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Extended precision

By Tweaking its global positioning system software package, John Deere doubled the reach of its real-time kinematic (RTK) base stations to 12 miles and potentially lowered the cost of joining the precision steering revolution.

The company also added new capabilities to its non-RTK guidance systems. The change allows systems using SF1 and SF2 signals to continue functioning when obstacles such as trees interfere with GPS satellite signal reception.

Deere calls these new features Long Range RTK and Shading Optimization, respectively. Deere included the upgrades in its late-summer GPS software update, which is free to its GPS system customers. The features are included in all new systems.

Although doubling the reach of RTK base stations could lower the cost of stand-alone and network RTK services, this is not a given, says Kayla Reynolds, product marketing manager for John Deere Ag Management Solutions. The case for lower costs is most clear-cut for farmers who operate their own RTK base stations. “For a farmer, the value is that he may be able to reach more fields with one base station, and may not need two,” she says.

Extended range capabilities will lower costs for Deere dealer-based RTK networks as new base stations are added. Dealers are unlikely to remove and relocate existing base stations, so the new cost regime will take time to work its way into the field, Reynolds says.

“Dealers charge for the signal however they want,” she adds. “If their investment is less, they could decide to lower the annual fee in some cases.”

The extended range feature will give Deere and its dealers a competitive advantage over other RTK providers using base stations with what had been the industry standard 6-mile range, Reynolds says. Taking a look at the numbers gives an idea of the theoretical advantage. A base station with a 6-mile range provides coverage to about 113 square miles. A station with a 12-mile range covers an area four times as large — 452 square miles.

“Typically, the dealer that puts up the network first and has the most coverage gets the most business,” Reynolds says.

RTK software

The new RTK software doesn't alter the physics of RTK signal correction: Line of sight between base stations and GPS-steered vehicles still is required. The power level of RTK radios wasn't changed either. RTK signals have always extended well beyond advertised ranges, but accuracy deteriorates at greater distances.

To extend base station range, Deere upgraded software residing in GPS receivers to filter out “outlier” satellite signals that reduce position accuracy. The software also enabled RTK base stations and vehicle receivers to account for signal biases caused by atmospheric differences because of their separate locations.

These changes improved accuracy enough for Deere to extend its 1-in. accuracy claim to 12 miles. At closer distances, accuracy also was improved. Before the revision, 6-mile accuracy was about 1 in. With the new system, it's now about ¾ in. at that distance, Reynolds says.

Another software enhancement, which Deere calls RTK Extend, allows the system to steer at RTK accuracy levels for up to 15 min. if a vehicle loses the RTK correction signal.

Optimized for shading

The Shading Optimization feature for AutoTrac SF1 and SF2 receivers allows systems to continue steering when trees and other obstructions reduce the number of satellite signals or block out the L2 frequency band. In these situations, steering accuracy could be reduced.

In the past, in order for AutoTrac systems to operate, signals from both L1 and L2 bands, as well as GPS location data from five satellites, were required. Now operation will continue with only the L1 band and data from four satellites.

Competitive products have had this capability, which put Deere at a disadvantage in some areas.

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