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In the Shop

RSS By: Dan Anderson, Farm Journal

As a farm machinery mechanic and writer, Dan brings a hands-on approach that only a pro can muster. Along with his In the Shop blog, Dan writes a column by the same name as well as the Shop Series for Farm Journal magazine. Always providing practical information, he is a master at tackling technical topics and making them easy for all of our readers to understand. He and his wife, Becky, live near Bouton, Iowa.

More Ways To Mess Up A GPS Guidance Signal

Oct 19, 2012

 I've mentioned before that FM business band radios under certain circumstances can interfere with the operation of GPS-based guidance systems in farm equipment. I don't understand all the complexities of frequency overlap, electromagnetic interference and other ways that radios, antennas, wiring harnesses and amplifiers can get in each other's way. But they do, and the more electronic gizmos we take to the field, the more opportunities there are for interference.

For example, I've heard of situations where combines lost their GPS guidance signal whenever they passed near a particular semi truck parked on the endrows. Once they were away from the semi, they were able to recalibrate and reaquire the GPS signal. One theory is that the radio signal for the remote controls for the grain trailer's electric tarp and electric hopper open/close doors was overriding the GPS signal to the combine.

In another case I heard about, farmers have installed aftermarket radios in their combines, tractors or other GPS-guided machines and subsequently developed problems with their GPS system, even when the radios were off. The theory about that relationship is that radios maintain a certain level of "on" even though the indicators on the radio show it is off. Apparently, that minimal radio activity was enough to disrupt the machine's GPS signal. Diagnosis came when the aftermarket radio was disconnected from battery power, and the GPS signal returned.

The list of things that have disrupted GPS signals on farm equipment continues to grow: the location of a CB or FM radio antenna in relationship to the GPS receiver on top of the cab; the location of the actual radio inside the cab, in relation to the GPS processor/controller; satellite radio antenna cables that pass too close to GPS components or wiring harnesses; cell phone towers in or near fields; wireless TV cameras mounted on the rear of combines, sprayers or planters; there have even been rumors that the electronic "noise" from the engine circuitry of some late model semi trucks can confuse the GPS system in farm machinery.

The consensus is that if the GPS system on a piece of farm equipment mysteriously loses its signal, one of the first things to consider is whether or not there is a piece of electronic gadgetry in the machine or near the machine that uses or emits radio signals. Since we're using more and more remote control devices to see, control, guide and entertain us while we're in the field, there are more and more opportunities for one or more of those gadgets to electronically get in each other's way.

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