Because Miles Opti-Crop division is largely responsible for introducing precision agriculture to western Kentucky, you can trust us to endorse only those products we’ve tested thoroughly in the field. Our client base includes some of the most innovative producers in the world. As a result, we are expected to keep abreast of the latest trends in technology and provide support and guidance when necessary. Opti-Crop demonstrated this level of commitment when it purchased some of the first commercially available yield monitors and recommended them to our clients. In like manner, we purchased some of the first 900MHz GPS receivers and even developed the first privately owned network of differential correction towers in the US to provide the best accuracy to our users. We hope you will find the following information useful.

Choosing The Right GPS Receiver For Your Operation

Differential Correction

Prior to May 1st, 2000, the U.S. Government introduced an intentional error into the signals being outputted by the GPS satellite constellation. This random error, known as Selective Availability (SA) meant a GPS receiver could be off its desired mark by as much as 200 feet. With SA having been removed in May of 2000, the error budget was reduced to about 30 feet. One might question what is the source of the remaining 30 feet error. In a nutshell, the answer is some variables that are out of our control, e.g. the earth’s changing upper atmosphere, satellite drift and the multi-pathing or "bouncing" of signals off tall objects. The good news is there are some companies and government agencies that specialize in correcting these errors and transmit that "differential correction" through another series of satellites or a ground-based network of radio-beacons.

There are a number of providers who offer the above mentioned differential correction service, but that does not mean every GPS receiver can accept every type of correction signal being offered. Special software has to be programmed into a receiver before it is ready to accept any type of correction signal in a useable manner. Some of the radio-beacon based networks offer their signal free to the public, e.g. the United States Coast Guard. Other providers, particularly the satellite based ones, are offered for a fee, e.g. Omni-Star. Your location and geography play an important role in deciding what service to use because not all services have seamless coverage across the United States. For instance, the United States Coast Guard has its network centered along the eastern and western seaboards and major inland waterways. Therefore, someone from Arizona looking for a correction service provider would not consider the Coast Guard signal. This explains why most manufacturers of GPS receivers offer several models with various capabilities to choose from. As a rule of thumb, the more options, the higher the price. When purchasing a receiver, make sure it is capable of using the correction sources that are available in the area(s) it will be used.

Compatibility And Functionality

System compatibility with the equipment it will be connected is an important consideration. Here are some questions one should ask:

1. Does the receiver have enough I/O ports to accommodate your equipment?

2. Are the I/O ports independently configurable? Some applications may require a baud rate of 4800, while others may call for 9600.

3. Does the voltage requirements of the receiver match the power source? A quality receiver should be able to operate over a range of voltages.

4. Are optional cables readily available if a non-standard connection is needed?

5. If data logging is required, does the unit have the capability of storing data in an internal or external memory medium, i.e. internal memory or a PCMCIA card slot?

6. Does the receiver have some type of graphical interface (lights, LED’s, etc) that will allow the user to monitor its status, i.e. power supply, GPS signal, differential correction signal, etc?

7. Does the manufacturer offer peripheral equipment? For example, some companies offer ruggedized field computers to augment their product line. The benefit of buying from such an entity is product conformity. If component compatibility becomes an issue, the manufacturer can not blame someone else’s equipment for poor performance.

Reliability

Production agriculture is a very demanding environment. One’s receiver will likely be subject to various extremes. It is imperative that it be capable of withstanding temperature fluctuations, voltage spikes, vibration, shock, dirt, moisture, electrical noise, corrosive chemicals and gases, and the normal rigors of outdoor use.

Service & Support

This is one element of the purchase decision that should factor in heavily when deciding where to buy. Regardless of what model and make, the manufacturer should have a dedicated support staff to handle any questions or concerns. Most companies in the GPS market sell their products through some type of dealer network. Typically, these dealers are the buyer’s first point of contact when they need help. Any reputable manufacturer will scrutinize who they allow to become dealers and subsequently choose only those parties who demonstrate technical expertise and a willingness to support their product line. It is worth the extra effort to do your homework and select only a dealer who is knowledgeable and willing to answer all your questions in a prompt manner.

Because of the harsh conditions this type of product must endure, in-the-field failures are not uncommon. Make sure the company has the capability to make repairs with a quick turnaround as well as providing a loaner unit when necessary. In addition, there are some models being offered that are non-repairable. In this case, if the unit is damaged, a new one will have to be purchased for the original retail price. One needs to seriously consider the implications.

Product Development & Innovation

The precision ag market is dynamic and those companies who survive long term will be the ones meeting market demand. Look for a company that offers a complete product line and offers firmware updates to current products either free or at a very affordable price. These updates should be able to be done in the field with a laptop or on an office PC. Very rarely should a unit have to be sent to the manufacturer for a firmware update. Obsolescence is always a factor with high-tech equipment, but one should expect to receive at least 4 or 5 years service from the date of purchase.

Product Demonstration

Unless very familiar with the company, request an in-field demonstration. This is especially important if you are purchasing a hardware application like "parallel swathing" to be used with the GPS receiver. Any company not willing to demo their product should be removed from a buy list. A reputable dealer should demo a product and then allow the potential buyer a few days to try it in their operation.

Physical Dimensions

Most receivers are fairly compact and come in a variety of shapes. Some units are even available that combine the receiver and antenna into one unit. This is particularly useful when "cab clutter" must be minimized.

Price

When purchasing a GPS receiver, one needs to understand the trade off between cost and accuracy. There are fundamental differences in the design of a receiver whose accuracy is measured in inches versus one measured in feet. Generally speaking, a positive relationship exists, i.e. the greater the level of accuracy, the greater the price. For example, someone who likes to hike the great outdoors can purchase a hand held GPS receiver with 30 feet repeatable accuracy for less than $300.00(US). A surveyor, on the other hand may need a unit with centimeter accuracy. One would expect to pay around $15 - $20,000.00 for such a unit.

Summary

Buying a GPS receiver should not be traumatic experience. Consider your present and future applications. Purchase a unit that delivers the accuracy you need from a source who can service what they sell. Shop around, but don’t necessarily buy the cheapest unit available; often one gets what they pay for. Because thousands of receivers have already been sold, chances are good that one of your neighbors or friends is currently a user. Ask him or her about their experience with a particular model.

A GPS receiver is the fundamental building block of any field management system. The choice one makes will impact his/her entire precision agricultural program.

Miles Opti-Crop is proud to be an authorized, full-service dealer for Trimble Navigation, Ltd., Mid-West Technologies, Inc., AgLeader Technologies, Inc., and Cultiva, Inc. precision agriculture product lines.  Below the reader will find a listing of our most popular items.

	AgGPS 106 The AgGPS 106 is a WAAS-only differentially corrected GPS receiver combined into a single, compact, waterproof housing. It is the perfect product for someone who wants a low-cost, non-critical application-type receiver.  It is the ideal choice for those engaging in yield monitoring, field mapping, crop scouting and soil sampling. Learn more...
	AgGPS 132 The 132 was the world’s first 12-channel, sub-meter GPS receiver capable of receiving both Coast Guard Beacon and WAAS - both free or a fee-based differential correction service to calculate sub-meter positions in real-time. Because of its easy to read front panel display and programming features, this unit is ideal for a multitude of agricultural applications, i.e. yield monitoring, soil sampling and mapping. Like all of Trimble’s AgGPS products, the 132 is compatible with upgrade options such as data logging and parallel swathing. Learn more...
	AgGPS EZ-Guide Plus The EZ-Guide Plus lightbar is the first to combine crystal clear guidance LEDs, a sunlight readable graphic LCD screen and integrated GPS…All in a slim profile lightbar, which minimizes visual obstruction for the operator. These features give maximum operator feedback – the LEDs provide easy to follow offline guidance day or night and the LCD graphic screen assists with vehicle orientation and guidance during turns and curves. Learn more...

But don't take our word for it, listen to what some of our satisfied Trimble customers have to say…

Being a custom applicator, doing a precise job and getting over more acres at the end of the day is extremely important to me. The Trimble light bar has done that for us. And it has done it in ways that we never really thought of prior to our first purchase two years ago. Spreading dusty lime has always been a challenge until now. We don't have to wait on the dust to clear before continuing and we can run at night to finish a job. Point rows are a breeze now but were a challenge in the past. We can change drivers at any time by using the pause feature, then return to the precise stop/start point. We can also return next week or even next year and go right to the place where we need to start. We don't have to carry water to fill foam markers and waste valuable time filling tanks and in the winter trying to keep them from freezing.

The accuracy of the swaths not only impresses the growers; it makes us come up within tenths of an acre from a GPS field map. Trimble must build rugged units because of the extremely rough terrain, hidden sinkholes, and ditches we encounter. So far, including our second unit we have had no trouble with the hardware. Only operator error, and that is where Steve Bice with Miles Opti-Crop has been very knowledgeable and helpful on several occasions. 1999 was such a dry year we could not see our floater tracks or the litter on the ground from the chicken litter spreader. Spreading at 20 feet swaths really makes the light bar a must.

Mickey Howard
Howard's Agri Service
Calhoun, KY

Mike Sarver of Sarver Farms, Richland, IN had his first taste of Trimble's Lightbar back in the spring of 2000. He was first drawn to the positive benefits of the Lightbar by the Opti-Crop consultants from Miles Farm Service, Hatfield, IN. He then decided to demo one for corn fertilizer application. It only took the operator (Phil Abshier) a couple of hours to grasp the basic concepts of the Lightbar and he was soon to realize the many benefits of using one. Here is what Phil has to say about the Lightbar:

"I have always heard of the benefits from using a Lightbar but did not fully realize their potential until I actually used one myself. Steve Bice first came out to demo the Lightbar to Mike and myself early spring 2000, before it was fit enough to go out in the field. We then decided to demo it for real by mounting it on our tractor that we used for pulling our fertilizer spreader. I soon realized how accurate the Lightbar was. We came within 0.1 acres compared to GPS maps, which meant we could accurately determine fertilizer quantities for each field, without having to allow for overlaps normally associated by ‘guessing’ swath widths. The ‘return to point’ feature allowed us to return to exactly the same point we finished at, whether it be today, tomorrow or next week.

We used the Lightbar throughout the year for fertilizer spreading, NH3 application and DC bean drilling. We have found it to be accurate in all instances plus we have had no problems with system failures, which indicates a well-built unit considering the abuse we have given it. In the event of problems we have encountered, our local consultants Paul Rose and Richard Baylis have always been at hand to provide technical assistance.

I would not hesitate in recommending Trimbles’ Lightbar to any large farmer or custom applicator.

Phil Abshier
Sarver Farms
Richland, IN

For 18 Good Reasons To Use GPS Over Foam Markers Try: http://www.trimble.com/products/pdf/gpsvsfoam.pdf

CenterLine Mid-Tech's CenterLine is your answer to an affordable, easy-to-use guidance system for spraying or fertilizer/lime application.  Compact in design, it boasts many features, such as:  fully adjustable LED's, straight or curved guidance patterns, interior/exterior mount lightbar , logical menu hierarchy, short learning process and a back-lit, wireless remote control unit that is more user friendly than a ordinary TV remote.  This unit comes with a 5 Hz, WAAS only DGPS receiver.  It will also interface with any DGPS receiver that outputs the NMEA 0183 protocol on a RS232 I/O platform @ 5 Hz update with a baud rate of 4800 to 19200 bps. Learn more...

Swath XL Deluxe Mid-Tech’s Swath XL Deluxe is the result of several generations of lightbar design improvements.  It’s tremendous flexibility and multitude of features sets a new standard in ground-based GPS guidance.  The Swath XL Deluxe is the most intuitive, easy to understand lightbar in its class.  Menu navigation on the “Smartpad” follows a logical flow with no unnecessary keystroke or button pushes.  Two points is all one needs to start a days’ work.  The “smartpad” is backlit for nighttime use and allows contrast changes to accommodate varying light conditions.  Various data may be stored on the 20MB ATA flash card that is included in the package. Learn more...

ATC (Ag Technology Center ) Contours, circles, turns or straight lines…the Cultiva Ag Technology Center (ATC) gives you an accurate visual reference of your path on any terrain.  It goes far beyond conventional lightbar systems that tell you only where you are, not where you need to go.  The ATC allows you to see the path before you drive it.  You not only see where you are, but also where you’ve been. With its color LCD display and easy to use menu selections, the Cultiva ATC is the most user-friendly guidance system in the world.  You steer the vehicle as if you’re following a road…What could be easier? Learn more...

Marker LTi With other guidance systems you draw a highway in your mind…  Let Cultiva do the drawing for you.  The Market LT is an easy-to-use agricultural guidance system that combines state-of-the-art GPS with virtual reality display software and hardware.  The Marker LT is very possibly the most intuitive system currently available.  By using a "virtual moving highway," the operator steers the vehicle as if following the lines on a road.  Installation and setup is measured in minutes instead of hours and most anyone can become functional within an hours' use. Learn more...

Yield Monitors
One of the most daunting challenges facing precision agriculture is trying to keep a balanced perspective in light of ever-changing technological advances. To get some idea of how far you've come, look back to where you began. It wasn't too long ago that most farming practices were based on past experience and intuition. The only real-time, "in-the-cab" data collection was what the operator gathered as he peered through the glass. No one is suggesting that a farmer couldn't be successful if he didn't have the latest gadget or gizmo. Good farmers have always succeeded by their keen awareness of yield variations on a field by field basis and strategies to improve them. What they lacked was the technology to validate their suspicions and the tools to correct them on very a specific basis.

Enter the yield monitor. Although considered a recent development, one of the first monitors was actually developed in Europe a quarter century ago. It consisted of a flow sensing plate mounted at the end of the unload auger on the combine. While crude by current standards, it took the technology 25 years to catch up with the concept. Today's yield monitors are very sophisticated and when used in conjunction with GPS, solve the problem of recording "real-time," geo-referenced data on-the-go.

Although overwhelming, the information received from a monitor can form the basis for many operational decisions, i.e. fertility levels, varietal selections, planting populations, irrigation, tiling recommendations, VRT applications, etc. Because some of these decisions require considerable time, money and planning, one should try to achieve a reasonable level of accuracy from their yield monitor. The old adage, "garbage in, garbage out" proves itself.

Before discussing some ways of improving yield monitor accuracy, one must have reasonable expectations. Despite the common misconception, yield monitors were not designed to replace weigh wagons. They were designed to measure yield variations within a particular field. This they do exceptionally well. Concerning accuracy, a 3-5% bu/ac error is normal depending on how closely the calibration procedures are followed. One who is willing to spend the extra time might be able to achieve errors in the 1-2% range; however, it is questionable whether the additional accuracy is necessary. As long as the error rate is consistent, the variation measured will be consistent. Knowing the variation in specific areas of a field allows the grower to sub-divide each farm into identifiable management zones. This allows one to correct problems on a very specific basis and eliminates wasting resources through the "blanket application" approach. The net result should be either a reduction in crop input cost and/or a reallocation of resources. The latter result may seem of little consequence now, but in the future the federal government will probably regulate how many units of N-P-K that may be applied to agricultural acres. If this happens, growers will be forced to become much more precise regarding where each unit of nutrient should be placed in a given area to provide the greatest agronomic, economic and environmental return. Thus, the use of management zones will be necessary.

Yield monitors equipped with GPS are a wonderful tool in deciding how to divide a field into managed areas. From the information gained during harvest, a map is produced that graphically portrays in color what happened in the field. This provides much of the decision criteria when dividing an area into zones because the yield of a crop is the culmination of all the work and factors that influenced it, i.e. seed variety and population, planting depth and speed, crop scouting, fertilizer recommendations, pesticide application, compaction prevention, etc. As an example, lets say one looks at a yield map and observes that one area is consistently wet and the weed pressure is greater resulting in lower yields; this would be a candidate for a specific management zone with respect to herbicide decisions. Another scenario might be a change in soil types and the decision to increase the seeding rate on the more productive series and possibly back off the rate on the poorer soil if no yield response has been indicated on the yield map. If one decides to take the "divide and conquer" approach it will no doubt make the decision making process more complex, but the time will be well spent. Just remember, control the controllable and minimize the uncontrollable.

Although there are a number of yield monitors available on the market, we recommend products designed by AgLeader Technology, Inc. AgLeader introduced the first commercially available yield monitor in the United States in 1992. From then until the present they have been the industry standard by which others are measured. As a company committed to precision agriculture, AgLeader continues to meet the markets’ demand by introducing products built on flexible platforms allowing new functionality to be added in the future. The products below are a good illustration of how a properly designed system can be continually upgraded to meet changing customer demands.

	Insight Insight from Ag Leader Technology is a complete precision farming system.  The primary component of the Insight system is the 10.4-inch color, touch screen display.  Interfaced with GPS and sensors, the Insight display generates color maps of varieties while planting, product application rates while applying fertilizers or chemicals, and yield and moisture maps while harvesting.  The Insight display provides real-time mapping while simultaneously recording many operating parameters and communicates with sensor and controller modules over CAN-bus interface.  Ag Leader Technology's grain harvest sensors have been redesigned to incorporate CAN-bus technology providing increased flexibility and future expandability.  Application control is performed with a new CAN-bus controller module that interfaces with popular non-CAN-bus rate controllers.  The CAN-bus provides an expansion path for future precision farming capabilities of the Insight system.  A flexible internal data model and scalable logging format provide seamless integration of the Insight display with desktop mapping software.
	PFAdvantage Although similar to its siblings (PF3000/PF3000Pro), PFadvantage boasts a much faster processor and rugged internal hardware.  The demands placed on such equipment continue to require more processor capabilities and the PFAdvantage is up for the challenge.  Just like other AgLeader products, it easily installs on all major brands of equipment manufacturers.
	32MB ATA Flash Memory Card The above flash memory card offers the capability of storing large volumes of information in a very compact medium.  Data may be archived, transferred or erased as needed.  This is necessary when a yield monitor is equipped with a GPS receiver. The amount of GPS data received is too large for the internal memory of any yield monitor to store and manage.  The amount of combine harvesting hours a card can handle depends upon what type of logging interval the user has selected during the “set up” procedure of the monitor.  Below is a table illustrating how the logging interval affects number of hours a card can log before requiring the data to be transferred to PC-based software package.

Helpful Hints for Achieving High Accuracy With AgLeader Yield Monitors

Although not critical, it is advisable to name the fields before harvest begins. Doing so will allow the farmer to systematically lay out data in a logical format. If the operator knows when each field will be harvested, it makes sense to enter the field names in the sequence they will be harvested. This will be difficult to do on the first day of harvest when tensions run high.

Perform a visual check of the yield monitor peripheral components at the start of each day. For example, inspect the area cut-off switch spring and chain to make sure it is not kinked and the monitor responds to raising and lowering of header.

Always cut full widths when possible. An efficient operator will generally cut 90 – 100% of the head width most of the time. Because the monitor assumes a constant width, partial swathing without proper adjustments will result in a miscalculation of yields.

Make sure to raise and lower the head at the appropriate time so the area count mechanism actuates at the correct intervals. Lowering will turn the light off which indicates the monitor is logging data. Raising will turn the light on and suspend logging.

When starting a row, do not lower the head until you are a few feet from the row. If the head is lowered prematurely, the monitor is in the logging mode and thinks it is harvesting 0 bu/ac. This can reduce the average bu/ac dramatically.

When finishing a row, raise the head as quickly as possible for the reason stated above.

To the extent possible, avoid cutting lands as this leaves narrow strips which require adjusting the swath width on the monitor. Fewer adjustments minimize the possibility of operator induced error.

Remember that a proper calibration is essential to obtaining accurate data. Be patient and perform as many weight calibrations as necessary to achieve satisfactory results. Generally speaking, the more calibration loads the better. However, when the monitor requires anything over 10 loads, it is quite possible there is an equipment malfunction.

Calibrations are required for each grain type harvested.

Do not adjust slack in the clean grain elevator from the top adjusters. A special plate has been installed at the bottom of the elevator for this purpose. If not followed, current calibrations will be incorrect and new calibrations will be required for all grain types left to harvest. Save yourself the time and frustration and adjust from the bottom.

If the moisture sensor is erratic or displays unusually high values, remove sensor and clean. Foreign matter build-up is especially pronounced in soybeans.

Always back up memory to the monitor and the card at the end of each day. It wouldn’t hurt to do it more than once a day if possible. Failure to do so may result in loss of harvest data.

Do not leave the memory card in the monitor at the end of the day. If it is accidentally pushed into the slot after the monitor is powered off, it will drain the internal battery and harvest data could be lost or corrupted. Ideally, it is best to remove card from combine so that an external copy of data is available in the event of combine fire, theft, damage, etc.

Never format a PCMCIA card that will be used in an AgLeader YM2000 in Windows 95, 98. If necessary to format on an office PC, always format in DOS. If the cards are being used only in a yield monitor, formatting should always done by the yield monitor. Failure to do so may result in a corrupted file structure on the card that could render it useless and the data lost.

For all of your precision agriculture requirements, please contact:

Steve Bice
Office: (270) 926-1786 ext. 230
Mobile: (270) 929-8356
E-Mail: stebic@milesnmore.com

Useful Links:
Trimble
GPS
Imajeep
GPS-INFO.