Heilig uses a free WAAS (Wide Area Augmentation System) signal to improve the accuracy so he can reduce skips and overlaps between passes. WAAS is an ubiquitous signal developed by the Federal Aviation Association for the airline industry that provides differential correction typically within 6 to 8 inches of pass-to-pass accuracy.
“We purchased the least-expensive system and put it on our tillage tractor, and it works more than adequately for what we wanted in terms of field work, chemical application, those kinds of things,” Heilig says.
On the intermediate-sized tractor that he uses for cultivation and planting, Heilig installed another EZ-Guide 500 with an upgraded OmniSTAR XP guidance signal that provides the operator with 3-inch accuracy. The OmniSTAR system costs about $3,000 more, plus an additional $800 annual subscription to get access to the international OmniSTAR satellite network.
Heilig used that system this year to plant beans and also says he will use it to shape beds and plant and cultivate potatoes next spring.
“That unit worked remarkably well,” he says. “I was extremely pleased with it. I’ve got one circle that has a corner on a hillside and it literally laid those rows in there perfectly.
“Before we had to do it by hand, which—depending on the capability of your applicator or tractor operator—would determine how accurate your planting would be. The GPS system certainly exceeded what we could do, and our guess row accuracy before was actually very, very good.”
The system Heilig purchased is about $10,000 to $15,000 less than the most expensive one.
High-end versus low-end systems
The difference between the more expensive GPS systems and the entry-level ones is the accuracy of the type of signal they receive, says Steve Gilbert, manager of GPS dealer Ag Tech Services in Moses Lake.
Satellite signals used in GPS must be corrected as they come through the atmosphere. Ubiquitous signals, such as WAAS, are free but only provide accuracy within 6 to 12 inches.
The most expensive RTK (real-time kinematic) signal can let a grower turn on a dime but requires a significant investment. Growers must install a $13,000 base station near their fields or subscribe for $1,000 annually to a signal triangulation service provider.