The SMT100, designed and manufactured by TRUEBNER, combines the advantages of the low cost FDR sensor systems with the accuracy of a TDR system. Like a TDR, it measures the travel time of a signal to determine the dielectric constant of the soil. And like a FDR, it converts this dielectric constant into an easy to measure frequency. But unlike an FDR it isn’t based on a capacitor, but utilizes a ring oscillator to transform the signal’s travel time into the measure frequency. The resulting frequency (>100 MHz) is high enough to operate well in clayey soils.