits data on frequencies between 450-470 MHz. These are shared frequencies, with voice communications having priority over data communications. FCC Rules 90.173 and 90.403 require licensees to cooperate in the shared use of frequencies in order to minimize interference and to take reasonable precautions to avoid causing interference.

The FCC received numerous interference complaints filed against existing licensees operating RTK GPS surveying equipment. These complaints are believed to have been triggered by two circumstances:

• RTK GPS users who are not monitoring their transmit frequency.
• RTK GPS users who select a frequency that serves as an input to a community voice repeater.

Interfering with a community voice repeater can affect hundreds of voice users. Frequencies that serve as voice repeater input frequencies are between 455-460 MHz and 465-470 MHz. The majority of complaints appeared to be occurring with the following community voice repeater input frequencies: 469.500, 469.550, 469.600, 469.625, 469.650, 469.700, 469.725, and 469.750 MHz. All U.S. RTK GPS Licensees are strongly encouraged to avoid use of the repeater input frequencies for data transmission.

Part 90 of the Code of Federal Regulations, 47 CFR 90, contains the complete text of the FCC Rules.