Regarding Phase Shift.......Detector coils are comprised of transmit windings and receive windings. The transmit portion sends an electronic signal into the earth. When that signal crosses paths with a metallic object, that metallic object creates it's own electronic signal (opposite polarity) which is "picked up" by the receive portion of the coil. The signal coming back to the receive windings is delayed, in comparison to the signal that was transmitted. This delay is caused by resistance (opposition to current flow) and inductance (opposition to the change of current flow) and is called a phase shift. Any object, including the ground itself, that gets involved with the transmit and receive coils provides its own phase shift. And through demodulation, the X-TERRA identifies these objects based on their phase shift(s).
The signal induced in the receive coil, by the magnetic field of the eddy current, can be thought of as being comprised of two simultaneous components. One component is the same shape as the transmit signal. This is called the reactive signal (“X”). Because it is the same shape as the transmit field, the signal responds immediately to what ever the transmit signal is doing. When this X component is subtracted from the eddy current induced signal in the receive coil, the shape of the remaining signal depends only upon the history of the transmitted field, and not the instantaneous value. This signal is called the resistive or loss component (“R”). In order to determine if a target is ferrous or non-ferrous, metal detectors measure the “X” signal. Ferrous targets produce positive (+X) signals and non-ferrous targets negative (-X) signals. Unfortunately, the signals from mineralized soils also produce large positive (+X) signals. This obviously causes a major problem, as the soil signal interferes with target ferrous/non-ferrous measurements, especially because the strength of signal from the soil is often much larger than the target signals. Basically, the target signal must be more distinctive than the mineralization signal in order to determine accurately its properties,particularly the ferrous/non-ferrous nature of the target. The closer the target is to the detector coil, the stronger the target signal. So in mineralized soils, only targets not buried too deeply may be accurately discriminated. The sensitivity to discriminating targets (how deeply a target may be detected) is controlled by the Sensitivity control. Therefore, in mineralized soils, the sensitivity control must be made less sensitive in order to avoid false discrimination.
I haven't ran numbers on the X-50. But here is a post I made four years ago regarding phase shift on the 705:
The number on the display when you ground balance is actually a numeric representation of the phase angle of the ground. That is why I refer to it as the ground phase number, not the ground balance number. Ground phase does not tell us how strong the mineralization is. But it does tell us if it is more magnetic in one area than another. (smaller ground phase numbers are indicative of more magnetic soil conditions and larger ground phase number are typical of less magnetic soil.) Regardless, when you properly set the ground balance on the 705, you are electronically adjusting what the detector interprets as the phase angle of the ground. The parameters of the ground phase adjustments on the 705 are: 0 = -1 degree .................. 90 = +9 degrees. So in your example, when you are able to ground balance your 705 with a ground phase reading on or around 20, your detector has determined that the ground at that specific location requires a "phase shift"" of approximately +1 degree, to allow your detector to "compensate" for the phase angle of that soil. If you don't properly ground balance your detector, TID numbers become skewed and you can actually end up getting an audio response from the soil itself.
