Farmers who rely on GPS for yield monitors or auto-steer on tractors should be aware of some changes that may affect them this fall.

"The Federal Aviation Administration, which manages the Wide Area Augmentation Service or WAAS for GPS differential correction, replaced two older satellites with new ones in July," says Pat Reeg, field operations manager with the Iowa Soybean Association. "The new satellites will provide more accuracy and better signal strength to farmers who use GPS. But in order to receive signal correction from the new satellites, some farmers will have to update the firmware in their receivers."

Some users may have to update firmware

"The change in satellites affects only WAAS GPS," says Reeg. "And not all WAAS receiver systems will be affected. It does not impact OmniSTAR, John Deere SF2 or SF2, or the Nationwide Differential GPS, which is the old Coast Guard Beacon System."

Reeg says if you're not certain whether the change will affect your GPS receiver, all you need to do is turn it on and check to make sure you're receiving a differential correction signal. If you are getting the signal, you're set to go. If not, you'll need to replace the firmware in your receiver with an updated version. Here are some links to common GPS units used today:

www.agleader.com/docs/Support%20Note_WAAS_July07.pdf  
www.ravenprecision.com/WAAS.pdf  
trl.trimble.com/docushare/dsweb/Get/Document-380970/Ag_WAASupdate_SKR_update7-26.pdf  

"Most of the precision ag equipment manufacturers have updated firmware that can be downloaded from their product support site, or you can ask your dealer about it," says Reeg. "Generally, the firmware updates are provided at no cost, but dealers may charge for their time in updating systems for growers."

Without the updated firmware, results from uncorrected GPS will be less reliable because of the uncorrected signal. "Field passes on your yield maps may look more like spaghetti than straight lines," he says.

"This is especially important for growers participating in ISA On-Farm Network replicated strip trial studies, since we're looking for accurate information on which to base future crop production decisions," he adds.

For more information, contact your precision ag dealer or call Pat Reeg at 800-303-1423 or 515-669-9184. The On-Farm Network, a program of the Iowa Soybean Association, assists growers in conducting on-farm studies of crop production products and practices.