As an alternative to radio transmission of RTK corrections to a receiver, Carlson has developed Listen-Listen, a cloud-based data-over-IP solution.  Listen-Listen requires an internet connection at the base and rover. The internet connection can be from fixed-line broadband, cellular modems in the GNSS base and rover, data collectors, or Hot-Spots.

Fixed or static IP address sims are not required.  In addition, multiple rovers can simultaneously connect to a single base using Listen-Listen.  It is fully hosted and computed on AWS-based processors and data center, which ensures almost 100 percent up-time.

Traditional onboard UHF radios are generally limited to one-watt power output, which gives a one- to two-kilometer range at best. 35-watt radios give you more range but typically under 5 kilometers with additional complication.  Radio is also subject to terrain obstructions such as hills, buildings and dense tree cover.  As long as there is a cellular signal, there is no restriction on communication range, Carlson’s Listen-Listen works at 5, 10, 20, and even 30-kilometer base lines.

Both easy-to-use and -configure with Carlson SurvCE or SurvPC data collection software, Listen-Listen requires inputting just one four-digit port number at the base station and a four-digit port number at the rover. There is no need to match frequencies, listen for interference, or check a number of other parameters required for UHF communication.  Listen-Listen is a subscription-based service. It works with Carlson’s BRx6 GNSS receiver as a base station and with any rover that is compatible with SurvCE or SurvPC and support RTK corrections by direct IP.

Locate your base in a central location, at a safe/secure location, or over that known point that would not normally be in radio range.  I just recently worked on a project that was a 7-mile corridor.  I would locate the base at one end in a protected area over one of the primary control points and have a connection over the entire project.

Because of the ease and flexibility of setup, Listen-Listen could be you primary communication vehicle.  Radio would be the backup.

FCC LICENSING OF GNSS/RTK SURVEY RECEIVERS EQUIPPED WITH 450-470 UHF RADIOS (and using 35w repeaters)

Recently I purchased new Carlson BRx6+ receivers to replace Hemisphere S320 receivers.  The S320 was equipped with 900Mhz, frequency hopping radios that did not require an FCC license.  The BRx6 receivers are equipped with UHF radios which do require an FCC license. It is illegal to operate a UHF radio in the 450-470 Mhz. frequency regardless of the power used.  The fines, if caught, can be significant.

I could find very little information about setting up the radios, about the appropriate frequencies to use, or about FCC licensing in either the equipment manuals or on equipment supplier websites.  We at US Survey Supply are willing to help our customers setup their equipment but it is the responsibility of the customer to obtain the license with approved frequencies.  There are companies that will help (for a fee) with the license application process. Or, you could potential do it yourself using the FCC ULS (Universal Licensing System).  I had been told that the licensing process was difficult but decided that I should at least try and do it myself.

I am a licensed Ham, so consequently I have a FRN number and knew where to start.  I logged on to the FCC License Manager:  https://wireless2.fcc.gov/UlsEntry/licManager/login.jsp

Most of the information you need for the application is obvious. However, the license application is for a wide variety of license types.  I went back to the internet to try and find specific information that was appropriate for radios furnished with UHF GPS/RTK equipment.  There were several questions on the application where the answers were not obvious or easily found within the FCC website.  Here are areas where I had problems:

• Radio Service Code – I could find nothing on the FCC website that referred to GNSS/RTK receivers or that described a similar application in terms that I could understand.  In retrospect it was obvious, but not definitive.  The code is IG, one of the many codes used under the broad category of “Industries/Business” (47 C.F.R, Part 90). It turns out that I identified the code thru the process of elimination but had little confidence that I had the correct code.
• Station Location – Because operating GNSS/RTK receivers for surveying is a mobile operation, I choose the continental US.  We will get back to this one later.
• Frequency Coordination – This is the first I had heard about frequency coordination.  I left it blank. We will get back to this one later
• Control Point – Still not sure what this is.  I put in my home address.
• Frequency Information – I could find very little information on the appropriate frequencies for UHF GNSS/RTK radio operation.  My search included user manuals, manufacture websites, software websites, internet forums, and Google search.
• Station Class – MO is mobile, so I used it even though a base operation is temporarily fixed
• Emission Designator – this was very difficult to find and is an industry code.

I was able to make it through the application with no obvious errors (The FCC application process goes thru a review at the end to identify inappropriate responses in the application) When I got to the fee page ($170) I stopped.  Even though I had passed the review process, it was apparent, that I did not understand some of the questions and responses in the application.

During my research to find answers for the application I had discovered that there were companies that would help you get your license, for an additional fee.  I also discovered, talking to one of these companies, that they use a “Frequency Coordinator” in the process.

One of the questions on the FCC application referred to “frequency coordination”.  Researching information on the FCC website, I did discover that there is a requirement, in some cases, for “frequency coordination”, as part of the application process.  I did find a list of frequency coordinators in the FCC online information and picked the one that was geographically near me, Forest Industries Telecommunications (FIT).  FIT is a non-profit organization and one of their services is to assist companies and individuals to obtain an FCC license.  During my search thru the internet, Forest Industries Telecommunications (FIT), was the only company that had listed a category for GNSS/RTK operation.

I called FIT and started a conversation with Dave Smith.  He was very willing to answer all my questions and, consequently, give me all the information I needed to correctly fill out the FCC application.  The following are a few key issues that we discussed:

• GNSS/RTK receivers using UHF radios are restricted to the 450 Mhz. to 470 Mhz., range of frequencies. (some of the specifications for receivers list a wider range of frequencies than what is allowed in the US)
• There are thousands of frequencies within this range, but most have some limitation or requirement specific to each frequency. These frequencies can be found in Title 47: Part 90 – 90.35.
• Most of the frequencies require “frequency coordination” and this must be documented and included in the application process
• The only frequencies that do not require coordination are called “Itinerant” frequencies, and there are only 8 frequencies that allow for the typical 35 maximum watt repeaters used in land surveying.
• There is a range of Itinerant frequencies that are “low power” frequencies that are appropriate for most built-in receiver radios (typically 1watt or less)
• Frequency coordination is used to prevent interference between fixed base operations on the same frequency, in the same general location. Consequently, frequency coordination is always location specific.
• Some Itinerate frequencies are generally included in any GNSS/RTK receiver radio license and allows the user to use these frequencies for use statewide or nationwide.
• There is language in the regulations that would limit the number of frequencies (90.35 E), but I was told this is rarely enforced.  However, anything over 10 channels often triggers the request by the Commission for justification.
• Each non-itinerate frequency requires coordination.  However, this can either be fixed, handhelds or mobiles (within a 20-25-mile radius or fixed area).  Each coordination incurs additional effort, and additional cost.
• Each location is generally restricted to a 20-mile radius and under some circumstances can be expanded to a 50-mile radius.

At this point in the conversation I became a little confused by these last two points.  Land surveying was not a fixed base operation.  Companies and individuals in the business of Land Surveying or others that use GNSS/RTK receivers routinely operate in a large geographic area.  I know of several companies and individuals that operate in several states and in many large urban regions.  If they need a specific frequency, tied to a fixed location, to operate within a 50-mile radius every time they setup a GNSS/RTK Base, that could be a large number of frequencies.  This appeared to me to be an unreasonable and unrealistic requirement.  It was at this point that I learned the following:

Historically there were a series of non-itinerant “approved frequencies” that could be licensed to surveyors without being location specific (issued for use statewide or nationwide) and did not require frequency coordination. These non-itinerant frequencies would normally require frequency coordination as a fixed base operation but had historically been approved for GNSS/RTK operation.  There are literally thousands of licenses issued to surveyors that have been approved with these frequencies.  Approximately two years ago, the FCC changed their “policy” and would no longer approve new applications that included these non-itinerate frequencies without the required frequency coordination.

This change was made without any formal notice or public input.  The FCC just stopped approving new applications with the historic “understanding” that had been the case for many years.  These thousands of existing licenses that were approved with these allowed frequencies will probably be allowed to operate in accordance with their current license and will probably be “Grandfathered-in” in any subsequent renewal.  For those of us applying for new licenses, we will be required to follow the regulations for GNSS/RTK operation as described in points 9 & 10 above.

This change makes it more difficult for companies and individuals using GNSS/RTK receivers to be licensed with all of the appropriate frequencies that would be needed within their geographic area of operation.  This change would also increase the use of itinerate frequencies when they are outside any of their licensed fixed base frequencies.  The itinerate frequencies are heavily used in urban areas by many different users using voice as-well-as data communications.  Also, there are just a small number (8) of itinerate frequencies that allow wattage up to and including the typical 35-watt repeaters and base radios used by land surveyors.

There are several issues that will impact the land surveying community resulting from this change in FCC policy.

• Surveyors will need to identify primary work zones.  These work zones will be a 25-mile radius with a fixed center.  The number of work zones will be restricted to 1-3 zones.  Justification will be required for increased radius up to 50 miles and additional zones.
• The change should not have been made without public notification and public review
• The policy may increase the use of the itinerate frequencies which may cause congestion on these frequencies in high population urban areas.
• The historic inclusion of certain non-itinerate frequencies in every GNSS/RTK license will increase the likelihood of interference with new fixed based licenses using these same frequencies. (frequency coordination would not identify conflicts because these frequencies were not location specific)
• Those that already have licenses under the old rules will need to ensure that their license does not lapse.  If they keep their license current, they will probably be “grandfathered-in” and will not be required to follow the new rules.

Based on this information I decided to use FIT for the FCC application process.  In consultation with Dave Smith we decided on the following:

• The inclusion of non-itinerate frequencies with a fixed base location would be useful but, in my case, not necessary. This eliminates the need for frequency coordination.
• I do not plan to use an external radio or repeater but will maintain the added flexibility to use one.  Consequently, the application will include the full list of the 8 high power itinerate frequencies.
• Along with the 8 high power itinerate frequencies, we will include 8 low power itinerate frequencies.
• The location for the use of these frequencies will be the continental US.
• The downside of only using itinerate frequencies is the possibility of traffic on any one frequency.  Having 16 frequencies will increase the chance that a channel will be open.    Also, using low power frequencies where possible will minimize the probability of conflict because of the limited range of low watt radios.