Near Intersection of I-35 & I-90 Southern Mn. | The original Raven 400 expected to use a magnetic wheel sensor or some device that produced a rather low output rate. Generally this meant using a Raven magnetic speed sensor with two pairs of magnets. The magnets were spaced equally about a non-driven wheel and in an alternating pattern of North and South Poles. The speed calibration number was the working circumference of the wheel for 10 revolutions. I commonly used a speed cal of 1100 with a rather large front tractor tire.
Another choice that was quite popular during that time was a Micro Trak product called a Trak-Star. This was not a true radar gun but used ultra sound to reflect back off the ground. With the proper cable the Trak Star would output a signal compatible with the SCS-400. There were reliability issues with the Trak Star.
About that time radar became available for the Ag Market mostly for use with planter monitors. The radar gun puts out a much faster output. That meant if it were connected to the SCS-400 a very small speed calibration number was needed. Typically this was between 6 and 7. Since the 400 did not allow the use of a decimal point, it was not possible to enter in 6.1 etc to achieve the proper calibration.
One solution was an external "divide by" circuit between the radar gun and the SCS-400. Raven's version used two "divide by 10" circuits cascaded together to achieve a "divide by 100" result. This is somewhat akin to a slowdown gearbox where 100 RPM in results in 1 RPM out. This allowed the use of a number such as 612 for the calibration. This was a small metal box often attached to the back of the SCS-400
GPS emulated radar is the same situation. In other words using either a true radar gun or a GPS emulating radar will have the same problem of having to use a very small speed calibration number which prevents accurate calibration.
I used the magnetic speed sensors for many years with good success. The major problem was debris cutting the cable. Often the cable could be cut at the damaged point and a pair of connectors placed at that spot. If the damage was close to the sensor there would not be enough room to attach a connector.
You ask: Can I even get either of these formatted to put out something that the old raven likes? I don't know if the interface boxes that reduced the speed are available anymore. Someone may have one lying around.
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GPS speed for raven 400
