Free GPS RTK?

FARGO, N.D. -- In what could be an increasingly important technological advance for the region's farmers, a free RTK base station network soon will expand to cover all of northwest Minnesota.

Most farmers already know about RTK (real-time kinematic) -- the sub-inch accurate global positioning system that depends on a set of government-owned satellite signals It's becoming more common for farm tractors for cropping operations and for tiling and field drainage. The systems usually using a permanent, private system of towers every six to eight miles, or farmer-owned base station towers.

Fewer are familiar with CORS -- a continually operating reference station. Some say CORS is a key to expanding this development into areas without a dedicated tower network. Minnesota's CORS is operated by the state Office of Land Management and the Minnesota Department of Transportation, initially put in play for surveying purposes. The satellite signals so far are free on the Internet, but users must pay for a cellular phone and a monthly fee for Internet access.

Minnesota's system was started in 2001 and has been expanding for several years, according to Dave Broten of General Equipment & Supplies Inc. in Fargo, N.D. His company handles the Leica "mojoRTK" system, which accesses the signal. Iowa's system will be operational in February.

Some technology suppliers like Broten are starting to promote systems to take advantage of the CORS system. Newer CORS systems are getting better and are eliminating a "latency," or signal delay, in early work with the systems.

The systems are getting better at streaming data to the field. Cell phones, often beefed up with external antennae and a signal booster, acquire the data from the Internet. Some signals are directly wired or wired through a Bluetooth wireless and software.

Several states have publicly financed CORS systems.

Minnesota's move

Broten notes that the CORS system is different than the more familiar RTK tower networks. The rural tower network has towers placed at six- to eight-mile intervals so that farmers can have coverage across whole farms.

With the free CORS base station, the link is not a tower, but the cell phone, pulling data from four to six stations at time, all within 20 to 30 miles. Subscribers need to get a name and password from the state, which turns it on when logged into an Internet site."Most people think you've got to be within a certain distance of a tower," Broten says. "With the CORS network, you don't have to."

The system isn't available in North Dakota or South Dakota, per se, but it can be used on land within 25 miles of the Minnesota border.

"When you turn on the 'rover' in your tractor, it is as though you have a base station in your field -- equal or better access as when you're eight miles from a tower.

It costs $12,000 to put a rover system package for every tractor on a farm, plus an annual fee.

Leica offers an annual plan for data transfer. The plan is $400 for three months, $600 for six months and up to $800 for a year.

"That averages $67 to $125 a month, depending on the length of the contract," Broten says.

Some producers want the system primarily for planting, and so may not subscribe the full year.

Arriving in the valley

RTK started making its presence known in the Red River Valley several years ago.

Trimble was the first company selling systems. Farmers either purchased their own radio tower antenna, or became a member of a rural tower network.

Notably, Titan Equipment, RDO Equipment and Butler Machinery have created a joint network that has been expanding for several years. That system charges a fee per rover per tractor, plus an annual fee. The system is growing and the largest of its type in the country, but its coverage area still is limited.

The CORS system started in 2001. The base stations funnel position data into a computer, which refines the corrections before streaming data through the internet to the user. This is different than dedicated RTK towers, where the stations send corrections through a radio link.

Minnesota's system started its high-density area around the Minneapolis-St. Paul area, but it has been working its way out into the state the past few years to cover the state completely.

It has ended up being a utility that more people can use beyond the initial surveying intent. One or the original goals was to guide snowplow trucks in blinding blizzards.

Reference stations usually are cooperative, among government entities. Moorhead, Minn., for example, has had an operating base station before it was part of the CORS network. The CORS network requires a GPS high-grade antenna and a continuous internet link to the main server in St. Paul.

Where they are

The Minnesota system is not alone.

Iowa is building a CORS system, which is expected to be up and running by February. State transportation officials were surprised at how much interest in the system was generated by farmers who wanted to use a Trimble system, upgraded with InTime Connection, which works on an external cell phone and Bluetooth, or mojoRTK.

Wisconsin has a CORS system. Illinois doesn't.

Broten says he's asked the North Dakota Department of Transportation about its interest in developing a CORS system, but has been told that isn't planned. County seats are farther apart in the western part of the state, and cell phone coverage is poorer. Those might be factors, Broten speculates.

He demonstrated the CORS the system at Big Iron, but has yet to sell a unit. He had one on a tractor on a Glyndon, Minn., farm, just east of Moorhead, with a farmer who happens to have a John Deere system. Company officials came from Australia to calibrate and test the system.

One difference is that the tractor carries two antennas on the roof instead of the one antenna setup on tower-based systems. One is the main GPS antenna and the other is used as a compass for terrain and direction. The console is placed where the standard radio is in the tractor and the demonstration model was wired directly into the John Deere display.

For information on Minnesota's CORS, go to www.olmweb.dot.state.mn .

us/CORS.GPS/cors.html.