You may have been wondering what the ferrite core on the APAS T1 soil moisture sensor cable is for?
The short answer is that "it's for EMI (Electromagnetic Interference) noise reduction"!
Noisy soil moisture readings due to cable interference or a bad power supply may appear mysterious and cause a lot of headaches.
Good soil moisture sensors usually operate at a high frequency (MHz - GHz), and have a high sphere of influence (detect moisture in a larger volume of soil), which is at its peak when moisture levels are high.
Such a soil moisture sensor can be assumed an antenna that is installed in the soil rather than in the air. The sensor cable can act as the extension of this antenna, interfere with the sphere of influence, and therefore cause fluctuations in sensor readings (noise).
To reduce EMI for FCC regulatory compliance, and to minimize any noise caused by the aforementioned sources, we have added a high quality ferrite bead to the circuitry and a snap-on ferrite core to the sensor cable (research-grade sensor variety only).
Depending on the application and noise level, the current ferrite core can be removed, replaced by a larger one, or another one can be added to the other end of the cable.
You can more information on this in the APAS T1 sensor user manual.
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